BASIC
HYDRAULICS
LEARNING
ACTIVITY
PACKET
HYDRAULIC SPEED CONTROL
TM
BB831-XA04XEN
LEARNING ACTIVITY PACKET 4
HYDRAULIC SPEED CONTROL
INTRODUCTION
LAP 2 covered the speed control of actuators using a needle valve or by feathering
the DCV. This LAP will explain the details of why a needle valve or feathering a DCV
causes the flow rate to be reduced.
Also, this LAP will discuss two new valves: the flow control valve and the check
valve. These valves will then be used to design a number of circuits that control actuator
speed.
ITEMS NEEDED
Amatrol Supplied
1 85-BH Basic Hydraulic Training System
1 85-HPS Hydraulic Power Unit
School Supplied
1 Stopwatch
1 Allen Wrench Set
FIRST EDITION, LAP 4, REV. B
Amatrol, AMNET, CIMSOFT, MCL, MINI-CIM, IST, ITC, VEST, and Technovate are trademarks or registered
trademarks of Amatrol, Inc. All other brand and product names are trademarks or registered trademarks of their
respective companies.
Copyright © 2014, 2009 by AMATROL, INC.
All rights Reserved. No part of this publication may be reproduced, translated, or transmitted in any form or by any
means, electronic, optical, mechanical, or magnetic, including but not limited to photographing, photocopying,
recording or any information storage and retrieval system, without written permission of the copyright owner.
Amatrol,Inc., 2400 Centennial Blvd., Jeffersonville, IN 47130 USA, Ph 812-288-8285, FAX 812-283-1584
www.amatrol.com
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TABLE OF CONTENTS
SEGMENT
1 RELIEF VALVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
OBJECTIVE
OBJECTIVE
OBJECTIVE
SKILL
OBJECTIVE
1
2
3
1
4
SEGMENT
2 CHECK VALVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Describe the function of a relief valve and give an application
Describe the operation of a direct-acting relief valve and give its schematic symbol
Describe how a relief valve is used for system protection
Connect a relief valve in a circuit to limit pressure in the system
Describe how a relief valve is used for speed control assistance
Activity 1 Relief valve operation with speed control
OBJECTIVE 5 Describe the function of a check valve and give an application
OBJECTIVE 6 Describe the operation of three types of check valves and give their schematic symbol
Activity 2 Check valve operation
SKILL 2 Design a circuit to provide bypass flow
SEGMENT
3 FLOW CONTROL VALVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
OBJECTIVE
OBJECTIVE
SKILL
OBJECTIVE
7
8
3
9
SEGMENT
4 METER-IN AND METER-OUT CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
OBJECTIVE 10
SKILL 4
OBJECTIVE 11
SKILL 5
SEGMENT
Describe the operation of a meter-in flow control circuit and give an application
Connect and operate a meter-in flow control circuit
Describe the operation of a meter-out flow control circuit and give an application
Connect and operate a meter-out flow control circuit
5 FLOW CONTROL CIRCUIT DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
OBJECTIVE 12
SKILL 6
OBJECTIVE 13
SKILL 7
SEGMENT
Describe the function of the flow control valve and give an application
Describe the operation of a flow control valve and give its schematic symbol
Connect and adjust a flow control valve to control speed of an actuator
Describe the effect of actuator load changes on flow control valve operation
Activity 3 Effect of actuator load changes on flow control valve operation
Define independent speed control and give an application
Design an independent speed control circuit
Explain how speed control valves can be used to provide multiple speeds
Design a two-speed actuator circuit
6 FLOW RATE VS. CYLINDER SPEED. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
OBJECTIVE 14
SKILL 8
OBJECTIVE 15
SKILL 9
OBJECTIVE 16
SKILL 10
Describe how to calculate the extend speed of a hydraulic cylinder
Calculate the extend speed of a hydraulic cylinder given its size and a flow rate
Describe how to calculate the retract speed of a cylinder
Calculate the retract speed of a cylinder given its size and a flow rate
Describe how to calculate the stroke time of a cylinder
Calculate the cylinder stroke time given its size and a flow rate
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SEGMENT 1
RELIEF VALVES
OBJECTIVE 1
DESCRIBE THE FUNCTION OF A RELIEF VALVE
AND GIVE AN APPLICATION
Relief valves are used in hydraulic systems to allow pump flow to
bypass the system and flow directly to the reservoir. Two applications
are:
• Protecting system components from high pressure.
• Assisting flow control valves in controlling actuator speed.
A typical relief valve is shown in figure 1.
Figure 1. Typical Relief Valve Used in Industrial Hydraulics
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OBJECTIVE 2
DESCRIBE THE OPERATION OF A DIRECT-ACTING
RELIEF VALVE AND GIVE ITS SCHEMATIC SYMBOL
There are two relief valve designs commonly used in hydraulic
applications. One type is the direct-acting design. The other type is a
pilot-operated or two-stage relief valve to be described in a later LAP.
The basic function of each valve type is the same: each opens at a preset
pressure to allow flow to return to the reservoir. However, the
construction of each is different.
Three types of direct-acting relief valves are shown in figure 2. Each
consists of a body with two ports: an inlet and an outlet. Inside the body
is a movable member that is held in the closed position by a spring.
T
T
T
P
P
P
POPPET TYPE
SPOOL TYPE
BALL TYPE
Figure 2. Direct-Acting Relief Valve Types
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Using the poppet type, also called the dart type, figure 3 shows the
operation of the direct-acting relief valve when the pressure at the inlet
port reaches a certain level. The pressure creates enough force to push
the poppet off the seat and allow oil to flow through to the outlet. By
adjusting the compression on the spring with an adjuster, the pressure
level where the valve opens can be changed.
VALVE CLOSED
INLET
BODY
POPPET
OUTLET
VALVE OPEN
SPRING
PRESSURE
ADJUSTER
TO RESERVOIR
Figure 3. Basic Operation of a Direct-Acting Relief Valve
The schematic symbol is the same for the direct-acting and
pilot-operated relief valves and is shown in figure 4. Notice that the
explanation of the symbol in figure 4 shows what each part of the
symbol means. This valve is a normally closed valve. You can tell this
from the symbol because the arrow in the block is shown not connecting
the inlet and outlet.
The dashed line is an internal line called a pilot line which causes the
valve to open (raises the arrow). The spring indicates that the valve
opens at a certain pressure. The angled arrow through the spring tells you
that the pressure is adjustable.
Finally, notice that the pilot line connects to the valve’s inlet. This
tells you that the valve senses inlet or upstream pressure only.
SYMBOL
EXPLANATION
ADJUSTABLE
INLET
OUTLET
NORMALLY
CLOSED
PILOT
TO OPEN
Figure 4. Relief Valve Schematic Symbol
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OBJECTIVE 3
DESCRIBE HOW A RELIEF VALVE IS USED
FOR SYSTEM PROTECTION
Almost all hydraulic systems have a relief valve in the circuit to act
as a safety device in case the pressure becomes too high. High pressure
can occur in a hydraulic system if the pump’s flow is blocked for some
reason.
The relief valve’s primary purpose is to limit system pressure during
normal operation as well as when a component malfunctions. During the
normal operation of a hydraulic system, the flow to the circuit will be
blocked for periods of time. This includes when the directional control
valve is in a blocked center condition, when a cylinder becomes
extended or retracted, or when an actuator is stalled by an excessive load.
SKILL 1
CONNECT A RELIEF VALVE IN A CIRCUIT TO LIMIT
PRESSURE IN THE SYSTEM
Procedure Overview
In this procedure, you will connect a pilot-operated
relief valve to act as a safety device to limit the pressure in
the system whenever the pump’s flow is blocked by the
circuit. This skill will also show that the relief valve
performs this function several times during a normal cycle.
❑ 1. Set up the cylinder reciprocation circuit shown in figures 5 and 6.
In this circuit, you will cycle the cylinder using a directional
control valve. During each part of the cycle, you will observe the
flow from the relief valve’s outlet to determine whether it is open
or closed.
Although all relief valves must be drained, most are internally
drained. The relief valve is understood to be internally drained
when no external drain line is drawn. Notice that this relief is
externally drained and must have the drain connected to the return
manifold. This is because this valve is also used in the Amatrol
trainer to perform the function of a sequence valve in a later LAP.
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Notice that this relief valve has its ports numbered. Port 1 is the
inlet, port 2 is the outlet and port 3 is the drain.
HYDRAULIC INSTRUMENTATION PANEL
GAUGE A
GAUGE B
FLOW
METER
GAUGE C
DRAIN
LINE
SUPPLY
MANIFOLD
RELIEF \ SEQUENCE
VALVE
CYLINDER
PRESSURE REDUCING
VALVE
1
1
2
FLOW
FLOW
CONTROL CONTROL
#1
#2
A
A
2
3
3
NEEDLE
VALVE
B
A
B
MOTOR
B
RETURN
MANIFOLD
IN
D.C.V.
#1
CHECK VALVE #1
A
CYLINDER
HYDRAULIC ACTUATOR MODULE
B
OUT
B
A
CHECK VALVE #2
B
A
BASIC HYDRAULIC VALVE MODULE
Figure 5. Pictorial of the Circuit for Observing Relief Valve Flow
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NOTE
A drain line is shown in a schematic diagram as a dotted line,
as shown in figure 6.
GAUGE
A
SUPPLY
MANIFOLD
RELIEF
VALVE A
1
IN
IN
A
OUT
B
DRAIN
3
SMALL
BORE
CYLINDER
2 OUT
RETURN
MANIFOLD
Figure 6. Schematic of Circuit for Observing Relief Valve Flow
❑ 2. Perform the power unit checkout procedures.
❑ 3. Close the shutoff valve.
❑ 4. Turn on the power unit and set the power unit’s relief valve to 500
psi/3450 kPa.
A fixed displacement pump will continue to push oil into the lines
causing the pressure to rise until a line bursts or the electric motor
stalls. The relief valve avoids this problem by opening at some safe
pressure level and allowing the flow of oil to dump back to the
reservoir.
❑ 5. Open the shutoff valve and set the pressure of relief valve A (the
one shown in figures 5 and 6) at 400 psi/2760 kPa.
This is done by turning the adjustment knob of relief valve A until
the pressure at Gauge A shows 400 psi/2760 kPa.
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❑ 6. Test the operation of the relief valve by extending and retracting
the cylinder. As you do this, notice when relief valve A is closed,
the flowmeter reads zero flow and when relief valve A is open, the
flowmeter reads full pump flow. Observe the pressure and relief
valve status (opened or closed) for each condition.
NOTE
When the cylinder is fully extended or retracted, hold the
DCV’s lever actuated while you make the flow and pressure
readings.
CIRCUIT
CONDITION
GAUGE A
(psi/kPa)
RELIEF VALVE STATUS
(open/closed)
Cylinder extending
Cylinder extended
Cylinder retracting
Cylinder retracted
DCV centered
You should have observed that the relief valve opens when the
flow to the system is deadheaded or blocked. This occurs when the
cylinder is extended, retracted, or the DCV is centered.
Figure 7 shows what happens when the flow has been deadheaded
or blocked. The oil from the pump continues to flow into the
supply line even though it is blocked. As the pump continues to
push oil into the supply line, the oil pressure rises rapidly to 400
psi / 2760 kPa. Because 400 psi / 2760 kPa is the pressure setting
of relief valve A, it opens when the pressure at the inlet reaches a
pressure of 400 psi/2760 kPa and allows the flow to dump to the
reservoir, stopping the rise in pressure.
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NOTE
It is important to understand that when the relief valve is said
to be open, this means that the relief valve has opened far
enough to allow the full pump flow to go through it. This does not
mean that the valve is opened as far as it can go.
Instead, the valve increases its opening until the full flow of
the pump can go through it. The pressure at which this occurs is
controlled by the relief valve’s spring.
DCV
SHIFTED
GAUGE A
400psi / 2070kPa
RELIEF
VALVE A
IN
A
OUT
B
OIL FLOW IS
STOPPED
CYLINDER
FULLY
RETRACTED
M
SYSTEM RELIEF VALVE SET
AT 500psi / 3450kPa
(DOES NOT OPEN)
Figure 7. Relief Valve A Operating as a Pressure Limiting Device
❑ 7. Adjust relief valve A to another setting such as 300 psi/2070 kPa.
❑ 8. Then repeat step 6 to see if the relief valve’s pressure setting has
any effect on when the relief valve is open and closed.
You should observe no difference in the operation of the relief
valve.
❑ 9. Reduce the power unit relief valve to the minimum setting, close
the shutoff valve and turn off the power unit.
❑ 10. Move the handle of the DCV back and forth to remove any
pressure in the circuit.
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OBJECTIVE 4
DESCRIBE HOW A RELIEF VALVE IS USED
FOR SPEED CONTROL ASSISTANCE
Another application for the relief valve is to work with the needle
valve in controlling the speed of an actuator. This is accomplished by
restricting pump flow with the needle valve, increasing pressure to a
level that causes the relief valve to partially open and dump a part of the
pump’s flow. The remaining pump flow goes to the actuator. As a result,
the actuator moves at a slower speed.
EXTENDING
970
PSI
NEEDLE
VALVE
560
PSI
LOAD
P
A
R
B
3 GPM
540
PSI
40
PSI
990
PSI
DCV
SHIFTED
2 GPM
M
SET FOR
1000 PSI
5 GPM
Figure 8. Relief Valve Operating with a Needle Valve for Speed Control
This range of pressure between fully closed and fully opened is
usually very small (i.e. 50 psi). When you set the relief valve pressure,
you are actually setting the full open pressure. This is when all flow is
going through the valve. But, the relief valve actually starts to open at a
slightly lower pressure. This is called the cracking pressure.
If the pressure downstream in the circuit increases to a point between
the cracking pressure and downstream pressure, some part of the pump
flow will be directed over the relief valve. For example, in figure 8, the
full open pressure of the relief valve is 1000 psi. However, the cracking
pressure is 980 psi.
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Without the needle valve, the pressure would be about 560 psi while
the cylinder is extending due to the load and the DCV. This means that
full pump flow would be going to the cylinder if the needle valve were
not in the circuit. By putting the needle valve in the circuit, we can create
another pressure drop to make the system pressure rise to 990 psi which
is enough to cause the relief valve to partially open and divert some of
the flow across the relief valve.
Activity 1. Relief Valve Operation With Speed Control
Procedure Overview
In this procedure, you will demonstrate how the needle
valve and relief valve combine to control the flow rate in a
circuit. To do this, you will measure the pressure when the
relief valve first starts to open and then observe the flow as
pressure increases to the relief valve’s pressure setting.
❑ 1. Connect the circuit shown in figure 9.
In this circuit, the needle valve will control the flow to the motor.
The externally drained relief valve will be used to show that the
excess flow not used by the circuit is diverted over the relief valve.
NOTE
The hose with the open-end fitting is shown in figure 10. The
open-end fitting being held over the opened filler/breather is
illustrated in figure 11.
NOTE
Verify that the flywheel is removed from the motor shaft. If it is
not, use a 3/32-inch allen wrench to remove it as you did in LAP
2 (Skill 4).
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GAUGE
A
SUPPLY
MANIFOLD
B
A
NEEDLE
VALVE
SHUTOFF
VALVE
1
2
RETURN
MANIFOLD
MOTOR
3
RELIEF
VALVE A
OPEN END
FITTING
FILLER
BREATHER
PORT
Figure 9. Schematic of Circuit for Demonstrating the Operation of the
Needle Valve/Relief Valve Combination
Figure 10. Hose End with Open-End Quick-Connect Fitting
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Figure 11. Using the Open-End Fitting to View Flow Returning to
Reservoir Through the Filler/Breather Opening
❑ 2. Perform the power unit checkout procedures.
❑ 3. Close the needle valve completely.
❑ 4. Turn on the power unit and adjust the power unit relief valve to
500 psi/3447 kPa.
CAUTION
Before going to step 5, be sure the filler/breather cap has
been removed and the hose with the open-end fitting is directed
into the open reservoir.
❑ 5. Open the shutoff valve.
❑ 6. Adjust the setting of relief valve A until Gauge A reads 350
psi/2415 kPa. This is the full flow setting of the relief valve.
❑ 7. Open the needle valve completely by turning its adjustment knob
fully CCW.
You should observe that the pressure at gauge A drops low enough
to cause the relief valve to close and direct the pump’s full flow to
the motor.
The motor is now running at full speed.
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❑ 8. As the motor is running, slowly turn the needle valve knob CW.
As you do this, observe the flow from the outlet of relief valve A.
Record the pressure at Gauge A where the relief valve first starts to
open. This is the cracking pressure.
Cracking Pressure _______________________________(psi/kPa)
The cracking pressure should be approximately 330 psi / 2277 kPa.
❑ 9. Continue to slowly turn the needle valve’s knob CW. Observe the
flow through the relief valve and the speed of the motor.
You should observe that the motor slows down as the amount of
flow through the relief valve increases.
When the pressure stops increasing at Gauge A, you have reached
the relief valve’s pressure setting. This is where full flow is going
through the relief valve. The motor should then stop.
Relief Valve Pressure Setting_______________________(psi/kPa)
This should be the same pressure you set in step 6 (350 psi/2415
kPa).
❑ 10. Now change the pressure setting of relief valve A to 400 psi/2760
kPa.
❑ 11. Repeat steps 7-9 to see if the difference between system pressure
and cracking pressure changes when the relief valve setting is
different.
Cracking Pressure _______________________________(psi/kPa)
The cracking pressure should be approximately 380 psi / 2622 kPa.
Relief Valve Pressure Setting_______________________(psi/kPa)
This should be the pressure you set in step 10 (400 psi / 2760 kPa).
You should find that the difference does not change.
❑ 12. Reduce the power unit relief valve to minimum, turn off the power
unit and close the shut-off valve.
❑ 13. Remove the open-end quick-connect fitting and replace the cap on
the filler-breather.
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SEGMENT 1
SELF REVIEW
1. The primary purpose of a relief valve is to _________
system pressure.
2. When using a needle valve to control speed, excess pump
flow is directed over the _______ valve.
3. When operating in a flow control circuit, the speed of the
actuator ___________ when the flow through the relief
valve increases.
4. The two types of relief valves are ______________ and
pilot-operated.
5. Turning the adjustment knob on a relief valve changes the
compression on the __________.
6. The __________ pressure is the point where the relief valve
starts to open.
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SEGMENT 2
CHECK VALVES
OBJECTIVE 5
DESCRIBE THE FUNCTION OF A CHECK VALVE
AND GIVE AN APPLICATION
The check valve is a valve that allows fluid to flow in one direction
and completely blocks flow in the other direction. It is considered to be a
one-way directional control valve. Figure 12 shows a check valve used
with the Amatrol 850 Series trainer.
Figure 12. Check Valve Used in the 850 System
The check valve is one of the most commonly used hydraulic valves.
The circuit shown in figure 13 shows four common applications:
• Holding Prime - It is common for the oil to drain out of the inlet line
of a hydraulic pump when it has not been run for a long period. This
is called “losing the prime of the pump.”
Most larger pumps have difficulty regaining prime because the
atmospheric pressure is not enough to push the oil up the supply tube
to the pump’s inlet. A check valve is often installed in the inlet line
to hold the oil in the line.
• Avoid Pump Reversal - There are some types of hydraulic circuits
where the oil in the circuit will be forced through the pump
backwards if the electric motor is turned off. Many pumps can be
damaged if they are driven backwards. To avoid this problem, a
check valve is often installed at the outlet of the pump to keep the oil
pressure in the circuit from driving the pump in the reverse direction.
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3. BYPASSES
NEEDLE
VALVE IN
ONE FLOW
DIRECTION
2. AVOIDS
REVERSAL
OF PUMP
1. HOLDS
PUMP
PRIME
4. GENERATES
BACK- PRESSURE
IN THE SYSTEM
Figure 13. Four Common Check Valve Applications
• Bypass - Check valves are often used in circuits to bypass the flow
around certain components in one direction. This allows the
component to control the circuit’s operation in one direction and
have no effect in the other direction.
• Back Pressure - Many larger directional control valve designs use oil
pressure to shift the spool. With some designs there is a minimum
system pressure that must exist in order to shift the spool. A check
valve is often placed in the tank port to create a back pressure
sufficient to shift the spool.
Check valves are also used in other applications for holding
actuators locked in position and providing a free flow of oil to a
hydraulic motor as it decelerates to a stop. These applications will be
explored in later LAPs.
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OBJECTIVE 6
DESCRIBE THE OPERATION OF THREE TYPES
OF CHECK VALVES AND GIVE THEIR SCHEMATIC SYMBOL
There are three common types of check valves used in hydraulics:
• Ball
• Poppet
• Swing
Cross-section sketches of each type are shown in figure 14. These
three valves all perform the same function: oil flows freely in one
direction and is blocked in the other direction.
BALL CHECK VALVE
BODY
BALL
POPPET CHECK VALVE
SPRING
FLOW
POPPET
BLOCKED
FLOW
BLOCKED
SWING CHECK VALVE
FLAPPER
FLOW
BLOCKED
Figure 14. Types of Check Valves
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The check valve schematic symbol, shown in figure 15, is the same
for all three types.
SYMBOL
EXPLANATION
FREE FLOW
CHECK VALVE
INDICATES
BLOCKED
FLOW
RIGHT
TO LEFT
DENOTES
FREE FLOW
LEFT TO
RIGHT
OR
FREE FLOW
DENOTES
A SPRING
REQUIRED
Figure 15. Check Valve Symbol with Explanation
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Activity 2. Check Valve Operation
Procedure Overview
In this procedure, you will demonstrate that a check
valve stops flow in one direction and allows it to flow freely
in the other direction.
❑ 1. Set up the circuit shown in figure 16.
In this circuit, the check valve will open in one direction to allow
oil to flow through the DCV. In the other direction, it will stop
flow.
To hook up the check valve correctly, connect it as shown in the
schematic in figure 16.
IN
A
B
OUT
B
A
IN
OUT
Figure 16. Check Valve Test Circuit
❑ 2. Perform the power unit checkout procedures.
❑ 3. Turn on the power unit and increase the relief valve’s pressure
setting to 300 psi/2070 kPa.
❑ 4. Open the shutoff valve.
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❑ 5. Push in the lever of the DCV and observe the flow meter reading.
Flow Rate ___________________________________(gpm / lpm)
You should observe that the check valve is now full open, as
shown in figure 17. You can tell this because the flow meter is
reading the pump flow (approximately 2.6 gpm / 9.8 lpm).
This check valve uses a poppet and spring to control the flow of
fluid through the valve. The spring is only strong enough to allow
the poppet to block the passageway. A very low pressure can push
it open.
FREE FLOW DIRECTION
VALVE
BODY
FREE
FLUID
FLOW
SPRING
POPPET
Figure 17. Free Flow Operation of a Check Valve
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❑ 6. Now pull out on the lever of the DCV and observe the flow meter
reading.
Flow Rate ___________________________________(gpm / lpm)
You should observe that the check valve is blocked in this
direction, as shown in figure 18. You can tell this because the flow
meter reading is zero.
When the fluid tries to flow in the other direction, it pushes the
poppet harder against the seat (figure 18). This completely blocks
off the fluid flow through the check valve. This direction is called
the “checked” or “blocked” direction. In the checked direction,
these valves leak very little, or not at all.
BLOCKED FLOW DIRECTION
VALVE
BODY
FLUID
FLOW
BLOCKED
SPRING
POPPET
Figure 18. Block Flow Operation of a Check Valve
❑ 7. Release the DCV lever.
❑ 8. Repeat steps 5-7 several times to further test the operation of the
check valve.
❑ 9. Reduce the relief valve setting to a minimum, turn off the power
unit and close the shutoff valve.
❑ 10. Move the handle of the DCV back and forth to remove any
pressure in the circuit.
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SKILL 2
DESIGN A CIRCUIT TO PROVIDE BYPASS FLOW
Procedure Overview
In this procedure, you will design a circuit that will use
a check valve in a basic application.
❑ 1. Complete the design of the circuit shown in figure 19 so the
cylinder can be reciprocated with a directional control valve. The
cylinder should extend at a slow speed (adjustable by the needle
valve) and retract at a high speed.
IN
A
OUT
B
Figure 19. Partial Schematic
❑ 2. Connect your circuit design on the 850 Series trainer using the
❑ 3.
❑ 4.
❑ 5.
❑ 6.
small bore cylinder.
Perform the power unit checkout procedures.
Turn on the power unit and increase the relief valve’s pressure
setting to 300 psi/2070 kPa.
Open the shutoff valve.
Close the needle valve completely. Then open it 1/2 turn.
This will set the needle valve for a slow cylinder speed.
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❑ 7. Extend and retract the cylinder and observe its speed in both
extension and retraction. Record below whether the speed is fast or
slow for each direction of motion.
Speed Extending _____________________________ (Fast/Slow)
Speed Retracting _____________________________ (Fast/Slow)
❑ 8.
❑ 9.
❑ 10.
❑ 11.
❑ 12.
You should observe that the cylinder speed is faster during
retraction, because the check valve is bypassing the flow around
the needle valve.
The circuit you have designed duplicates the function of a flow
control valve.
Now try adjusting the needle valve to another flow setting by
closing it 1/4 turn. Then cycle the cylinder and observe the speed
of the cylinder in retraction and extension.
The retract speed should stay the same but the extend speed should
be slower than it was in step 7.
Reduce the relief valve’s pressure setting to minimum and turn off
the power unit.
Reverse the position of the hose ends at the check valve to see
what effect this has on the operation.
Turn on the power unit and increase the relief valve’s pressure
setting to 300 psi / 2070 kPa.
Now extend and retract the cylinder and observe its speed. Notice
the change in the cylinder speed in each direction caused by the
reversed check valve. Observe whether the speed is fast or slow for
each direction of motion.
Speed Extending _____________________________ (Fast/Slow)
Speed Retracting _____________________________ (Fast/Slow)
You should observe that the cylinder speed is faster during
extension because the hoses have been reversed causing the check
valve to be reversed.
❑ 13. Reduce the relief valve’s pressure setting to minimum. Turn off
the power unit and close the shutoff valve.
❑ 14. Move the handle of the DCV back and forth to remove any
pressure in the circuit.
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SEGMENT 2
SELF REVIEW
1. The check valve is a(n) ______ way directional control
valve.
2. Check valves are used to hold prime, avoid pump reversal,
________, and provide back pressure.
3. The direction through a check valve that allows flow is
called ______________ direction.
4. The three types of check valves used in hydraulic systems
are the _________, ___________, and __________ types.
5. The poppet type check valve uses a(n) _________ to hold
the poppet on the seat.
6. A check valve is designed to provide __________ in one
direction only.
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SEGMENT 3
FLOW CONTROL VALVES
OBJECTIVE 7
DESCRIBE THE FUNCTION OF THE FLOW CONTROL VALVE
AND GIVE AN APPLICATION
The flow control valve used in the 850 Series trainer combines a
needle valve and check valve together in one valve body to restrict
flow in one direction and allow free flow in the other direction. A
typical flow control valve is shown in figure 20.
The flow control valve is used with bi-directional actuators to make
the speed in one direction different from the other.
Figure 20. Flow Control Valve with Quick-Connect Fittings
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OBJECTIVE 8
DESCRIBE THE OPERATION OF A FLOW CONTROL VALVE
AND GIVE ITS SCHEMATIC SYMBOL
The flow control valve consists of a body with an inlet and outlet
port, an adjustment screw with a tapered end, an adjustment knob, a
check valve poppet, and a spring, as shown in figure 21.
ADJUSTMENT
KNOB
NEEDLE
VALVE
VALVE
BODY
DIRECTION
OF
CONTROLLED
FLOW
DIRECTION
OF
FREE FLOW
SPRING
POPPET
Figure 21. Construction of a Flow Control Valve
The two symbol techniques used for the flow control valve are
shown in figure 22.
EXPLANATION
SYMBOL
INDICATES
ADJUSTABLE
FLOW
INDICATES
ORIFICE
CONTROLLED
FLOW
FREE
FLOW
CHECK
VALVE
OR
INDICATES
IN SAME
ENVELOPE
(BODY)
Figure 22. Flow Control Valve Symbol with Explanation
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SKILL 3
CONNECT AND ADJUST A FLOW CONTROL VALVE
TO CONTROL SPEED OF AN ACTUATOR
Procedure Overview
In this procedure, you will connect a flow control valve
in a bi-directional actuator circuit to control the actuator
speed in one direction only.
❑ 1. Set up the circuit shown in figure 23.
In this circuit, the flow control valve will control the flow to a
bi-directional motor. Motor speed will be controlled in one
direction and run at full speed in the other direction.
DIRECTIONAL
CONTROL
VALVE
SUPPLY
MANIFOLD
HOSE A
HOSE B
FLOW
METER
SHUTOFF
VALVE
RETURN
MANIFOLD
IN
A
OUT
B
A
B
FLOW
CONTROL
VALVE
MOTOR
Figure 23. Schematic of a Flow Control Valve in a Motor Circuit
❑ 2. If not already done, remove the flywheel from the shaft of the
❑ 3.
❑ 4.
❑ 5.
❑ 6.
motor.
Perform the power unit checkout procedures.
Turn on the power unit and adjust the power unit relief valve to
300 psi/2070 kPa.
Close the flow control valve completely by turning the adjustment
knob fully CW. Then open it 1/2 turn.
Open the shutoff valve.
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❑ 7. Push in on the lever of the DCV to run the motor and hold it. The
motor should run slowly.
As the motor is running, experiment with your ability to control the
speed of the motor by adjusting the flow control valve’s orifice
setting.
As you do this, excess pump flow is being diverted through the
relief valve on the power unit.
Fluid entering the flow control valve in the direction of controlled
flow is forced to flow across the needle valve, as shown in figure
24. It cannot flow across the check valve, because the poppet
blocks flow in that direction. The amount of flow, and therefore,
the speed of the actuator, can then be controlled by adjusting the
opening of the adjustment screw.
ADJUSTMENT KNOB
CONTROLS FLUID FLOW
FLUID
FLOW
IN
POPPET BLOCKS
FLUID FLOW IN
THIS DIRECTION
OUT
MOTOR
TURNING
Figure 24. Flow Control Valve Controlling Flow to a Motor
❑ 8. As the motor is running, adjust the flow control valve setting so
the flowmeter reads 0.5 gpm / 1.9 lpm.
The motor should still be running slowly.
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❑ 9. Now reverse the direction of flow and motor rotation by pulling
the lever of the DCV out.
Observe the flow rate and the speed of the motor. Because the flow
rate through the flow control valve is in the free-flow direction,
full pump flow should be going through the motor causing it to run
at high speed.
Fluid entering the flow control valve in the direction of free flow
can flow in two paths. It can flow across the opening of the
adjustment screw and across the check valve poppet, as shown in
figure 25. Because the poppet of the check valve opens fully to
offer very little resistance, most of the flow will take this path. The
pump flow will then flow to the motor.
IN
OUT
POPPET LETS FLUID
FLOW FREE IN THIS
DIRECTION
FLUID
FLOW
MOTOR
TURNING
Figure 25. Free Flow Operation of a Flow Control Valve
❑ 10. Try to slow down the motor by turning the flow control valve’s
adjustment CW.
You should observe that the flow control valve cannot control or
stop flow in the reverse direction, because its check valve allows
flow to bypass the flow control valve’s variable orifice.
❑ 11. Release the lever of the DCV.
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❑ 12. Perform the following substeps to change the flow control valve’s
❑ 13.
❑ 14.
❑ 15.
❑ 16.
❑ 17.
❑ 18.
❑ 19.
connections.
A. Reduce the power unit relief valve’s setting to minimum.
B. Turn off the power unit.
C. Open the flow control valve 1/2 turn.
D. Reverse the position of the hose ends at the flow control valve
by connecting hose A end to flow control port B and hose B
end to flow control port A. This should allow control of motor
speed in the other direction.
E. Turn on the power unit and set the pressure to 300 psi/2070
kPa.
Push in on the lever of the DCV again and hold it. Observe the
flow rate and speed of the motor.
Because the oil flows freely through the flow control valve, the
motor speed should be fast and the flow meter should indicate full
pump flow.
As the motor is running in this direction, experiment with your
ability to adjust the speed of the motor by adjusting the flow
control valve setting CW.
You should observe that this has no effect.
Open the flow control valve 1/2 turn.
Now reverse the direction of flow and motor rotation by pulling
the lever of the DCV completely outward. Observe the flow rate
and speed of the motor.
You should observe low flow and low speed because flow is being
restricted to the motor.
As the motor is running in this direction, experiment with your
ability to control speed by adjusting the flow control valve’s
orifice setting.
You should now observe that you can control the speed of the
motor in this direction.
Release the lever of the DCV, reduce the power unit relief valve
setting to minimum and turn off the power unit.
Move the handle of the DCV back and forth to remove any
pressure in the circuit.
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OBJECTIVE 9
DESCRIBE THE EFFECT OF ACTUATOR LOAD CHANGES
ON FLOW CONTROL VALVE OPERATION
Unfortunately, setting a flow control valve to a specific flow rate
does not guarantee that the flow will stay constant. One of the factors
that causes the flow through the flow control valve to change is a change
in the actuator load. This happens because the pressure at the relief
valve’s inlet is made up of the pressure drop caused by the flow control
valve, fluid friction, and load. If the load increases, for example, the
pressure at the relief valve’s inlet will increase and cause more flow to
go through the relief valve. This causes the flow to the actuator to
decrease and the actuator slows down. Similarly, if the load decreases,
the speed of the actuator will increase.
In many circuits, the actuator load is fairly constant and some speed
variation is not harmful. For these situations, these valves work very well
and are a very inexpensive solution. However, where loads will change,
a special type of flow control valve called a pressure-compensated flow
control valve must be used. This valve is described in a later LAP.
Activity 3. Effect of Actuator Load Changes on Flow Control
Valve Operation
Procedure Overview
In this procedure, you will demonstrate that the flow
rate through a standard (non-compensated) flow control
valve will change while the valve is controlling flow
whenever the actuator load changes.
❑ 1. Set up the circuit in figure 26.
This circuit uses a flow control valve to control the flow to extend
a cylinder. Gauges B and C will be used to measure the load
pressure across the cylinder. Gauge A will be used to measure the
relief valve pressure.
NOTE
If the load spring is attached to the cylinder load block, you
must remove it before continuing. See LAP 3 (Skill 2) if you do
not remember how this is done.
The load device, as shown in figure 27, should now be attached.
This device will allow you to put a load on the actuator’s rod. By
turning the sockethead screws on the load device CW, you will
increase the load on the cylinder.
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GAUGE A
DIRECTIONAL
CONTROL
VALVE
SUPPLY
MANIFOLD
IN
A
OUT
B
LOCATE TEE'S AT THE
CYLINDER PORTS
EXACTLY AS SHOWN
SHUTOFF
VALVE
A
FLOW
CONTROL
VALVE
B
GAUGE C
RETURN
MANIFOLD
GAUGE B
TEE
LOAD
DEVICE
CYLINDER
Figure 26. Schematic of Circuit for Measuring the Effect of Load
Changes on Flow Control Valve Operation
❑ 2. Using a socket-head wrench (3/16-inch), turn both of the socket
head cap screws on the load device CCW, as shown in figure 27,
until they are both loose. This will remove all load on the cylinder
rod.
Figure 27. Adjusting the Cylinder Load Device
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❑ 3. Perform the power unit checkout procedures.
❑ 4. Turn on the power unit and increase the relief valve setting to 500
psi/3447 kPa.
❑ 5. Open the shutoff valve.
❑ 6. Close the flow control valve completely and then open it 1/2 turn.
WARNING
Keep your hands and fingers away from the load device when
you are operating the cylinder. Do not attempt to make
adjustments while the cylinder is moving.
❑ 7. Extend and retract the cylinder using the DCV to test its operation.
❑ 8. Adjust the flow control valve’s setting so that the cylinder takes
about two seconds to extend. Cycle the cylinder to test the speed
and use a stopwatch to measure the time. Then leave the cylinder
in the retracted position.
❑ 9. Now extend the cylinder again and observe the readings of Gauges
A, B, and C as the cylinder is extending. Record your readings in
the no load row.
LOAD
EXTEND
STROKE
TIME
(seconds)
GAUGE A
PRESSURE
GAUGE B
PRESSURE
GAUGE C
PRESSURE
(psi/kPa)
(psi/kPa)
(psi/kPa)
No Load
Light Load
Heavy Load
❑ 10. Use the following steps to increase the load to a light load of 150
psi/1035 kPa.
A. Turn the load device’s cap screws CW, as shown in figure 27,
about 1/4 turn each.
B. Extend the cylinder again and observe the readings of gauges B
and C. The load across the cylinder is indicated by the pressure
difference between Gauges B and C.
C. Continue to adjust the friction load device by turning the cap
screws until the pressure difference between Gauges B and C is
approximately 150 psi/1035 kPa while the cylinder is
extending. Cycle the cylinder several times, if needed, to make
this adjustment.
D. Leave the cylinder in the retracted position.
You have now set the light load on the cylinder.
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❑ 11. Now extend the cylinder and measure, using a stopwatch, the time
❑ 12.
❑ 13.
❑ 14.
❑ 15.
❑ 16.
required to extend the cylinder under a light load. Also, observe
the pressure readings on Gauges A, B, and C. This is the data for
the light load row of the chart.
Notice how the increased load affects the cylinder’s speed when it
is being controlled by a standard flow control valve.
You should observe that the time to extend is greater even though
the flow control valve’s setting is the same. This is because the
higher load pressure is causing more flow to be diverted across the
relief valve.
Repeat step 10 to change the load on the cylinder to approximately
250 psi/1725 kPa. This is a heavy load.
Extend the cylinder under a heavy load and measure the time to
extend and the pressure gauge readings. Record your data in the
heavy load row of the chart.
You should observe that the cylinder slows down even further.
Leave the cylinder retracted, reduce the relief valve setting to its
minimum, turn off the power unit and close the shutoff valve.
Remove all load from the cylinder rod by turning the adjustment
screws on the load device CCW.
Move the handle of the DCV back and forth to remove any
pressure in the circuit.
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SEGMENT 3
SELF REVIEW
1. The flow control valve is a(n) ________ valve and a(n)
_________ valve in one body.
2. To decrease flow through a flow control valve, turn the
adjuster in the _______ direction.
3. In a circuit where a flow control valve controls cylinder
speed, a drop in the load will cause the cylinder to ________
speed.
4. As controlled flow through a flow control valve increases,
flow through the _________valve decreases.
5. Fluid entering the flow control valve in the __________
flow direction can flow two ways.
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SEGMENT 4
METER-IN AND METER-OUT CIRCUITS
OBJECTIVE 10
DESCRIBE THE OPERATION OF A METER-IN
FLOW CONTROL CIRCUIT AND GIVE AN APPLICATION
This unit has discussed the operation of the needle valve and the
flow control valve without concern to the placement in the circuit.
Although these valves can be placed at either the inlet or the outlet of the
actuator to control actuator speed, the placement of these valves is
important in some applications.
If the flow control valve is placed at the inlet to the actuator, this is
called a meter-in flow control circuit, as shown in figure 28. In this
example, the circuit affects the speed of the cylinder while it extends.
The fluid leaving the other end of the cylinder is allowed to leave
unrestricted.
ROD
EXTENDING
M
DCV
SHIFTED
Figure 28. Metering-In to Control Cylinder Extend Speed
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The meter-in flow control circuit can also be used to control the
speed of the actuator during retraction, as shown in figure 29.
ROD
RETRACTING
M
DCV
SHIFTED
Figure 29. Metering-In to Control Cylinder Retract Speed
The meter-in circuit provides precise control and is a common
method of controlling speed. However, it cannot be used in all
applications. It can only be used to control speeds where the load
opposes the rod movement. Extending the lift cylinder of a crane, as
shown is figure 30, is an example of an opposing load.
CRANE FORCES
ALWAYS ACT
IN THIS
DIRECTION
LIFT CYLINDER
Figure 30. Hydraulic Lift Crane
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In some applications, the load helps the rod movement in one
direction. Retracting the crane’s lift cylinder is an example where the
load helps or aids the movement. The meter-in circuit will not work to
control speed in these applications because the force of the load will tend
to make the cylinder movement "run away."
The meter-in circuit is not normally used with hydraulic motors
because almost all motors have an overrunning (aiding) load.
SKILL 4
CONNECT AND OPERATE A METER-IN
FLOW CONTROL CIRCUIT
Procedure Overview
In this procedure, you will connect a flow control valve
to meter in the flow and demonstrate the operation of this
circuit.
❑ 1. Connect the meter-in flow control circuit shown in figure 31
using the large bore cylinder.
If installed, remove the load spring.
In this circuit, Gauges A and B indicate the pressure drop across
the flow control valve. The flowmeter will measure the flow
through the flow control valve.
SUPPLY
MANIFOLD
IN
OUT
FLOW
METER
IN
A
OUT
B
DIRECTIONAL
CONTROL
VALVE
TEE
A
GAUGE
A
FLOW
CONTROL
VALVE
GAUGE
C
B
RETURN
MANIFOLD
TEE
CONNECT TEE'S
AT THE FLOW CONTROL VALVE
GAUGE
B
LARGE
BORE
CYLINDER
Figure 31. Schematic of a Meter-In Flow Control Circuit
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❑ 2. Perform the power unit checkout procedures.
❑ 3. Perform the following substeps to set up the circuit for testing.
A. Close the flow control valve completely and then open it 1/2
turn. This will cause the cylinder extend speed to slow,
allowing extend times to be easily measured.
B. Turn on the hydraulic power unit.
C. Increase the relief valve setting until Gauge S reads 400
psi/2760 kPa.
D. Open the shutoff valve.
You are now ready to operate the meter-in circuit.
❑ 4. Extend the cylinder and observe the operation of the cylinder using
a meter-in flow control circuit.
You should observe that the cylinder extends at less than full
speed.
❑ 5. Once the cylinder is fully extended, retract the cylinder and
observe the speed of retraction.
You should observe a rapid retraction because flow bypasses
through the check valve.
❑ 6. Perform the following substeps to see how slowly you can get the
cylinder to extend.
A. Close the flow control valve enough to obtain a slow, smooth
speed.
NOTE
You may have to extend and retract the cylinder several times
to get the slowest setting.
You should observe that very slow and smooth cylinder
extension is easily obtained. This would not be the case if using
pneumatics. This is one of the most important features of a
hydraulic system.
B. Record the slowest extend time obtained.
Time to Extend ______________________________(Seconds)
70 to 90 seconds is typical.
❑ 7. Perform the following substeps to experiment with your ability to
control cylinder speed with a meter-in flow control circuit.
A. Adjust the flow control valve so that the flowmeter reads 0.5
gpm/1.9 lpm while the cylinder is extending.
To do this, you will have to make several trial adjustments to
the flow control valve’s setting. Cycle the cylinder after each
adjustment to observe the flowmeter reading.
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B. Once the flow rate is adjusted, extend the cylinder again and
record in the following table the time required to extend. Also,
record the maximum readings of Gauges A, B, and C while the
cylinder is extending.
You should observe that Gauge A indicates a pressure close to
400 psi/2760 kPa because the rest of the pump flow is going
through the relief valve. The pressures at Gauges B and C
should be low because there is no load on the cylinder and the
oil leaves the cylinder unrestricted.
NOTE
You may have to extend and retract the cylinder several times
to obtain each of the readings.
NOTE
Read the pressure gauges as accurately as possible.
METER-IN
FLOW
RATE
(gpm/lpm)
EXTENSION PRESSURE
STROKE
GAUGE A
TIME
(seconds)
(psi/kPa)
PRESSURE
GAUGE B
PRESSURE
GAUGE C
(psi/kPa)
(psi/kPa)
0.5/1.9
/
/
/
0.75/2.9
/
/
/
1.0/3.8
/
/
/
1.25/4.8
/
/
/
C. Observe the flowmeter and Gauge C as you retract the cylinder.
Full pump flow should be going to the cylinder and oil leaving
the cylinder flows through the bypass check valve of the flow
control valve unrestricted.
You should observe low pressure on Gauge C.
D. Repeat substeps A, B, and C for each of the other flow rates
listed in the chart.
You should observe a decrease in extend stroke time as flow
rate to the cylinder increases. Pressure gauge readings should
remain nearly the same.
This exercise shows that you can precisely adjust the speed of
the cylinder using meter-in speed control.
❑ 8. Reduce the relief valve to its minimum setting.
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❑ 9. Install the load spring as shown in figure 32. The load spring will
be placed behind the rod cam so that it simulates the effect of an
aiding load during cylinder extend.
NOTE
The instructions for installing the load spring are given in LAP
3 (Skill 4).
SUPPLY
MANIFOLD
IN
OUT
FLOW
METER
IN
A
OUT
B
DIRECTIONAL
CONTROL
VALVE
TEE
A
GAUGE
A
FLOW
CONTROL
VALVE
GAUGE
C
B
RETURN
MANIFOLD
TEE
CONNECT TEES
AT THE FLOW CONTROL VALVE
GAUGE
B
LARGE
BORE
CYLINDER
LOAD
SPRING
Figure 32. Schematic of Circuit with an Aiding Load During Extend
❑ 10. Close the flow control completely and then open it 1/4 turn.
❑ 11. Increase the relief valve setting until Gauge S reaches 300 psi /
2070 kPa.
You are now ready to observe the operation of a meter-in circuit to
control the speed of an aiding or overrunning load.
❑ 12. Retract and then extend the cylinder to observe its operation using
a meter-in flow control circuit.
You should observe that the cylinder rod jumps suddenly when the
DCV is shifted.
❑ 13. Repeat step 12 several times to observe the operation of a meter-in
circuit with an over-running load. Try several different flow
control settings to see if this has any effect.
You should observe that the meter-in circuit does not provide good
speed control to a cylinder with an over-running load.
❑ 14. Close the shutoff valve, reduce the relief valve to its minimum
setting, and turn off the hydraulic power unit.
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❑ 15. Move the handle of the DCV back and forth to remove any
pressure still in the circuit.
Leave the load spring installed on the cylinder. It will be used in
the next skill.
OBJECTIVE 11
DESCRIBE THE OPERATION OF A METER-OUT
FLOW CONTROL CIRCUIT AND GIVE AN APPLICATION
Another method of controlling flow rate is a meter-out flow control
circuit. This type, shown with a cylinder in figures 33 and 34, controls
speed by restricting the flow of oil leaving the actuator. The fluid
entering the actuator enters unrestricted.
Meter-out circuits control actuator speed well when the load is either
aiding or opposing. This makes the meter-out circuit a more versatile
method than the meter-in circuit.
The meter-out circuit is able to control speed when the load tends to
run away (aiding loads) because it creates a back pressure on the
actuator. This back pressure is able to resist the force of the load. This
back pressure also creates an opposing load at the cylinder or motor to
keep the actuator in control with a solid cushion of fluid. Most fluid
meter circuits use meter-out flow control.
ROD
EXTENDING
DCV
SHIFTED
M
Figure 33. Metering Out to Control Cylinder Extend Speed
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ROD
RETRACTING
DCV
SHIFTED
Figure 34. Metering Out to Control Cylinder Retract Speed
SKILL 5
CONNECT AND OPERATE A METER-OUT
FLOW CONTROL CIRCUIT
Procedure Overview
In this procedure, you will connect a flow control valve
in a meter-out flow control circuit and demonstrate the
operation of this circuit when the load is aiding.
❑ 1. If not already installed, mount the load spring behind the rod cam
and set up the meter-out flow control circuit shown in figure 35.
In this circuit, the flow control valve will control the flow rate only
when the cylinder extends. Gauges A and B indicate the pressure
drop across the valve. The flowmeter indicates the flow rate to the
cylinder. The load spring provides an aiding load during extension.
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GAUGE A
FLOW
CONTROL
VALVE
GAUGE B
SUPPLY
MANIFOLD
IN
OUT
FLOW
METER
IN
A
OUT
B
A TEE
TEE B
RETURN
MANIFOLD
CONNECT TEES
AT THE FLOW CONTROL VALVE
LARGE
BORE
CYLINDER
LOAD
SPRING
Figure 35. Schematic of Meter-Out to Extend Flow Control Circuit
❑ 2. Perform the power unit checkout procedures.
❑ 3. Perform the following substeps with the hydraulic supply.
❑ 4.
❑ 5.
❑ 6.
❑ 7.
A. Turn on the hydraulic power unit.
B. Adjust the relief valve pressure to 300 psi/2070 kPa.
C. Open the shutoff valve.
Close the flow valve completely and then open it 1/2 turn. This
will cause the cylinder speed to be reduced.
Extend the cylinder and observe its operation using a meter-out
flow control circuit with an aiding load.
Observe if the cylinder rod jumps suddenly when the DCV is
shifted or if the movement is smooth and controlled.
You should observe that rod movement is smooth, controlled and
extends at less than full speed. This shows how a meter-out circuit
is better for overrunning loads than a meter-in circuit.
Once the cylinder is fully extended, retract the cylinder. Observe
cylinder speed. Is it still controlled by the flow control valve or
does it bypass through the check valve?
You should observe that it partially retracts at full speed.
Repeat steps 5 and 6 several times to observe the operation of a
meter-out circuit with an aiding load. Try several different flow
control settings to see if this has any effect.
You should observe that cylinder extension is smooth and
controlled.
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❑ 8. Reduce the relief valve pressure to minimum, close the shutoff
valve, and remove the load spring.
❑ 9. Increase the relief valve pressure until Gauge S reads 400 psi /
2760 kPa.
❑ 10. Perform the following substeps to see how slowly you can get the
cylinder to extend.
A. Open the shutoff valve.
B. Close the control valve enough to obtain the slowest, smoothest
speed.
NOTE
You should observe that very slow and smooth cylinder
extension is easily obtained. This would not be the case if using
pneumatics.
C. Record the slowest extend time obtained.
Time to Extend ______________________________(Seconds)
70 to 90 seconds is typical.
❑ 11. Perform the following substeps to experiment with your ability to
set specific cylinder speeds with a meter-out circuit.
A. Adjust the flow control valve so that the flowmeter reads 0.5
gpm / 1.9 lpm while the cylinder is extending. To do this, you
will have to make several trial adjustments to the flow control
valve’s setting. Cycle the cylinder after each adjustment to
observe the extend time.
B. Once the flow is adjusted, extend the cylinder again and record
the time required to extend in the table. Also, record the
readings of Gauges A, B, and S while the cylinder is extending.
You should observe that Gauges A and S read near 400
psi/2760 kPa because the rest of pump flow is going over the
relief valve gauge. Gauge B should be minimum because
during extend it is indicating return pressure.
NOTE
You may have to extend and retract the cylinder several times
to obtain the readings.
NOTE
Record the pressure gauge readings as accurately as possible.
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METER-OUT
FLOW
RATE
(gpm/lpm)
EXTENSION PRESSURE
STROKE
GAUGE A
TIME
(seconds)
(psi/kPa)
PRESSURE
GAUGE B
PRESSURE
GAUGE S
(psi/kPa)
(psi/kPa)
0.5/1.9
/
/
/
0.75/2.9
/
/
/
1.0/3.8
/
/
/
1.25/4.8
/
/
/
C. Retract the cylinder while observing the cylinder speed,
flowmeter indication and Gauge A reading.
The cylinder rod should retract rapidly, because the pump flow
is going across the bypass check to the cylinder. Gauge A
should be at a low pressure.
D. Repeat substeps A, B, and C for each of the other flow rates
listed in the chart.
You should observe a decrease in extend time as flow rate to
the cylinder increases. Pressures should remain close to those
obtained in substeps B and C.
The stroke times obtained should be nearly the same as those
obtained with the meter-in circuit.
❑ 12. Reduce the relief valve to its minimum setting, close the shutoff
valve, and turn off the power unit.
❑ 13. Move the handle of the DCV back and forth to remove any
pressure in the circuit.
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SEGMENT 4
SELF REVIEW
1. ________ flow control circuits are used when the load is
aiding or over-running.
2. Either a meter-in or meter-out flow control circuit may be
used when the load is ________________.
3. Meter-out circuits control actuator speed well when the load
is either _________ or opposing.
4. A meter-in flow control circuit controls speed by controlling
the amount of oil going ________________ the actuator.
5. The meter-in circuit provides precise control and is a
common method of controlling __________.
6. Most motor speed circuits are meter-out because almost all
motors have ________________ loads.
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SEGMENT 5
FLOW CONTROL CIRCUIT DESIGN
OBJECTIVE 12
DEFINE INDEPENDENT SPEED CONTROL
AND GIVE AN APPLICATION
In most cases, an industrial actuator’s speed in each direction must
be adjusted independently of each other. This is called independent
speed control. The reasons for this include:
• Slow Approach / Fast Reset - Machines often require a cylinder to
extend very slowly while it is performing an action. If the retract
stroke is used only to reset the cylinder for the next cycle, it is
desirable to retract at high speed to cut the cycle time.
An example is the metal expander machine shown in figure 36. This
machine requires the cylinders to slowly extend while they are
expanding the metal tube. The cylinder can retract at high speed to
reset for the next part.
• Identical Speeds - Because the rod and cap end areas of a cylinder are
different, a cylinder will naturally extend and retract at different
speeds because the flow rate to the cylinder is the same during
retraction and extension.
Figure 36. Metal Expander Machine with Slow Approach/Fast Reset
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Independent speed control requires two flow control valves. One
valve controls the speed in each direction. These valves can be connected
to provide either meter-in or meter-out speed control.
SKILL 6
DESIGN AN INDEPENDENT SPEED CONTROL CIRCUIT
Procedure Overview
In this procedure, you will design a circuit that will
separately control the speed of an actuator in each
direction.
❑ 1. Complete the circuit shown in figure 37 so that you can control the
speed of the cylinder in each direction using a separate flow
control valve. Draw the two flow control valves so that each valve
provides meter-out flow control.
Label your flow control valves FC1 and FC2. FC1 should control
the extend speed and FC2 should control the retract speed.
SUPPLY
MANIFOLD
IN
A
OUT
B
RETURN
MANIFOLD
DIRECTIONAL
CONTROL
VALVE
LARGE
BORE
CYLINDER
Figure 37. Partial Schematic
❑ 2. Connect your circuit design on the 850 Series trainer.
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❑ 3. Perform the power unit checkout procedures.
❑ 4. Perform the following substeps to set up the circuit for testing.
A. Close both flow control valves completely. Then open each 1/2
turn. This will cause the speed of the cylinder to be slow for
both directions of motion.
B. Turn on the hydraulic power unit.
C. Adjust the relief valve pressure to 400 psi / 2760 kPa.
D. Open the shutoff valve.
You are now ready to demonstrate independent speed control.
❑ 5. Extend and retract the cylinder. Notice whether the speed is
controlled in both directions.
You should observe that the speed is controlled in both directions.
Confirm your design with the data sheet solution. This is a classic
circuit design that designers often use in hydraulic circuits.
❑ 6. Adjust FC 1 to several different settings to test its effect on the
circuit. Extend and retract the cylinder after each new adjustment
and observe the cylinder’s speed.
You should observe that the speed of the cylinder changes for only
one direction of motion when FC 1 is readjusted. Record below
which direction of motion changes.
FC 1 controls _____________________________(Retract/Extend)
You should observe that only the extend speed is affected.
❑ 7. Reset FC 1 to 1/2 turn open.
❑ 8. Now adjust FC 2 to several different settings to test its effect on
the circuit. Extend and retract the cylinder after each new
adjustment and observe the cylinder’s speed.
You should observe that the speed of the cylinder changes for only
one direction of motion when FC 2 is readjusted. This should be
the direction opposite that of FC 1. Record below this direction.
FC 2 controls _____________________________(Retract/Extend)
❑ 9. Reduce the relief valve pressure to minimum, close the shutoff
valve and turn off the power unit.
❑ 10. Move the handle of the DCV back and forth to remove any
pressure in the circuit.
❑ 11. Now design and connect a new circuit that performs the same task
as your circuit in figure 37 except that it uses meter-in speed
control.
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❑ 12. Perform the following substeps to set up the circuit for testing.
A. Close both flow control valves completely. Then open each 1/2
turn. This will cause the speed of the cylinder to be slow for
both directions of motion.
B. Turn on the hydraulic power unit.
C. Adjust the relief valve pressure to 400 psi/2760 kPa.
D. Open the shutoff valve.
You are now ready to demonstrate independent speed control.
❑ 13. Extend and retract the cylinder. Notice whether the speed is
controlled in both directions.
You should observe that the speed is controlled in both directions.
Confirm your design with the data sheet solution. The circuit is
also a classic design that you often see.
❑ 14. Adjust FC 1 to several different settings to test its effect on the
circuit. Extend and retract the cylinder after each new adjustment
and observe the cylinder’s speed.
You should observe that the speed of the cylinder changes for only
one direction of motion when FC 1 is readjusted. Record below
which direction of motion changes.
FC 1 controls _____________________________(Retract/Extend)
You should observe that only the extend speed is affected.
❑ 15. Reset FC 1 to 1/2 turn open.
❑ 16. Now adjust FC 2 to several different settings to test its effect on
the circuit. Extend and retract the cylinder after each new
adjustment and observe the cylinder’s speed.
You should observe that the speed of the cylinder changes for only
one direction of motion when FC 2 is readjusted. This should be
the direction opposite that of FC 1. Record below this direction.
FC 2 controls _____________________________(Retract/Extend)
❑ 17. Reduce the relief valve pressure to minimum, close the shutoff
valve and turn off the power unit.
❑ 18. Move the handle of the DCV back and forth to remove any
pressure in the circuit.
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OBJECTIVE 13
EXPLAIN HOW SPEED CONTROL VALVES CAN BE USED
TO PROVIDE MULTIPLE SPEEDS
In some applications, there is a need to have an actuator operate at
different speeds. An example of this is the rapid approach of a machine
tool to get it into position followed by a slow feed while machining. This
is called a rapid traverse-slow feed. This technique helps increase the
productivity of the machine.
An easy method of providing multiple actuator speeds is to use a
separate speed control valve for each speed and switch to the flow
control valve (speed) desired. This switching is done using a DCV.
Figure 38. Hydraulic Press with Rapid Traverse-Slow Feed
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SKILL 7
DESIGN A TWO-SPEED ACTUATOR CIRCUIT
Procedure Overview
In this procedure, you will design a circuit to provide
two speeds to an actuator as it operates in one direction.
❑ 1. Complete the design of the circuit shown in figure 39 to provide
two-speed control of the motor.
With the DCV in neutral (not shifted), the motor should be already
running at a speed that can be adjusted. This is to be the low speed
part of the circuit.
When the DCV is shifted to the straight arrows condition, the
motor should continue to run but at a higher speed. This higher
speed should also be adjustable.
Label the low speed flow control valve as FC1 and the high speed
flow control valve as FC2.
SUPPLY
MANIFOLD
DCV
MOTOR
IN
A
OUT
B
RETURN
MANIFOLD
FLOW
METER
OUT
IN
Figure 39. Partial Schematic of a 2-Speed Motor Circuit
❑ 2. Set up your circuit on the trainer.
❑ 3. Perform the following substeps to set the speed controls.
A. Close FC1 completely and then open it 1/2 turn.
B. Close FC2 completely and then open it two turns.
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❑ 4. Perform the power unit checkout procedures.
❑ 5. Perform the following substeps with the hydraulic supply.
A. Turn on the hydraulic power unit.
B. Adjust the relief valve pressure to 400 psi / 2760 kPa.
C. Open the shutoff valve.
The motor should start and run at low speed.
❑ 6. Now push in on the handle of the DCV and observe the speed of
the motor.
You should observe the motor running fast.
❑ 7. Release the handle of the DCV.
The motor should return to its slow speed.
❑ 8. Reduce the relief valve to its minimum setting, turn off the power
unit, and close the shutoff valve.
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SEGMENT 5
SELF REVIEW
1. The __________ speed control circuit uses separate flow
control valves to control the speed of an actuator in both
directions.
2. Multiple speed circuits may use flow control valves and
__________ to switch between them.
3. A rapid traverse-slow feed circuit is used to increase
machine ________________.
4. Because the _____ and _____ end areas are different in a
double-acting cylinder, extend and retract times are
different.
5. Retract stroke on a double-acting cylinder is done at high
speed when it is used to _______________ the cylinder for
the next cycle.
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SEGMENT 6
FLOW RATE VS. CYLINDER SPEED
OBJECTIVE 14
DESCRIBE HOW TO CALCULATE THE EXTEND SPEED
OF A HYDRAULIC CYLINDER
The speed of a cylinder depends only on the entering flow rate and
the volume being filled. Therefore, in order to calculate the extend speed,
it is necessary to recognize that the oil flow is causing the piston to be
moved and creating a greater volume inside the cap end of the cylinder.
The rate at which the piston moves depends on the rate at which the flow
of oil can fill the volume of the cap end of the cylinder. The rod speed
(RS) extending is therefore the rate at which the cylinder’s volume is
filled as shown in figure 40. This calculation is made using the following
formula:
FORMULA: EXTEND SPEED OF A CYLINDER
Rod Speed =
Flow Rate
Area
U.S. Customary Units:
Extend Rod Speed (in/min) =
Flow Rate (gpm ) × 231
Piston Area (in 2 )
S.I. Units:
Extend Rod Speed (cm/min) =
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Flow Rate (lpm ) × 1000
Piston Area (cm 2 )
59
VOLUME = R x A
FLOW
RATE OF VOLUME INCREASE = (RS) x A
EXTEND
SPEED (RS)
A
WHERE A = AREA OF PISTON
R
R = LENGTH OF VOLUME
IN CAP END
RS = ROD SPEED
Figure 40. Calculating Extend Speed of a Cylinder
SKILL 8
CALCULATE THE EXTEND SPEED OF A HYDRAULIC
CYLINDER GIVEN ITS SIZE AND A FLOW RATE
Procedure Overview
In this procedure, you will calculate the extend speeds
of the cylinders used in the 850 Series trainer for several
flow rates as well as determine what cylinder size is
needed to produce extend speeds when given the flow
available.
❑ 1. Calculate the piston areas of the two cylinders on the Amatrol
trainer given the following information:
The piston diameter of the large bore cylinder is 1.5 in (3.81 cm)
and the piston diameter of the small bore cylinder is 1.125 in. (2.86
cm).
The formula for the area of a circle is: A = 0.7854 (D2) where D is
the bore diameter.
Large Bore Cylinder Piston Area =__________________ (in2/cm2)
Small Bore Cylinder Piston Area =__________________ (in2/cm2)
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❑ 2. Using the areas from step 1, calculate the extend speeds of the two
cylinders for each of the flow rates shown in the table. Use the
formula for the extend speed of a cylinder.
EXTEND SPEED
FLOW
RATE
(gpm/lpm)
LARGE BORE
CYLINDER
(in/min) / (cm/min)
SMALL BORE
CYLINDER
(in/min) / (cm/min)
0.5/1.9
/
/
0.75/2.9
/
/
1.0/3.8
/
/
1.25/4.8
/
/
❑ 3. Determine the size of a cylinder given the following information:
Extend Rod Speed = 74 in/min / 188 cm/min
Flow rate available = 4 gpm/15.2 lpm
Choose a size to the nearest inch or centimeter. Show your work.
Cylinder Bore Diameter ____________________________(in/cm)
Your calculations should produce a 4 in/10 cm bore diameter.
❑ 4. Determine the flowrate needed to extend a cylinder at a speed of
12 in/min / 30.5 cm/min. The cylinder’s bore size is 6 in / 15.2 cm.
Show your work.
Flowrate Needed = _____________________________(gpm/lpm)
Your calculations should produce a required flow rate of 1.47
gpm/5.53 lpm.
❑ 5. You are an engineer who is assigned to specify the size of a
hydraulic cylinder for a project. Determine the cylinder’s bore size
and the maximum force output of the cylinder given the following
information:
Flowrate available = 26 gpm / 99 lpm.
Extend speed required = 300 in/min / 762 cm/min.
Pressure available = 1500 psi/10,350 kPa.
Specify the cylinder’s bore diameter to the nearest inch and
centimeter. Show your work.
Cylinder Bore Diameter ____________________________(in/cm)
Your calculations should produce a 5 in / 13 cm bore diameter.
Calculate the maximum force output of the cylinder.
Maximum Force Output ____________________________(lbs/N)
Your answer should be 29,453 lbs / 137,378 N.
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OBJECTIVE 15
DESCRIBE HOW TO CALCULATE THE RETRACT SPEED
OF A CYLINDER
The retract speed of a double-acting cylinder is different than the
extend speed because there is less volume to fill. With the rod attached to
the piston, only the annular area need be considered. This means that for
a given flow rate, a cylinder will retract faster than it extends. The
formula to calculate the retract speed is as follows:
FORMULA: RETRACT SPEED OF A CYLINDER
Rod Speed =
Flow Rate
Area
U.S. Customary Units:
Retract Rod Speed (in/min) =
Flow Rate (gpm ) × 231
Annular Area (in 2 )
S.I. Units:
Retract Rod Speed (cm/min) =
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Flow Rate (lpm ) × 1000
Annular Area (cm 2 )
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SKILL 9
CALCULATE THE RETRACT SPEED OF A CYLINDER
GIVEN ITS SIZE AND A FLOW RATE
Procedure Overview
In this procedure, you will calculate the retract speeds
of the cylinders on the hydraulic actuator module and
perform other calculations based on retract speeds.
❑ 1. Calculate the annular area of each cylinder given the following
information:
The large bore cylinder has a piston diameter of 1.5 in. (3.81 cm)
and a rod diameter of 0.44 in. (1.12 cm). The small bore cylinder
has a piston diameter of 1.125 in. (2.86 cm) and a rod diameter of
0.31 in. (0.79 cm).
Large Bore Cylinder Annular Area __________________ (in2/cm2)
Small Bore Cylinder Annular Area__________________ (in2/cm2)
❑ 2. Using the areas from step 1, calculate the retract speeds of the two
cylinders for each of the flow rates shown in the table. Use the
formula for the retract speed of a cylinder.
RETRACT SPEED
FLOW
RATE
(gpm/lpm)
LARGE BORE
CYLINDER
(in/min) / (cm/min)
SMALL BORE
CYLINDER
(in/min) / (cm/min)
0.5/1.9
/
/
0.75/2.9
/
/
1.0/3.8
/
/
1.25/4.8
/
/
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❑ 3. Compare these speeds with those calculated earlier for extend.
You should observe that for the same flow rates, speed of
retraction is faster than the speed of extension. This occurs because
there is less volume to fill during retract.
❑ 4. Determine the size of a cylinder given the following information:
Retract Rod Speed = 110 in/min / 279 cm/min.
Rod Diameter = 1 in / 2.54 cm.
Flow rate available = 3 gpm / 11.4 lpm.
Choose a size to the nearest inch or centimeter. Show your work.
NOTE
Be sure you adjust your calculation to account for the area of
the rod. The diameter you will need to specify is the piston
diameter for the cylinder.
Cylinder Bore Diameter ____________________________(in/cm)
Your calculations should produce a 3 in / 7.6 cm bore diameter.
❑ 5. Determine the flowrate needed to retract a cylinder at a speed of 30
in/min / 76 cm/min.
The cylinder’s bore size is 6 in/15 cm.
The cylinder’s rod size is 1.15 in / 3.8 cm. Show your work.
Flowrate needed _______________________________(gpm/lpm)
Your calculations should produce a flowrate of 3.44 gpm / 12.57
lpm.
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OBJECTIVE 16
DESCRIBE HOW TO CALCULATE THE STROKE TIME
OF A CYLINDER
In many applications you may want to know the amount of time
required for a particular cylinder to complete its stroke given a flow rate.
This calculation is a variation of the rod speed calculation. It is the
formula for rod speed divided into the total stroke length as follows:
Cylinder Stroke Time =
Stroke Length
Rod Speed
Since rod speed is equal to flow rate ÷ cylinder area, the formula is
as follows:
FORMULA: CYLINDER STROKE TIME
Cylinder Stroke Time =
Area × Stroke
Flow Rate
U.S. Customary Units:
Stroke Time (sec) =
Area (in 2 ) × 60 × Stroke (in )
Flow Rate (gpm ) × 231
S.I. Units:
Stroke Time (sec) =
Area (cm 2 ) × 60 × Stroke (cm )
Flow Rate (lpm ) × 1000
NOTE
Where area is either the piston area for extend or the annular
area for retract.
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SKILL 10
CALCULATE THE CYLINDER STROKE TIME
GIVEN ITS SIZE AND A FLOW RATE
Procedure Overview
In this procedure, you will be using the 850 Series
cylinders again. You will then compare these calculations
with the actual measurements made in Skill 4.
❑ 1. Using the areas calculated previously, calculate the extend stroke
times of the two 850 Series cylinders for each of the flow rates
shown in the following table. Use the formula for cylinder stroke
time.
The stroke of the large bore cylinder is 4.0 in (10.2 cm) and the
stroke of the small bore cylinder is 6.0 in (15.2 cm).
EXTEND STROKE TIME
FLOW
RATE
(gpm/lpm)
LARGE BORE
CYLINDER
(seconds)
SMALL BORE
CYLINDER
(seconds)
0.5/1.9
0.75/2.9
1.0/3.8
1.25/4.8
RETRACT STROKE TIME
FLOW
RATE
(gpm/lpm)
LARGE BORE
CYLINDER
(seconds)
SMALL BORE
CYLINDER
(seconds)
0.5/1.9
0.75/2.9
1.0/3.8
1.25/4.8
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❑ 2. Now calculate the retract stroke times for the two cylinders for
each of the flow rates shown in the table. Use the formula for
cylinder stroke time.
❑ 3. Compare the retract and extend stroke times.
_____________________________________________________
_____________________________________________________
You should observe that at the same flow rates, retract stroke times
are shorter than extend stroke times.
❑ 4. Now compare the large bore cylinder calculated stroke times
during extend with those obtained in skill 4. Are they reasonably
close?
______________________________________________(Yes/No)
You may find the stroke times obtained in Skill 4 quite different
than the calculated values because of timing and flow meter
inaccuracies. Generally they should agree.
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SEGMENT 6
SELF REVIEW
1. To calculate the annular area of a cylinder you must know
the piston and _______________ diameters.
2. The extend speed of a cylinder depends on the entering flow
rate and the _______________ being filled.
3. For a given flow rate, a double-acting cylinder will retract
_______________ than it extends.
4. To calculate cylinder stroke time, you need to know piston
area, flow rate, and stroke _______________.
5. For a given flow rate, increasing the cylinder rod diameter
will __________ retraction speed.
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