HYDRAULIC SYSTEMS TRAINING
Presented by: Scott Levy
Date
Introduction to Hydraulic Systems
What are hydraulics?
Answer – The study of the mechanical properties of fluids
What is Fluid Power?
Answer – The use of fluid motion under pressure to transfer power & energy from a
source to a sink (receptor).
Commercial Definitions:
Hydraulics – The transmission of power from a power generation source to a sink using
an engineered incompressible hydraulic fluid for the sake of creating leverage or
motion.
Pneumatics - The transmission of power from a power generation source to a sink using
pressurized air (compressible) as the fluid for the sake of creating leverage or motion.
THIS COURSE WILL ADDRESS HYDRAULIC FLUID POWER
2
Basic Hydraulic Fluid Principles
Elements of Fluid Mechanics
Fluid Flow = Q
Volumetric rate gal/hour, L/min
Fluid Pressure = P
Force per square area Lbs/sq in, Kg/sq m
Fluid Velocity = V
Distance over time ft/sec, m/sec
Fluid Temperature = T
°F or °C
Fluid Viscosity = ν
Fluid resistance to flow cSt (centistokes)
3
Basic Hydraulic Fluid Principles
Fluid Mechanics Relationships
Flow – Velocity
Q= A * v
Where Q= Volumetric Flow Rate, A= Cross sectional Area & v= Fluid Velocity
Fluid flow in a system is additive
Bernoulli’s Law for incompressible fluids
H = z + p/ρg + v2/2g (fluid is flowing with a significant difference in height between
source & sink)
Where H=total head pressure, v= fluid velocity, g= force of gravity, z= the height of the fluid source, p=fluid
pressure & ρ=fluid density
p0 = p + v2/2 (fluid height is insignificant)
Where p0 = total system pressure, p= static pressure v= flow velocity
4
Basic Hydraulic Fluid Principles
Hydraulic Fluid Power
Fluid power depends on a viscous fluid flowing under pressure from a sink to a
source. The systems efficiency is dependent on fluid density, temperature and
pressure loss due to decreased fluid velocity.
Gravity
Change in
Temperature
Source
Fluid Flow
Sink
Creates
Pressure
Viscous Fluid
Has Velocity
Turns fluid pressure /
energy into leverage
5
Basic Hydraulic Systems Overview
Typical Lift / Ram Circuit (mobile or industrial – open center system)
Cylinder
Motion
Relief
Valve
Control
Valve
Cylinder
Pump
Filter
Tank
Cooler
6
Basic Hydraulic Systems Overview
Typical Motor Power Circuit (mobile – closed center system)
EH Servo
Control Valve
Hydraulic
Motor
Blower
Fan
Joystick
Variable
Pump
Filter
Tank
Cooler
7
Hydraulic Motors
Hydraulic Motors Overview
Purpose
A hydraulic motor converts hydraulic energy from pressure into rotary motion and
torque to drive an implement or system.
Types
Fixed positive displacement – gear, piston, geroter / geroler & vane types
 Variable positive displacement – piston

Typical Applications
Wheel Motors – drive mobile equipment wheels (skid steers, tractors, lifts)
 Fan Drives – hydraulic fan drives (engine cooling, industrial equipment, drive train cooling,
gen sets, grain driers)
 Industrial Machinery – (conveyers, machine tools, cutters, cranes, augers, winches)
 Agricultural Equipment – Harvesters, Trenchers, Lawn Mowers, Forestry Equipment

8
Hydraulic Motors
Fixed Positive Displacement Motors
Motor displacement is fixed
Torque is proportional to inlet pressure
Speed is proportional to flow rate
Regulate torque and speed with either valves, variable displacement pump or pump speed.
Gear Motors
Inlet flow / pressure rotates a gear set causing the output shaft to rotate and create torque
 Advantages







Low cost – initial and rebuild
Good availability / many suppliers
Cast iron motors have high pressure capability
Tolerant to contamination
Compact - desirable packaging
Disadvantages


Lower efficiency compared to other types
Lower torque per unit displacement compared to piston or Geroter / Geroler types
9
Hydraulic Motors
Fixed Positive Displacement Motors
Fixed Displacement Piston Motors
Fixed Displacement
Radial Piston Motor

Axial Piston, Radial Piston & Bent Axis Types

Swash plate is fixed on an angle to achieve a specified displacement

Number & size of pistons in rotating group determine flow, torque and speed capabilities

Advantages

High efficiency / Performance

Higher torque capability per unit displacement

Radial type packages well for wheel
motor applications

Fixed Displacement Bent
Axis Piston Motor
Fixed Angle Swash Plate
Bent axis type available for improved
Piston Rotating Group
packaging


Good serviceability
Disadvantages

Higher cost

Not as tolerant to contamination
Fixed Displacement
Axial Piston Motor
10
Hydraulic Motors
Fixed Positive Displacement Motors
Fixed Displacement Vane Motors

Fluid flow over vanes produce rotational speed and torque

High speed and pressure capability

Number & area of vanes determine flow, torque and speed capabilities

Advantages


High efficiency / Performance

Higher speed capacity

Reliability & durability

Forward or reverse rotation

Superior cold start performance

Good power output per motor size
Disadvantages

Lower torque capability

Higher cost than gear motors
11
Hydraulic Motors
Fixed Positive Displacement Motors
Fixed Displacement Geroter / Geroler Motors

Spool valve, disc valve & valve in star types

Low speed and high torque capability

Works on the “Orbit Principle” – star, drive and output shaft

Gerotor & Geroler have similar performance characteristics for equal frame sizes. In the Geroler type,
the drive gear rides on roller bearings in the star for reduced friction, improved mechanical efficiency and
useful life.

Advantages


High efficiency

Higher torque capacity

Reliability & durability – only three main components

Compact with high power density

Can be connected in series with same pump source

High systems pressure capability

Low speed constant with change in load
Disadvantages

No high speed applications

High cost than other motors
12
Hydraulic Motors
Variable Positive Displacement Motors
Variable Displacement Piston Motors
Variable Displacement
Radial Piston Motor

Axial Piston, Radial Piston & Bent Axis Types

Swash plate angle is variable – manual, hydraulic, EH or electric control

Number & size of pistons in rotating group determine flow, torque and speed capabilities

Advantages

High efficiency / Performance

Higher torque capability per unit displacement

Radial type packages well for wheel
Variable Displacement
Axial Piston Motor
motor applications

Bent axis type available for improved
packaging


Good serviceability
Disadvantages

Higher cost

Not as tolerant to contamination
13
Hydraulic Motors
How to Choose & Size a Hydraulic Motor
Step 1 – Document Motor Requirements












What is the application (wheel drive, fan, auger, winch, machine tool, turf care, etc.)
Space requirements - packaging
What torque is required for driving the application component?
What hydraulic system pressure is available to the motor?
What hydraulic system flow is available to the motor?
What speed range is required for the motor?
Does the motor have to stall or reverse direction?
What is the hydraulic oil cleanliness levels?
What are the cost factors?
How many motors will be run in series off of the same source?
What is the ambient temperature range of operation?
What hydraulic fluid will be used?
Step 2 – Choose the Motor Type
Fixed or variable displacement?
 If fixed displacement – use the motor type selection chart to determine which type of fixed displacement
motor best meets the requirements.

14
Hydraulic Motors
How to Choose & Size a Hydraulic Motor
Fixed Motor Type Selection Chart
Selection Criteria
Low Cost
High Pressure
High Speed / Low Torque
Gear Motor
Piston Motor
Gerotor / Geroler Motor
X
X
X (cast iron)
X
X
X
Low Speed / High Torque
X
X
X
High Efficiency
X
High Reliability / Durability
X
X
X
X
Superior Cold Start Performance
X
Availability
X
Compact Size / Displacement
X
Large Displacements
X
X
X
X
X
X
Wide Range of Displacements
X
Tolerant to Contamination
X
Serviceability
X
Bidirectional
X
Motors connected in series w/ one pump
Vane Motor
X
X
X
X
X
15
Hydraulic Motors
How to Choose & Size a Hydraulic Motor
Step 3 – Determine Motor Displacement

How much max horsepower or torque is required to drive the devise?
Torque (in-lbs) = 63024 Horsepower / Speed (rpm)

What max displacement is required?
Displacement (cubic in/rev) = 2π* Torque (in-lbs) / Δ Pressure (psi)* Mechanical Efficiency (%)
Mechanical efficiency varies from 80-90% depending on the type of motor.

What flow is required at the motor?
Flow (gpm) = Motor Displacement (cubic in / rev)* Speed (rpm) / 231* Volumetric Efficiency (%)
Volumetric efficiency varies from 85-95% depending on the type of motor.
Step 4 – Determine the motor that meets the requirements

Find a supplier that makes a motor of the type and size determined

Determine the best model motor to meet all or as many of the requirements for the
application that is at least equal to or larger than the displacement calculated.

Compare the selected motor specifications to the motor requirements and qualify it for the
application.

Recalculate the motor torque and flow with the selected motor’s specs to ensure the torque
and system flow requirements are satisfied.
16
Hydraulic Motors
How to Choose & Size a Hydraulic Motor
Motor Sizing Example
A hydraulic motor is needed to power a blower fan for a combine separation system. The fan
speed will vary from 0 to 1500 rpm and the fan requires 15 hp at max speed and load
conditions. The system pump supplying flow is a variable displacement axial piston pump with
a max flow of 30 gpm. What type of motor and displacement will satisfy these requirements?
Requirements:
•
•
•
•
•
•
•
•
Pressure available at the motor inlet = 2000 psi
Max pressure for motor return to tank = 100 psi
Clockwise rotation only
Only one motor in the system
System is unfiltered
Low cost is important
Ambient temp range 0 °F to 110 °F.
Hydraulic fluid – Hydraulic Oil w/viscosity at 15 cST
normal operation, 10 cST min
Motor Type – See selection chart
Gear type is best selection
Reasons – fixed displacement, low cost, tolerant to contamination in an unfiltered system & low pressure.
17
Hydraulic Motors
How to Choose & Size a Hydraulic Motor
Fixed Motor Type Selection Chart
Selection Criteria
Low Cost
High Pressure
High Speed / Low Torque
Gear Motor
Piston Motor
Gerotor / Geroler Motor
X
X
X (cast iron)
X
X
X
Low Speed / High Torque
X
X
X
High Efficiency
X
High Reliability / Durability
X
X
X
X
Superior Cold Start Performance
X
Availability
X
Compact Size / Displacement
X
Large Displacements
X
X
X
X
X
X
Wide Range of Displacements
X
Tolerant to Contamination
X
Serviceability
X
Bidirectional
X
Motors connected in series w/ one pump
Vane Motor
X
X
X
X
X
18
Hydraulic Motors
How to Choose & Size a Hydraulic Motor
Motor Sizing Example Continued
Theoretical Motor Displacement Calculation
•
•
•
Torque (in-lbs) = 63024 Horsepower / Speed (rpm)
Torque = 63024 (15 hp) / 1500 rpm = 630 in-lbs
Δ Pressure (psi) = Max systems pressure @ inlet – Max motor return to tank pressure
Δ Pressure = 2000 psi – 100 psi = 1900 psi
Displacement (cubic inch / rev) = 2π* Torque (in-lbs) / Δ Pressure (psi)* Mechanical Efficiency (%)
Gear pump mechanical efficiency = 85%
Displacement = (2π * 630 in-lbs) / (1900 psi * 0.85) = 2.45 cubic in/rev or 40.1 cc/rev
Gear pump supplier chosen is Sauer Danfoss Group 3 frame size 44
•
Specs vs. Requirements
Requirement / Spec
Requirement
Specification
Displacement (cubic in / rev)
2.45
2.69
Max speed (rpm)
3000
1500
Min speed (rpm)
800
800
Rated pressure (psi)
3625
2000
35
30
Theoretical Flow @ max speed (gpm)
19
Hydraulic Motors
How to Choose & Size a Hydraulic Motor
Motor Sizing Example Continued
Verify actual motor torque
Torque (in-lbs) = Δ Pressure (psi)* Mechanical Efficiency (%) * Displacement (cubic in/rev) / 2π
 Torque = (1900 psi * 0.85 * 2.69) / 2π = 691 in-lbs > 630 in-lbs
Verify actual motor flow
Flow (gpm) = Motor Displacement (cubic in / rev)* Speed (rpm) / 231* Volumetric Efficiency (%)
Volumetric Efficiency = 88%
Flow = (2.69 cubic in/rev * 1500 rpm) / (231 * 0.88) = 19.8 gpm < 30 gpm available at the pump.
THE PUMP SELECTED MEETS ALL THE REQUIREMENTS
20
Hydraulic Cylinders
Hydraulic Cylinders Overview
Purpose
A hydraulic cylinder converts hydraulic energy from pressure into linear motion and
force to actuate, move or lift an implement or object.
Suspension Strut
Types

Dual Acting / Single Acting

Multi-stage Telescoping

Pressurized struts – Mobile Applications

Head & Cap Arrangements
Cylinder
Cut Away
•
Welded – Medium duty applications / size
•
Threaded – Light duty applications / size
•
Bolted – Heavy duty applications / size
Telescoping
Cylinder
Threaded Head
Cylinder
Welded
Cylinder
Bolted
Cylinder
21
Hydraulic Cylinders
Hydraulic Cylinders Overview
Typical Applications

Construction Equipment – (implements, dump trucks, suspension struts, stabilizers, steering systems)

Lifts – (scissors lifts, aerial lifts, cranes, fork lifts, lift gates)

Industrial Machinery – (presses, rams, loading docks, injection molding machines)

Agricultural Equipment – (tractor implements, bailers, combine heads, sprayers)

Mining Equipment – (hoist, bucket, suspension struts, steering system, grader blades)
22
Hydraulic Cylinders
Hydraulic Cylinders Overview
Single vs. Dual Acting Cylinders


Single acting cylinder only actuates the rod
•
The rod extends under pressure and contracts under force or weight
•
Typically used in applications where load is lifted hydraulically and gravity returned
•
A spring in the system can be used to achieve contraction
Dual acting cylinder actuates the rod and the head ends
•
Both extension and contraction occur under hydraulic pressure
•
Typically used in applications where motion is not in the direction of gravity
Single Acting Cylinder
Dual Acting Cylinder
23
Hydraulic Cylinders
Hydraulic Cylinders Overview
Typical Cylinder Construction

Barrel or body

Rod

Piston & Seal

Rod Gland
Head
 Cap
 Position Sensor

Head
Rod
Rod
Gland
Barrel
Position
Sensor
Piston
Cap
24
Hydraulic Cylinders
How to Choose & Size a Hydraulic Cylinder
Step 1 – Document cylinder requirements












What is the application (lift, press, steering, hoist, implement, ram, crane etc.)
Space requirements – packaging & end attachments
What is the max collapsed length
What is the max extended length
What max force or weight is necessary to actuate the attached object?
What hydraulic system pressure is available to the cylinder?
What hydraulic system flow is available to the cylinder?
How many cylinders will be used to move the load
What max time is required to go from min length to max extended length?
What are the cost factors?
What is the ambient temperature range of operation?
What hydraulic fluid will be used?
Step 2 – Choose the cylinder type
Dual or Single Acting?
 Single Stage or Multiple Stage Telescoping?

25
Hydraulic Cylinders
How to Choose & Size a Hydraulic Cylinder
Step 3 – Determine cylinder bore size

Force = Required Force / # Cylinders

Cylinder Bore (in) = [.7854 * Force (lbs) / Pressure (psi)]

This is the minimum bore size required. To decrease the time to fully extend the cylinder,
the bore size can be increased.

Find a Cylinder of the type chosen with the next larger bore size available
½
Step 4 – Determine if the flow rate required for max extension .
 Flow Rate (gpm) = Fluid Velocity (ipm) * Cylinder Piston Area (in) * 0.00433
 Cylinder Piston Area = π * [Cylinder Bore (in) / 2] 2
 Fluid Velocity (ipm) = [Extended Cylinder Stroke (in)] / [Max Extension Time (sec) / 60]
 Is Flow Rate equal to or less than the required flow rate? If not, the cylinder bore size has to
be increased to ensure the max time to full extension is satisfied within the flow rate
available.
Step 5 – Determine the piston rod diameter & column size
 Determine the column strength factor from Table 1.1
 Corrected Length = Actual Stroke * Column Strength Factor
 Cylinder Thrust (lbs) = Max System Relief Pressure (psi) * Cylinder Piston Area
26
Hydraulic Cylinders
How to Choose & Size a Hydraulic Cylinder
Step 5 – Determine the piston rod diameter & column size continued

Determine the appropriate piston rod diameter
using Table 1.2

Determine the stop tube length if necessary


Internal stops are sometimes required to limit rod
stroke to prevent rod buckling
Stop Tube Length (in) =
[Corrected Length – 40 in] / 10
27
Hydraulic Motors
28
Hydraulic Cylinders
How to Choose & Size a Hydraulic Cylinder
Step 6 – Choose the type of cylinder ends for attachment
Step 7 – Determine a cylinder that meets the requirements

Find a supplier that makes a cylinder of the type and size determined

Determine the best model cylinder to meet all or as many of the requirements for the
application that is at least equal to or larger than the bore and rod diameter calculated.

Compare the selected cylinder specifications to the cylinder requirements and qualify it for
the application.

Recalculate the cylinder load capability and time for full extension with the selected
cylinder’s specs to ensure that these requirements are satisfied.
29
Hydraulic Cylinders
How to Choose & Size a Hydraulic Cylinder
Cylinder Sizing Example
A cylinder is needed to lift and lower a dump truck bed. The design calls for two cylinders.
The maximum load that the cylinders have to lift is 58,350 Lbf. The maximum stroke is 70
inches. The maximum time to fully extend the cylinders into the full dump position is 12
seconds. The system relief pressure is set to 2400 psi and the max available flow rate is 25
gal/min. The empty dump bed weight is not enough to fully retract the cylinder.
Requirements:
•
•
•
•
•
•
Max fully extended length – 125 inches
Max fully retracted length – 42 inches
Clevis Pivot Mount
System is filtered
Ambient temp range 0 °F to 110 °F.
Hydraulic fluid – Hydraulic Oil w/viscosity at
15 cST normal operation, 10 cST min
Cylinder Type
Telescoping dual acting cylinder is chosen
Reason – the fully extended length is more than ½ the
fully retracted length and hydraulic pressure is needed to fully lower the dump bed.
30
Hydraulic Cylinders
How to Choose & Size a Hydraulic Cylinder
Cylinder Sizing Example Continued
Cylinder Bore Size
 Force
= Required Force / # Cylinders = 58,350 lbs / 2 Cylinders = 29,175 Lbs
½
Cylinder Bore (in) = [.7854 * Force (lbs) / Pressure (psi)]
½
Cylinder Bore = [.7854 * 29175 / 2400] = 3.09 inches
Standard multistage cylinder has bores – 4.5” 1rst stage, 3.5” 2nd stage & 2.5” 3rd stage and is capable of
supporting up to 30,000 Lbs static load.
Determine if the flow rate required for max extension.
Cylinder Piston Area = π * [Cylinder Bore (in) / 2] 2
2
Stage 1 piston Area = π * [4.5 (in) / 2] = 15.9 sq in (largest section)
Fluid Velocity = [Extended Cylinder Stroke (in)] / [Max Extension Time (sec) / 60]
Fluid Velocity = [ 70 in ] / [12 / 60] = 350 in / min
Flow Rate (gpm) = Fluid Velocity (ipm) * Cylinder Piston Area (sq in) * 0.00433
Flow Rate = 350 in/min * 15.9 sq in * 0.00433= 24.1 gal / min < 25 gal / min
Determine the piston rod diameter & column size
From Table 1.1 the Column Strength Factor = 2.0
31
Hydraulic Cylinders
How to Choose & Size a Hydraulic Cylinder
Cylinder Sizing Example Continued
Determine the piston rod diameter & column size
 From Table 1.1 the Column Strength Factor = 2.0
 Corrected Length = Actual Stroke * Column Strength Factor = 70 in * 2.0 = 140 in
 Cylinder Thrust (lbs) = Max System Relief Pressure (psi) * Cylinder Piston Area
Cylinder Thrust = 2400 psi * 15.9 sq in = 38,160 lbs
Use Table 1.2 to determine the minimum rod diameter
Piston Rod Diameter = 4.5 in
Corrected Length =140 in
Thrust Load =38,160 Lbs
Stop Tube Length (in) = [Corrected Length – 40 in] / 10 = [140 -40] / 10 = 10 in
Cylinder ends – Clevis Pivot Mount
32
Hydraulic Cylinders
How to Choose & Size a Hydraulic Cylinder
Cylinder Sizing Example Continued
Determine a cylinder that meets the requirements

The supplier chosen is Prince – PMC/SAE 62 a 3-stage telescoping cylinder with 5”x4”x3” rod sizes and
5.5”x4.5”x3.5” bore sizes.
Requirement / Spec
Requirement
Specification
Minimum Bore Size (in)
3.09
5.5 / 4.5 / 3.5
Minimum Rod Size (in)
4.5
6/5/4
Max extended Load (lbs)
38,160
50,000 lbs
Max Closed Length (in)
42
38.58
Max Extended Length (in)
125
146.78
33
Hydraulic Cylinders
How to Choose & Size a Hydraulic Cylinder
Cylinder Sizing Example Continued
Determine a cylinder that meets the requirements

Cylinder time to full extension

Recalculate the cylinder load capability and time for full extension with the selected cylinder’s specs to
ensure that these requirements are satisfied.
34
Thank you.
35