APPLIED HYDRAULICS AND PNEUMATICS
Unit I
1. Define fluid power.
Fluid power is energy transmitted and controlled by means of a pressurized fluid, either
liquid or gas. The term fluid power applies to both hydraulics and pneumatics. Hydraulics uses
pressurized liquid, for example, oil or water; pneumatics uses compressed air or other neutral
gases. Fluid power can be effectively combined with other technologies through the use of
sensors, transducers and microprocessors.
2. State Pascal’s law with an industrial example.
Pascal's Law expresses the central concept of fluid power: "Pressure exerted by a
confined fluid acts undiminished equally in all directions."
An input force of 10 pounds (44.8 N) on a 1-square-inch (6.45 cm2 ) piston develops a
pressure of 10 pounds per square inch (psi) (68.95 kN/m2 or 68.95 KPa) throughout the
container. This pressure will allow a 10-square-inch piston to support a 100-pound (444.8 N)
weight. The forces are proportional to the piston areas.
3. Compare Hydraulic & Pneumatic system.
4. Why are the hydraulic system is preferred for heavy work than pneumatic
system
The favourable difference in power required to compress the liquid and the quantum of
force delivered at the work end make hydraulic systems preferred over pneumatic
system
for
heavy
work.
For the same work,pneumatic system needs more area of compression, the heat
generated is higher and the ratio of power(pressure) input to that of output is also less in
pneumatic systems.
5. Why water is not used as hydraulic fluid in fluid power systems
Water is not used in fluid power system because it corrodes, encourages growth of
bacteria, easily evaporates and gets contaminated easily, has poor lubricity, viscosity and prone
to more leakage. So we chose petroleum based mineral oil as a medium in hydraulics.
PART B
1. List the field of application where fluid power can be used more effectively than any
power sources. Explain in short.,
Any media (liquid or gas) that flows naturally or can be forced to flow could be used to
transmit energy in a fluid power system. The earliest fluid used was water hence the name
hydraulics was applied to systems using liquids. In modern terminology, hydraulics implies a
circuit using mineral oil. Figure 1-1 shows a basic power unit for a hydraulic system. (Note that
water is making something of a comeback in the late '90s; and some fluid power systems today
even operate on seawater.) The other common fluid in fluid power circuits is compressed air.
As indicated in Figure 1-2, atmospheric air -- compressed 7 to 10 times -- is readily available
and flows easily through pipes, tubes, or hoses to transmit energy to do work. Other gasses,
such as nitrogen or argon, could be used but they are expensive to produce and process.
Hydraulic power unit
Of the three main methods of transmitting energy mechanical, electrical, and fluid fluid
power is least understood by industry in general. In most plants there are few persons with
direct responsibility for fluid power circuit design or maintenance. Often, general mechanics
maintain fluid power circuits that originally were designed by a fluid-power-distributor
salesperson. In most facilities, the responsibility for fluid power systems is part of the
mechanical engineers' job description. The problem is that mechanical engineers normally
receive little if any fluid power training at college, so they are ill equipped to carry out this duty.
With a modest amount of fluid power training and more than enough work to handle, the
engineer often depends on a fluid power distributor's expertise. To get an order, the distributor
salesperson is happy to design the circuit and often assists in installation and startup. This
arrangement works reasonably well, but as other technologies advance, fluid power is being
turned down on many machine functions. There is always a tendency to use the equipment
most understood by those involved.
Pneumatic power arrangement
Fluid power cylinders and motors are compact and have high energy potential. They fit
in small spaces and do not clutter the machine. These devices can be stalled for extended time
periods, are instantly reversible, have infinitely variable speed, and often replace mechanical
linkages at a much lower cost. With good circuit design, the power source, valves, and
actuators will run with little maintenance for extended times. The main disadvantages are lack
of understanding of the equipment and poor circuit design, which can result in overheating and
leaks. Overheating occurs when the machine uses less energy than the power unit provides.
(Overheating usually is easy to design out of a circuit.) Controlling leaks is a matter of using
straight-thread O-ring fittings to make tubing connections or hose and SAE flange fittings with
larger pipe sizes. Designing the circuit for minimal shock and cool operation also reduces
leaks.
2. Describe the working of an External gear pump with a diagram
A gear pump comes under the category positive displacement pump which has a
continuous delivery rotary pump. With the help of gear meshing, mechanical energy is
converted into fluid energy and this creates void suction. Space which is in between the gear
meshing pull in the high-level of viscous liquids by letting them flow towards the wall surface and
then to the output. This pump works effectively for an extended level of viscous liquid like oil
because it does not need any priming.
Gear Pump Design
In general, a gear pump is designed either with two or more rotational gears internal to the
casing section having more tolerance. To allow correct fluid transmission, inlet and outlet
positions are made with proper casing. Depending on the casing construction, a gear pump is of
two types. And they are


Internal gear pumps
External gear pumps
Choosing of the gear pump is based on the essential factors. In the case of these pumps, a
liquid displacement per each gear teeth revolution is known by:
Q = ʃ0zt0Vndt
Where flow fluctuation (ŋ) = Vmax – Vmin
And here ‗Q‘ corresponds to fluid displacement
‗Z‘ corresponds to the number of associated teeth
‗Vn‘ corresponds to the liquid flow rate
t0‘ corresponds to the time taken for teeth revolution
‗Vmax‘ and ‗Vmin‘ correspond to the maximum and minimum flow rates
‗Vav‘ corresponds to the average flow rate
Working Principle
The gear pump working principle can be explained as follows:
When there is a revolution of toothed wheels inside of the casing section, air will get wedged in
between and throughout the teeth which creates space. This shows a result of a positive up
direction lift of the liquid on the way to the suction pump. The pump continues to pull in the air
until it initiates to receive liquid through the inner section.
The liquid will be pulled into it at the level of atmospheric pressure; prior to being trapped inbetween the space of two wheels. Gradually the viscous liquid will be pulled in the direction of
output and then pulled towards the out. The pump functions effectively also in the inactive state
but operates more actively when it got primed in before.
Added protection in the scenario of valve relieving is fitted in the gear type revolving pump so as
to expel any kind of destruction either for the pipeline or pump. The relieving valve will decrease
the additional pressure during emergency thus safeguarding the entire equipment.
Applications
The gear pump applications are stated as below:
Mostly, gear pumps are employed for an extended level of viscous liquids like resins, oil,
foodstuffs, and paints.


These are utilized in the applications where precise dosing is necessary.
As the gear pump output is not much influenced by pressure, it can be even applied in
the applications where there is an unbalanced supply.
The classification of gear pumps also have their specific applications:
External Gear Pump Applications

Chemical blending and compounding





Used in lube and fuel oils
Polymers and solving agents
Caustic and acidic fluids
Hydraulic, farming and engineering applications
Polymer metering and chemical extracts
Gear Pump Advantages and Disadvantages
The advantages are




Streamlined maintenance
Minimally susceptible to cavitation‘s
Manageable results
Manage a wide range of viscous fluids
The disadvantages are


Produces loud sound at the time of gears interlocking
Fluids need to free from abrasives
3. What are the factors to be considered for selecting hydraulic pump?
1. Process Liquid Properties
Below are process liquid properties that must be considered before selecting a pump.







Liquid viscosity
Temperature
Specific gravity
Vapor pressure
Solids present & concentration
Shear sensitive
Abrasive or Non-abrasive
2. Materials of Construction
What materials of construction are compatible with the process liquid or any other liquids
the pump might come into contact with? Chemical compatibility charts are available to help you
identify the most appropriate materials of construction for the pump.
3. Is the Pump Critical to Plant Operation?
In critical applications, where downtime is NOT an option, more expensive, heavy-duty
pumps with special features can be chosen. If pumps can be removed from service for
maintenance, less expensive options could be considered.
4. Pump Inlet Conditions
System Net Positive Suction Head (NPSH) available is calculated by knowing pump inlet
pressure and liquid vapor pressure. Always make sure NPSHA exceeds pump Net Positive
Suction Head (NPSH) required.
5. Pump Environment
If your pump will be outside, special construction or installation considerations may need
to be made for freezing temperatures. If the environment is hazardous, contains explosive
vapors or dust, special motor features will be required. These are just a few examples of
environmental conditions to consider.
6. Power Source Availability
The most common power source in the United States is 115-230 Volts/60 Hertz/1-phase
or 230-460 Volts, 60 Hertz/3-phase. Special motors can be specified for operation outside of the
United States or by using DC batteries. Compressed air or pressurized hydraulic oil can also be
used for power.
7. Flow Rate and Pressure
Your total volume and knowing how much time you have to move the fluid will determine
flow rate. Pump differential pressure can be calculated by knowing pipe size (length & fittings),
static lifts, and system equipment (filters, valves, etc.) friction losses.
4. Describe the working principle of radial piston pump with suitable sketch.
Piston pump has versatile applications due to robustness and highly efficient. Hydraulic
pumps, processing technology, drilling, etc. are a few of the applications which use piston
pumps. It is configurable for any kind of liquid and having a linear performance curve. Piston
pumps are used to move liquids or compressed gasses. It is categorized as one type of
hydraulic pump with robust and efficient performance. This article discusses an overview of the
piston pump and its working.
What is a Piston Pump?
Definition: It can be defined as a machine that is used to displace liquids or
compressed gases from one point to another. It is a positive displacement pump where a highpressure seal reciprocates with the piston. These pumps are used where there is a requirement
of high consistent pressure, like in water irrigation systems. Figure 1 shows the parts of the
piston pump in detail. The principle of working is explained in the following section.
Construction
As shown in the above figure, the piston pump consists of different parts. Each part is explained
in brief
 Intake- This is part of the pump where the input is given. It may be liquid or highpressure gas etc.
 Port Plate- This acts as the separating medium between the input port and output. The
compressed gas or liquid is sent out through this medium.
 Discharge- This forms the output of the pump
 Rotating Barrel: This is a dynamic part of the pump, in which the pistons are inserted in
their specific slots. When the barrel rotates, along with that the pistons rotate and
displace the liquid or compressed gas.
 Piston- This forms the most important part of the pump. They are the interfacing
medium between the nonrotating swash plate and the barrel. Pistons do have a springlike system such that they reshape their size when the barrel revolves.
 Nonrotating Swash Plate- This is the interface for the external system and pistons. The
pistons reshape themselves, get compressed when they come down under a force by
the swashplate. The swashplate is a non-rotating part. It is fixed to the shaft.
 Shaft- The shaft is coupled to the rotating barrel and the swashplate. On the shaft, the
complete assembly is housed.
Piston Pump Working Principle
The operating principle is explained in points below The figure shown is for axial flow variable displacement piston

The outlet port and inlet port are used intake and exhaust of the operating liquid or
gas. These are placed in a casing made up of iron.
The driveshaft is coupled to a swashplate and rotating barrel. The swashplate adjusts
itself based on the position of barrel and pistons. As shown in the figure, we have two colors for
the inlet and outlet port. When the barrel rotates, the piston which is placed upside, and pressed
inside and similarly the piston which is place downsides, is pressed outside. There is an
inclination in the position of the swashplate. The same position is reversed for the next cycle of
operation such that the location of piston completely forms a cycle. This helps in gas or liquids
to be displaced from one location to other i.e. from the input port to outlet port.
The pistons rotate along with the barrel in line with the position of the swashplate. The
pistons are placed inside a cylindrical block. The movement of the pistons causes a difference
in pressure, which causes suction of the inlet liquid or compressed gasses. The inclination in the
vertical position of the swashplate is up to 10 to 15 degrees. Because of this reason, it is called,
axial flow and variable displacement piston.
The motion of the piston is called reciprocating motion. The continuous motion i.e.
suction and discharge by the pistons cause the displacement in the liquid or compressed
gasses. When the angle decrease, we have less suction, and when the angle increase we have
more. For that reason, it is called a variable displacement piston. The variable displacement
depends on the swashplate angle.
Advantages and Disadvantages
The advantages of piston pumps are given as
 The working force in a piston pump can be controlled without moving the flow rate

The performance of the pump is not affected by the rate of flow and pressure of the
liquid or compressed gas
 In this pump, as compared to the vacuum pump, the range of pressure is wide.
The disadvantages of the piston pump are:
 Due to its assembly piston pump is heavy and bulky.
 They are capable of handling only lesser flower rates
 The flow is pulsating
UNIT II
1. What is the function of hydraulic motor and how does it differ from the hydraulic
pump?
While a hydraulic pump is connected to a prime mover, with the pump shaft with no extra
radial load, the hydraulic motor is connected to the load via pulleys, sprockets and gears, so its
main shaft can bear an increased radial load. A hydraulic pump typically has a vacuum in its low
pressure chamber.
2. Where are external gear motors used?
External gear pumps are commonly used for pumping water, light oils, chemical
additives, resins or solvents. They are preferred in applications where accurate dosing or high
pressure output is required. External gear pumps are capable of sustaining high pressures.
3. Why is end cushioning provided in hydraulic cylinder operations?
Cushioning is needed to lower the speed of the cylinder before it reaches the end cap.
Lowering the speed of the piston helps reduce stress on the components within the cylinder. It
also lessens vibration conveyed to the other parts of the machine.
4. Describe the function of check valves.
A check valve is a device that only allows the flow of fluids in one direction. ... Since they
only allow media flow in one direction, they are commonly referred to as 'one way valves' or 'non
return valves. The main purpose of a check valve is to prevent backflow in the system.
5. Draw the ANSI symbol for Pilot operated check valves and shuttle valves.
Check Valve
Shuttle valve
PART B
1. Explain with neat sketch about compound pressure relief valve
Compound Pressure Relief Valve
A pilot-operated pressure-relief valve consists of a small pilot relief valve and main relief
valve
as
shown
in
Fig.
1.4.
It
operates
in
a
two-stage
process:
1.The pilot relief valve opens when a preset maximum pressure is reached.
2. When the pilot relief valve opens, it makes the main relief valve open.
The pilot-operated pressure-relief valve has a pressure port that is connected to the
pump line and the tank port is connected to the tank. The pilot relief valve is a poppet type. The
main relief valve consists of a piston and a stem. The main relief piston has an orifice drilled
through it. The piston has equal areas exposed to pressure on top and bottom and is in a
balanced condition due to equal force acting on both the sides. It remains stationary in the
closed position. The piston has a light bias spring to ensure that it stays closed. When the
pressure is less than that of relief valve setting, the pump flow goes to the system. If the
pressure in the system becomes high enough, it moves the pilot poppet off its seat. A small
amount of flow begins to go through the pilot line back to the tank. Once flow begins through the
piston orifice and pilot line, a pressure drop is induced across the piston due to the restriction of
the piston orifice. This pressure drop then causes the piston and stem to lift off their seats and
the flow goes directly from the pressure port to the tank.
The advantages of pilot-operated pressure-relief valves over direct-acting pressure-relief
valves
are
as
follows:
1. Pilot-operated pressure-relief valves are usually smaller than direct-acting pressure-relief
valves
for
the
same
flow
and
pressure
settings.
2. They have a wider range for the maximum pressure settings than direct-acting pressure-relief
valves.
3. They can be operated using a remote while direct-acting pressure-relief valves cannot.
Graphic symbol of a pressure-relief valve is shown in Fig. 1.5. The symbol shows that the valve
is normally closed (the arrow is offline). On one side of the valve, pressure is fed in (the dashed
line) to try to open the valve, while on the other side, the spring tries to keep it adjustable,
allowing the adjustment of pressure level at which the relief valve opens. The arrow through the
spring signifies that it is adjustable, allowing the adjustment of pressure level at which the relief
valve opens.
2. Design the hydraulic drilling circuit using sequence valve and explain with neat
sketch.
In hydraulic circuits, sequence valve is used to perform two operations in sequence one
after the other. For example first cylinder-1 will extend and after that cylinder-2 will extend. It has
an adjusting screw, a spring and a conical poppet, which are, mounted inside the valve body as
shown in figure.
Example OF DRILLING MACHINE
The above figure shows the hydraulic circuit using two sequence valves to control two
operations performed in a proper sequence in both directions. The circuit uses manually
operated 4/2 DCV. In the example shown in the above figure, first the work piece should be held
firmly, and then drilling should be done. After this the drill bit should be removed from work piece
and then the work piece should be released by the vice. In first position of 4/2 DCV, oil flows to
cylinder C1, hence C1 extends, the movable jaw of the vice holds the work piece. By the
completion of extension of C1, pressure in the line increases hence the sequence valve V1
opens to allow oil to flow to cylinder C2. Hence C2 extends to move the drill bit down wards. In
second position of 4/2 DCV, oil flows to cylinder C2, hence C2 retract, the drill bit is removed
from the work piece. By the completion of retraction of C2, pressure in the line increases hence
the sequence valve V2 opens to allow oil to flow to cylinder C1. Hence C1 retracts to move the
movable jaw back wards to release the work piece.
3. Explain the working principle of different types of cylinders used in hydraulic
system.
A hydraulic cylinder is a key hydraulic component. It serves as a hydraulic consumer that
converts the energy of the hydraulic fluid into useful work. Its input value is the hydraulic fluid
under pressure acting on the surface of the hydraulic cylinder piston. This causes a linear
movement of the piston and thus the piston rod, which is connected to the load. Therefore, the
energy of the hydraulic fluid is transformed into a controllable power, which acts in a straight
line. The hydraulic medium is usually mineral oil, and in hydraulics, synthetic oils and emulsions,
as well as water (water hydraulics), are also used.
Hydraulic cylinder components
Hydraulic cylinders are composed of two main elements, namely the barrel and the
piston with an attached piston rod. The cylinder bottom and the cylinder head close both sides
of the barrel respectively. The piston rod exits through the cylinder head. The piston, equipped
with seals and sliding rings, divides the inside of the cylinder into two chambers, the lower
pressure chamber and the upper piston rod chamber. The hydraulic pressure is generated by
the piston that moves the piston rod in a linear direction. This type of cylinder is also called a
double–acting hydraulic cylinder.
SINGLE ACTING HYDRAULIC CYLINDERS.
The characteristic of the single–acting piston hydraulic cylinder is that the operating
stroke is only generated in a single direction; whereas, the return stroke is enabled by the load,
spring or any other exterior force. Typically the working stroke can be generated as cylinder
extraction, therefore this cylinder is a push cylinder; or the working stroke can be generated as
cylinder contraction. This type of cylinder is called a pull cylinder.
DOUBLE ACTING HYDRAULIC CYLINDERS
Hydraulic cylinders with double acting operation (double-acting hydraulic cylinders) have
two opposite facing piston surfaces that control the operation of the force of the hydraulic liquid,
i.e. usually a special hydraulic oil that enables two active moving directions. The hydraulic
energy is converted through the hydraulic liquid into the mechanical energy for the movement of
the pistons. The pistons usually have separate connections that enable active movement in both
directions. The force is thus applied in both directions and the structure of this hydraulic cylinder
is very simple.
This type of cylinder with linear movement is especially suitable for use in presses and
chippers, for opening and closing drawers and for all types of raising and lowering devices. The
piston rod is attached to the piston in this structure. The piston can move faster if it has a
smaller surface and slower if its surface is larger. This hydraulic cylinder is used for many types
of construction machinery.Hydraulic cylinders with double acting operation are divided
into differential and synchronous types.
TELESCOPIC CYLINDERS
Telescopic cylinders or multi–stage cylinders are composed of a number of cylinders
stacked on top of each other. Where the cylinder barrel also acts as a piston rod. Cylinders can
have two, three, four, five or even six stages. They are most often used where the cylinder
installation length is less than the required stroke. Most telescopic cylinders are single–acting,
but there are also double–acting telescopic cylinders available.
TANDEM CYLINDERS
Tandem cylinders are two interconnected cylinders. The piston rod of the first cylinder
enters through the base of the second cylinder and pushes its base. In this manner the greater
effective surface area of both pistons generates greater force, despite a small cylinder diameter
and unaltered operating pressure.
UNIT III
1. What is the function of pressure intensifier?
The hydraulic intensifier is a mechanical device which is used to increase the
intensity of pressure of the fluid. It utilizes the energy of large quantity of liquid at low
pressure.These machines require high pressure for this operation to obtain the required amount
of pressure.
2. List any four applications of accumulators.
 Construction. Energy storage capability & pulsation dampening to smooth out the bumps,
reduce the vibration, provide stability, safety and comfort. ...
 Oil and Gas
 Energy
 Fluid Power
 Agriculture
 Automotive Applications
 Suspension
3. What type of gases used in a gas loaded accumulator? Why oxygen not used
for this purpose?
Inert gas is used because oxygen and oil can form an explosive mixture when combined
under high pressure. As the volume of the compressed gas changes, the pressure of the gas
(and the pressure on the fluid) changes inversely.
4. What is the purpose of air over oil intensifier circuit?
Purchased or special built air-over-oil circuits provide smooth control when power
requirement is low. Some manufacturers make self-contained air-powered cylinders with built-in
oil cylinders and reservoirs. Air provides thrust while oil controls speed and/or mid stroke
stopping.
5. What is the purpose of using fail safe circuit in any hydraulic system?
Fail-safe circuits are those designed to prevent injury to the operator or damage to the
equipment. In general, they prevent the system from accidentally falling on an operator and also
prevent overloading of the system.
PART B
1. Design the accumulator circuit for the application of leakage compensator and
auxiliary power source in the hydraulic circuit.
A hydraulic accumulator is a device that stores the potential energy of an incompressible
fluid held under pressure by an external source against some dynamic force. This dynamic force
can come from different sources. The stored potential energy in the accumulator is a quick
secondary source of fluid power capable of doing useful work. It is a simple hydraulic device
which stores energy in the form of fluid pressure. This stored pressure may be suddenly or
intermittently released as per the requirement.
In the case of a hydraulic lift or hydraulic crane, a large amount of energy is required
when the lift or crane is moving upward. This energy is supplied from the hydraulic accumulator.
But when the lift is moving in the downward direction, it does not require a huge amount of
energy. During this particular time, the oil or hydraulic fluid pumped from the pump is stored in
the accumulator for future use.
Accumulator can be used as a compensator for internal and external leakage during an
extended period during which the system is pressurized but not in operation. The pump charges
the accumulator and the system until the maximum pressure setting on the pressure switch. The
contacts on the pressure switch then open to automatically stop the electric motor that derives
the pump. The accumulator then supplies leakage oil to the system during a long period. Finally,
when system pressure drops to the minimum pressure setting of the pressure switch, it closes
the electrical circuit of the motor until the system has been recharged.
The check valve is placed between the pump and accumulator so that the pump will not
reverse when the motor is stopped and will not permit all the accumulator charge to drain back
into the power unit. With this circuit the only time the power unit operates is when the pressure
drops to a unsafe operating level. This saves electric power and reduces the heat in the system.
2. Design the accumulator circuit for the application of hydraulic shock absorber
and Emergency power source in the hydraulic circuit.
Accumulator as a hydraulic shock absorber
One of the important applications of accumulator is the elimination of hydraulic shock.
Hydraulic shock is caused by the sudden stoppage or declaration of a hydraulic fluid flowing at
relatively high velocity in a pipe line. By rapidly closing a valve creates a compression wave.
This compression wave travels at the speed of sound upstream to the end of the pipe and back
again to the closed valve, which causes an increase in pressure. The resulting rapid pressure
pulsations or high pressure surges may cause damage to the hydraulic system components. If
an accumulation is installed near the rapidly closing valve, the pressure pulsations or high
pressure surges are suppressed.
Accumulator as an auxiliary power source
The purpose of accumulator in this application is to store the oil delivered by the pump
during a portion of the work cycle. The accumulator then releases the stored oil on demand to
complete the cycle, there by serving as a secondary power source.
When the four way valve is manually activated oil flows from the accumulator to blank
end of cylinder. This extends the piston until it reaches the end of the stroke. When the cylinder
is in its fully extended position, the accumulator is being charged. The four way valve is then
deactivated for retraction of the cylinder oil flows from both pump and accumulator to retract the
cylinder rapidly.
3. Design and explain the working of a sequencing circuit
The circuit depicted in Figure 10.6 contains a hydraulic system in which two sequence
valves are used to control the sequence of operation of two double-acting cylinders.
When the DCV is shifted into its left envelope mode, the left cylinder extends completely
and then the right cylinder extends. If the DCV is shifted into its right envelope mode, the right
cylinder retracts fully followed by the left cylinder. This sequence of the cylinder operation is
controlled by the sequence valves. The spring centered position of the DCV locks both the
cylinders in place.
The best example of this circuit is the case of a production operation. The left cylinder
should extend in order to accomplish the job of clamping a work piece with the help of a power
vice jaw. The right cylinder extends to drive a spindle to drill a hole in the work piece. After the
hole has been drilled, the right cylinder retracts first and then the left one. The sequence valve
installed in the circuit ensures that these operations occur in a predefined fashion.
UNIT IV
1. List the purpose of an Air lubricant.
Air lubricators have been an important part of pneumatic systems for decades.
Lubrication helps reduce friction between sliding surfaces to not only improve efficiency and
increase cycling speed of a component, but reduces wear, which ultimately means longer
component life and less maintenance.
2. Discuss the function of an air filter
It's basic function is to clean the air that circulates through your heating and cooling
system. Filters trap and hold many types of particulates and contaminants that could affect your
health and comfort, including: Dust and dirt. Pollen.
3. Discuss the need of lubricator unit in the pneumatic system.
A pneumatic lubricator injects an aerosolized stream of oil into an air line to provide
lubrication to the internal working parts of pneumatic tools, and to other devices such as
actuating cylinders, valves, and motors. A lubricator should always be the last element in an
FRL (Filter-Regulator-Lubricator) unit.
4. Define fluidics
Fluidics, the technology of using the flow characteristics of liquid or gas to operate
a control system. One of the newest of the control technologies, fluidics has in recent years
come to compete with mechanical and electrical systems.
5. Define Programmable Logic Control (PLC).
A programmable
logic
controller (PLC)
or programmable
controller is
an
industrial computer that has been ruggedized and adapted for the control of manufacturing
processes, such as assembly lines, machines, robotic devices, or any activity that requires high
reliability, ease of programming, and process fault diagnosis.
PART B
1. Define compressor. Explain the working principle of piston type compressor and
screw type compressor with neat sketch.
A mechanically operated machine that rises the fluid pressure by reducing its volume is
called a Compressor. If the compressor uses gas as a working fluid, it is called a gas
compressor. While if the air uses as a working fluid, it is called an air compressor. Naturally, in a
compressor, the compressed air gas rises the temperature.
An air compressor is also a specific kind of machine that operates with compressed air
aid and is used in different industries. The air compressor has gained worldwide recognition
after its discovery in the year 1875.
With the help of the air compressors, people could save their time and money in almost
every work. It was even found that these devices had a great impact on the lives of the people.
A lot of work was taken up by the people who were able to reduce their work, and this has led to
a major increase in the productivity of the people and their performance levels. This is the main
reason why the demand for compressors has gone up drastically.
Reciprocating Compressors
These types of air compressors use a piston or plunger that pushes by a crankshaft.
This piston or plunger moves at a constant speed to pull the air in then compresses it. Typically,
one drive of the piston sucks the air in the cylinder, and the other drive squeezes it.
The small reciprocating compressors have power from 5 to 30 horsepower that is mostly
found in the applications of automobiles and are generally used for intermittent operation.
Large reciprocating compressors are more than 1000 horsepower and are commonly
used in petroleum and large industrial applications. In large industries, these are used for
applications like chemical plants, industry, oil refineries, and natural gas processing and
delivery.
Advantage of Reciprocating Compressors:
 These are easy to maintain
 These are best for applications that need high pressure
 Very highly efficient and flexible
 It has a simple design
Disadvantages of Reciprocating Compressors:
 These compressors produce high noise
 It is a highly vibrating equipment
 It has a large size
Rotary Screw Compressors
These are the most common types of air compressors used nowadays. In a rotary screw
compressor, air sucks into the compressor, closes the openings, and compresses the air with
the help of two rotors that rotate continuously and run via the cavity. With each revolution, the
air pressure gradually increases until it touches the desired pressure.
The classification of the screw compressors depends on the type of gearbox, the method
of cooling, and the stage. These types of air compressors generally manufacture in dry variety,
water and oil flooded.
The rotary compressor′s efficiency is very dependent on the air dryer. Screw
compressors have few components, high efficiency, large capacity, simple structure, voltage
spikes, and low vibration and can run at low speed to adjust power.
Advantages:
 These don‘t use a piston
 These have higher than piston compressors
 This compressor gets less space for installation
 It has less vibration and types than other types
 It has high reliability
 Highly efficient
 It has a long service life
Disadvantages:
 These have a high cost than other positive displacement compressors
 These also need high maintenance
 High precision
 It needs for special equipment processing
 High service cost
2. Design and draw a circuit using the hydraulic components for the Shaping operation
Shaping machine uses a single-point cutting tool. This tool makes a reciprocating
motion on the workpiece. In half reciprocating stroke the tool cuts the metal and in the second
half, the tool returns to the original positions. Shaping machine is not a production machine. It is
widely used in tool rooms of machine shops.
To generate reciprocating motion of ram of shaping machine we having two alternatives:
1. By using a four-bar mechanism ( Cylinder, Piston, connecting rod, and crank ) driven by the
motor. This machine is called a mechanical shaping machine.
2. By using a hydraulic DA cylinder. This machine is called a hydraulic shaping machine.
A typical hydraulic drive for horizontal shaper is shown in Fig. A constant speed motor drives a
hydraulic pump which delivers oil at a constant pressure to the line. A regulating valve admits oil
under pressure to each end on the piston alternately, at the same time allowing oil from the
opposite end of the piston to return to the reservoir.
Working Of Hydraulic operated Shaper machine :
The piston is pushed by the oil and, being connected to the ram carrying the tool. The
admission of oil to each end of the piston, alternately, is accomplished with the help of trip dogs
and pilot valve. As the ram moves and completes its stroke (forward or return) a trip dog will trip
the pilot valve which operates the regulating valve. The regulating valve will admit the oil to the
other side of the piston and the motion of the ram will get reversed. It is clear that the length of
the ram stroke will depend upon the position of the t by unclamping and moving the trip dogs to
the desired positions.
The above system is a constant pressure system. The velocity of the ram travel will be directly
proportional to the oil pressure and since the piston area on which the oil pressure acts is
greater as compared to the other end for which it gets reduced because of the piston rod. the
hydraulic power to mechanical power for feeding the work past the tool.
Advantages of Hydraulic Shaping machine
1. Does not make any noise and operates very quietly
2. Ability to stall against an obstruction without damage to the tool or the
3. Ability to change length and position of stroke or speed while the machine is running
4. The cutting and return speeds are practically constant throughout the stroke. This permits
the cutting tool to work uniformly during the cutting stroke.
5. The reversal of the ram is obtained quickly without any shock as the oil on the other end of
the cylinder provides a cushioning effect.
6. Offers great flexibility of speed and feed
7. Relief Valve ensures proper pressure supply hence machine overloading is avoided.
8. More strokes per minute can be achieved by consuming less time for reversal and return
stroke.
Disadvantages of Hydraulic Shaping Machine:
 Hydraulic shaper machine is more costlier than mechanical shaper
 The stopping point of the cutting stroke in a hydraulic shaper can vary depending upon the
assistance offered to cutting by the work material.
 Leakage of oil poses a major problem in machine tools. When the amount of leakage
increases the capacity of the unit reduces and the efficiency goes down.
Application Hydraulic Shaper machine :
 To generate straight and flat surfaces
 To smooth rough surfaces
 To make internal splines
 To make gear teeth
 To make dovetail slides
 To make keyways in pullies or gears
3. Explain in detail about how the failure and trouble shooting is carried out in pneumatic
system
The word troubleshooting in the minds of production managers, plant managers, and
maintenance personnel means hours of lost production and downtime. But when it comes to
troubleshooting pneumatic valves or systems, it‘s a necessary step by step procedure that
corrects the functions of systems to regain the proper operations of devices.
Here are some of the steps of troubleshooting such systems:
Observe Safety. One of the crucial parts of troubleshooting is safety. A maintenance personnel
should always regard this, first and foremost, as compressed air is an unstable element in a
pneumatic circuit. Many have been injured due to explosions from air receiver tanks. It can
cause severe injuries to maintenance personnel and can even damage properties. When
troubleshooting, you need to be more cautious as the air is also highly compressible.
Moreover, don‘t forget to wear protective gear before inspecting any equipment.
Conduct Inspection. Walking around the machine or a visual inspection can help identify
problems such as loose and broken components and worn or burst hoses. This is to make sure
that you are familiar with the components in the pneumatic system. It is vital to ask as many
pertinent questions as possible if you are not familiar with the components or machine
operations.
Before trying to troubleshoot, you need to consider understanding the interrelations of all
the components.
Read the Schematics. Read and understand the schematics when trying to repair systems.
They contain useful information about the pneumatic system such as pressure test point
locations, flow rates within the system, air motor speeds, and other essential functions. They
can help in identifying if the system is operating within its parameters.
A schematic is a roadmap that explains not only the operation function of the components but
also serves a useful diagnostic tool.
Operating the machine. After familiarising with the operation and system components, you can
start operating the machine to get a first-hand view of any issues. Don‘t forget to check if any
malfunction in the machine occurs again, as visual inspection is vital when operating the
machine.
Common issues regarding the machine include excessive air leakage, unidentified
pressure levels, loose manual operations, and erratic functioning components.
Troubleshooting pneumatic valves or systems can be difficult if you don‘t know the proper
procedures. With these steps, you will be able to identify and understand the certain steps that
you can apply to any troubleshooting problem.
4. List down the features of low cost automation
Every manufacturing industry, irrespective of size and budget, can automate its
assembly lines by incorporating a new approach towards infrastructure efficiency, resultoriented employees empowered to work across various technical disciplines and a flexible
hands-on project management style. Low-cost automation (LCA) strategy completely relies on
the in-house resources that can concurrently grow with the project, and ultimately get integrated
into the company infrastructure upon completion of the project.
Benefits of LCA:
1. As the name itself implies, the investment cost is low, and ROI is high in terms of improved
productivity and better work efficiency.
2. It provides quality, flexibility, increases productivity, reduces cost, and can be easily
implemented and affordable by SMEs.
Application of LCA:
Commonly, LCA is used in manufacturing processes like grinding, material handling, machining,
cold-extrusion, quality inspection, dimensional accuracy, surface finishing and assembly, and
packaging.
The approach towards Low-cost automation involves the following steps:
1. Scope of the project: This step involves determining the processes to be automated, the
sequence of operations, minimum level of automation and control for every process, minimum
level of material handling between every process, and the target throughput rate. It emphasizes
identifying the minimum criteria for the overall system. To maintain low cost, the content of the
project must be consistently guided by essentials only.
2. Building infrastructure to support the project: Create areas for fabricating and assembling
parts, subsystems, and entire machines. This includes a machine shop, stock room for
consumables, fasteners, controls fabrication area, pneumatic components, and electric panel
supplies. This costs relatively lesser than the typical manufacturing automation project.
3. Building the system: The A team should consist of engineers experienced in designing
electrical, mechanical, and software systems. They should even be ready to install pneumatic
components, handle dirty fabricating parts in a machine shop, or wiring a control panel before
programming the PLC. The team should handle and resolve even the post-production issues.
The idea is to keep the workflow on the system all the time, with seamless transitions from one
engineering discipline or technical trade to another, while resolving the problems.
Maintenance Benefits:
1. One of the most visible benefits of LCA is the development of an expert equipment
maintenance infrastructure. The entire responsibility of maintenance lies in the hands of the
engineers who designed and fabricated the system.
2. It also helps to ensure the maintenance, repair, and up-gradation of the system regularly, thus
increasing the lifespan and reducing the downtime.
3. Extraordinary Labor efficiency saves time and money.
4. Reduced expenses for sample parts in bulk, as they can be acquired only when required.
Labor Efficiency:
One major benefit of LCA includes the overall expertise of engineers who efficiently handle the
project from start to end, reducing the cost of hiring other supervisory and technical staff. In this
lean organization, everyone becomes a key contributor and decision-maker. The collective
talents of engineers are simultaneously utilized for documentation, new technology
investigations, technical writing, process development, calibration, skill development,
instrumentation, etc. This is a challenge for engineers to broaden their skills. The ability to
accommodate design changes is helpful, especially when novel processes are automated for
the first time. All the brainstorming results in design convergence, yielding refined ideas from the
beginning of the project.
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UNIT V
1. List any two selection criteria of pneumatic systems
Flow vs. pressure
Use electric actuators
Valve sizing
Align pipelines
Choose 3-position valves
Check temperatures
Built-in flow control
2. How a hydraulic system breaks down?
Air and water contamination are the leading causes of hydraulic failure, accounting for
80 to 90% of hydraulic failures. Faulty pumps, system breaches or temperature issues often
cause both types of contamination.
3. Name any two faults that can be found in pneumatic systems.
Because some pneumatic machines are more complex than others, there are several
issues that might arise with your pneumatic systems, including:
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Actuator moving too slowly.
Pressure too low.
Too much air choke.
Air seal leaks.
Dirty or damaged filter.
Directional control valve not changing direction.
Cylinder drift.
4. Conclude that, how does microprocessors use in hydraulic and pneumatic
systems.
A microprocessor based control system has been developed and used to provide
satisfactory control of a pneumatic servo system. This paper describes how microprocessor
based controls can be used to produce low cost pneumatic servo drives which could find a wide
range of application in manufacturing industries. The pneumatic actuator is a piston air motor
constructed of aluminium, utilising a proportional spool valve to allow air flow control.
5. List four types of faults and causes of hydraulic system break down.
We can trace most hydraulic issues back to a few common causes, listed below.
1. Air and Water Contamination. Air and water contamination are the leading causes of hydraulic
failure, accounting for 80 to 90% of hydraulic failures.
2. Temperature Problems.
3. Fluid Levels and Quality.
4. Human Error.
PART B
1. Design the hydraulic drilling circuit using sequence valve and explain with a neat sketch
The circuit depicted in Figure 10.6 contains a hydraulic system in which two sequence
valves are used to control the sequence of operation of two double-acting cylinders.
When the DCV is shifted into its left envelope mode, the left cylinder extends completely
and then the right cylinder extends. If the DCV is shifted into its right envelope mode, the right
cylinder retracts fully followed by the left cylinder. This sequence of the cylinder operation is
controlled by the sequence valves. The spring centered position of the DCV locks both the
cylinders in place.
The best example of this circuit is the case of a production operation. The left cylinder
should extend in order to accomplish the job of clamping a work piece with the help of a power
vice jaw. The right cylinder extends to drive a spindle to drill a hole in the work piece. After the
hole has been drilled, the right cylinder retracts first and then the left one. The sequence valve
installed in the circuit ensures that these operations occur in a predefined fashion.
2. Narrate a case study of low cost automation
Robotic Arm: This case study is from ―KEDAR PRECISION COMPONENT‖, this industry is
specialized in double grinding process. Currently they are facing a problem in terms of safety of
labors, human fatigue problems and expenditure related to labors. When components are fed
for grinding in duplex machine there is chance of injury to the operator. Also for such simple job
minimum pay for labor are not affordable. Hence to overcome this pick and place job a robotic
arm is used. We are currently working on this project with the industry. Now day‘s industry is
very widely using robots and automation solution for repeating and unskilled works. As less
precise work requires less investment for providing automation many low cost robotic arms are
available in market. Robotics industry is growing very fast and still has a lot of work and
research to be done yet. ―Industry 4.0‖ is the upcoming era of industry. After surveying for
automation solution and needs we found that Robots are the future in many jobs, but pick and
place type less accurate jobs are going to be done with help of robotic arm. So, to develop the
best solution at least cost is the main theme in developing ―Autonomous robotic arm‖.
A. Need and Concept : Robotic arm available in market are very much costlier in our region
due to many facts like Import duty on Robot, on its parts, Les competition, relatively less
knowledge to reduce cost, etc. After visiting some of double grinding machine industries we
have found a particular problem of feed jobs into duplex machine as the grinding wheels are
running above 3000 rpm it is unsafe to feed the job manually also it requires a person to
continuously pick the raw material and place on machines magazine which makes it less
productive process. So in order to overcome this difficulty a pick and place robotic arm must be
used which will perform both the operation of picking the raw material and feeding it to duplex
machine. Also in many industries for arranging the component in particular order one labor is
required which is hectic job and also there are chances of Human fatigue error. In foundry
industry for lifting and pouring the molten metals cranes are used but in small scale foundries or
in such cases where less quantity is required to pour or when for making correct composition
other materials are required to melt, in such cases use of crane is not economical also very
difficult if the mold is small. So, Robotic arm can perform such functions economically and also
with ease. In hotel industry for lifting the heavy cans, hot and heavy utilities robotic arm can be
used also with providing some attachment can make it possible to serve the dishes to the
consumers these are some needs explained by some owners and experts in this industry.
B. Manufacturing process : There are many ways of manufacturing parts of a robotic arm.
But the dimensions of robotic arm many times changes according to the application and its
working environment, availability of space. Hence it become more costly if one adapts
conventional processes for manufacturing parts of robotic arm. Also the weight of Arm will make
systems bulky if conventionally manufactured. Use of advanced manufacturing processes in
developing and manufacturing robotic arm will be beneficial in terms of cost as well as time.
There are several techniques which are developed to manufacture single or less quantity of
component at less cost. Some examples of techniques for such small batch production or
testing components are improving old machine tools with attachments, use of Additive
Manufacturing (AM) methods, etc. Major advantages of using AM techniques are reduction in
lead time of manufacturing, reduction in overall cost of manufacturing by prototyping and
concept testing. Higher flexibility in manufacturing leads to easier imagination and hence new
type of design can be developed. Design failures can be identified in early stage which is
preventing major losses in terms of investments, reliability and customer satisfaction.
C. Assembly : While assembling robotic arm with controller and Bluetooth module it will much
helpful if the pins and ports are already decided. As they can be directly used while
programming as input and output ports and programming can be done easily. Also some circuits
for power supply are required also use of power source such as SMPS are also recommended
as smooth and continuous supply of current is obtained. Also it is better to know how to
assemble the shafts with links which are manufactured and how to mount motors and their
connections.
D. Circuit : As there are total 6 number of servo motors and 3 ultrasonic sensor or 2 ultrasonic
and 1 proximity sensor and Bluetooth module it is necessary to give power supply from external
circuit rather than using arduino supply directly. As arduino is an open source and there are
variety of circuits available in market which are known as arduino shields can be directly used
and mounted on it and much simple and neat type of system can be build. Schematic circuit for
5 servo and 3 ultrasonic sensors along with Arduino mega is shown in Figure 1.
E. Algorithms and libraries: Programming is main thing which is going to control all the
operations and making the robot autonomous. As machine learning is going to be much helpful
for doing robot self-learning and hence improving same for the decision making. Arduino IDE is
our platform for coding along with following libraries: Servo, Wi-Fi/Bluetooth, Serial.
Step 1: Check for obstacles.
Step 2: Move the motor at base to desired angle
Step 3: Move the motor at above base to desired angle
Step 4: Move the motor 4 to desired angle
Step 5: Move the motor 3 to desired angle
Step 6: Move the motor 2 to desired angle
Step 7: Check for material, if material sensed, Move the motor 1 to desired angle, else move the
motor at base until material is sensed, then move motor 1 to desired angle.
Step 8: Move the motor 2 to desired angle
Step 9: Move the motor 3 to desired angle
Step 10: Move the motor 4 to desired angle
Step 11: Move the motor 5 to desired angle
Step 12: Check for obstacles and with sensing for obstacles move the motor 6 to desired angle
Step 13: Move the motor 5 to desired angle
Step 14: Move the motor 4 to desired angle
Step 15: Move the motor 3 to desired angle
Step 16: Move the motor 2 to desired angle
Step 17: Move the motor 1 to desired angle
Step 18: Move the motor 2 to desired angle
Step 19: Move the motor 3 to desired angle
Step 20: Move the motor 4 to desired angle
Step 21: Move the motor 5 to desired angle
Step22: Check for obstacles and with sensing for obstacles move the motor 6 to desired angle
With this algorithms for variety of jobs robotic arm can be programmed.
When work is required to be set on priorities that time using Assignment problem of
operational research for decision of job or work selection is done.
F. Design and Calculation : Design part consists of choosing material and finalizing the
dimension of links and also calculation of torque of motor. G. Material selection: After deciding
to manufacture Robotic arm by using 3D printing we studied 3 materials PLA, ABS and Carbon
Fiber Composite. As Carbon Fiber has very good strength it is an ideal material which can be
used for manufacturing of links but it is also very expensive almost 2.5 times of PLA. ABS is
good but due to its tendency of warping after cooling we decided not to select ABS. PLA has
good strength of 46.76MPa in tension and also half in shear also its very much cheaper than
Carbon fiber composite. So we decided to Select PLA.
4. Explain the ladder logic diagram with a suitable example
Latching in a PLC
Latching is one of the most important pieces of ladder logic programming that you‘ll ever use.
When we use the term latching in a PLC it refers to changing the state of an output to TRUE,
holding the state of that output TRUE until certain conditions occur, then returning the state of
the output back to FASLE.
This can be achieved with two methods….
1. Set and Reset instructions. In an Allen Bradley PLC they are called Latch and
Unlatch instructions. These instructions simulate the function of an electromechanical
latching relay. Advantages include flexibility in programming because the Set (Latch)
and Reset (Unlatch) symbols do not need to be in the same rung. The disadvantage is
that debugging can become more difficult because the Set (Latch) and Reset (Unlatch)
symbols may be scattered throughout the program.
2. Latching logic. Quite often hold in logic is referred to as hold in logic. It‘s ok to
interchange the terms. The advantage of latching logic is that troubleshooting is easier
because the symbols used are all in the same rung. The disadvantage is that there is
some inflexibility in programming because latching logic requires all the symbols to be
on the same rung and may even overflow to the next rung. This can be restrictive in
some cases.
Simple applications requiring a latch are well suited to use latching logic.
But when it comes to more complex applications the use of Set (Latch) and Reset (Unlatch)
symbols may be required.
Sometimes it just comes to personal preference.
Latching in a PLC requires at least one input to set the latch (Input A), one input to reset the
latch (Input B) and one output to store the latch state (Output Y).
The inputs that set and reset the latch are usually momentary pulses. A great example of a
device that can provide a momentary pulse to a PLC input is a push button.
PLC Motor Control
Ladder logic for motor control can be accomplished using hold in logic. Remember it‘s ok
to also call it latching logic.Simple ladder logic for motor control using push button start stop
logic includes a start button, stop button, motor thermal overload and motor run contactor. When
we wire up the inputs to the PLC the start push button input is wired normally open (NO). So
when the start button is pushed the PLC input changes state from FALSE to TRUE.
Wiring the stop push button normally closed (NC) is done because when a failure occurs
in the PLC input circuit it will, more often than not, lead to an open circuit which changes the
state of the PLC input from TRUE to FALSE.
However, if we wire the stop PLC inputs as normally open (NO) and a failure occurs then
the state of the PLC input does not change. It stays FALSE, even if the stop button is pressed,
because there is an open circuit in the connection to the PLC input.
So if there is no change in state, we cannot tell the motor to stop in our ladder logic
program. This is really bad!!!
So for any PLC input that is intended to stop the motor we need to..…
WIRE THE MOTOR STOP SIGNALS NORMALLY CLOSED AND USE A NORMALLY
OPEN SYMBOLS IN THE PLC.
Now that we‘ve grasped the concept of the fail safe stop input let‘s move on to the motor
control ladder logic programming example.
Motor Control Ladder Diagram
First up let‘s list the required inputs and outputs for our motor control ladder diagram.
PLC manufacturers use different memory address allocation so the input output allocations
used here are arbitrary address.
Below is the list of required inputs …..
Next let‘s list the required outputs…..
The ladder logic programming example uses the M1 START push button input to activate the
M1 RUN output.
The M1 RUN output is used a second time to latch the M1 RUN output.
Both M1 STOP and M1 TOL are wired normally closed (NC) to the PLC inputs and thus need to
be configured as normally open (NO) symbols in the logic.
So when either stop is activated the logic flow is broken and the latch is reset….
Ladder
Logic Programming Examples – Motor Control Ladder Diagram
Remember, we must wire M1 Stop and M1 TOL using normally closed (NC) contacts to the PLC
inputs to make it ―fail safe‖ and for this motor control ladder diagram to work.
5. Draw and explain the Air-over-oil circuit used in the hydraulic circuit
6. Explain with neat sketch about different types of flow control valve used in the hydraulic
systems.
The purpose of flow control in a hydraulic system is to regulate speed. All the devices
discussed here control the speed of an actuator by regulating the flow rate. Flow rate also
determines rate of energy transfer at any given pressure. The two are related in that the
actuator force multiplied by the distance through which it moves (stroke) equals the work done
on the load. The energy transferred must also equal the work done. Actuator speed determines
the rate of energy transfer (i.e., horsepower), and speed is thus a function of flow rate.
Directional control, on the other hand, does not deal primarily with energy control, but
rather with directing the energy transfer system to the proper place in the system at the proper
time. Directional control valves can be thought of as fluid switches that make the desired
"contacts." That is, they direct the high-energy input stream to the actuator inlet and provide a
return path for the lower-energy oil.
It is of little consequence to control the energy transfer of the system through pressure
and flow controls if the flow stream does not arrive at the right place at the right time. Thus, a
secondary function of directional control devices might be defined as the timing of cycle events.
Because fluid flow often can be throttled in directional-control valves, some measure of flow rate
or pressure control can also be achieved with them.
Different types of flow measurement
Controlling flow of a fluid-power system does not necessarily mean regulating volume
per unit of time from a valve. Flow rate can be specified three different ways, so it is important to
be aware of how flow is to be specified or measured:
Volumetric flow rate, Qv, expressed in units of in.3/sec or min - or cc/sec or cc/min in SI metric
measure - is used to calculate the linear speeds of piston rods or rotational speeds of motor
shafts.
Weight flow rate, Qw, expressed in units of lb/sec or lb/min, is used to calculate power using
English units of measure.
Mass flow rate, Qg, expressed in units of slugs/sec or slugs/min for English measure - or
kg/sec or kg/min in SI metric measure - is used to calculate inertia forces during periods of
acceleration and deceleration.
Because they control the quantity of fluid that flows through the valve per unit of time, the same
control valves are used for all three types of flow rates.
Control of flow rate with valves
Eight types of flow-control valves are used most often in hydraulic circuits:
Orifices — A simple orifice in the line, Figure 1(a), is the most elementary method for
controlling flow. (Note that this is also a basic pressure control device.) When used to control
flow, the orifice is placed in series with the pump. An orifice can be a drilled hole in a fitting, in
which case it is fixed; or it may be a calibrated needle valve, in which case it functions as a
variable orifice, Figure 1(b). Both types are non-compensated flow-control devices.
Flow regulators — This device, Figure 2, which is slightly more sophisticated than a fixed
orifice, consists of an orifice that senses flow rate as a pressure drop across the orifice; a
compensating piston adjusts to variations in inlet and outlet pressures. This compensating
ability provides closer control of flow rate under varying pressure conditions. Control accuracy
may be 5%, possibly less with specially calibrated valves that operate around a given flow-rate
point.
Bypass flow regulators — In this flow regulator, flow in excess of set flow rate returns to tank
through a bypass port, Figure 3. Flow rate is controlled by throttling fluid across a variable orifice
regulated by the compensator piston. The bypass flow regulator is more efficient than a
standard flow regulator.
Demand-compensated flow controls — Flow controls can also bypass excess system flow to
a secondary circuit, Figure 4. Fluid is routed at a controlled flow rate to the primary circuit, and
bypass fluid can be used for work functions in secondary circuits without affecting the primary
one. There must be flow to the primary circuit for this type of valve to function - if the primary
circuit is blocked, the valve will cut off flow to the secondary circuit.
Pressure-compensated, variable flow valves — This flow control is equipped with an
adjustable variable orifice placed in series with a compensator. The compensator automatically
adjusts to varying inlet and load pressures, maintaining an essentially constant flow rate under
these operating conditions to accuracy of 3% to 5%, Figure 5. Pressure-compensated, variable
flow-control valves are available with integral reverse-flow check valves (which allow fluid to flow
unrestricted in the opposite direction) and integral overload relief valves (which route fluid to
tank when a maximum pressure is exceeded).
Pressure- and temperature-compensated, variable flow valves — Because the viscosity of
hydraulic oil varies with temperature (as do the clearances between a valve's moving parts),
output of a flow-control valve may tend to drift with temperature changes. To offset the effects of
such temperature variations, temperature compensators adjust the control orifice openings to
correct the effects of viscosity changes caused by temperature fluctuations of the fluid, Figure 6.
This is done in combination with adjustments the control orifice for pressure changes as well.