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Unit-I HYDRAULIC SYSTEMS AND CONTROL COMPONENTS
MT2351 FLUID POWER SYSTEMS
Prepared by:
Dr. P. Balasundar, M.E., Ph.D.,
Assistant Professor (Senior Scale),
Department of Mechatronics Engineering,
KAMARAJ College of Engineering and Technology.

HYDRAULIC SYSTEMS AND CONTROL
COMPONENTS
Basic Components of Hydraulic power pack: Direction control,
Flow control and Pressure control valves-Types and working.
Hydraulic Actuators: Cylinders– Types and construction,
Hydraulic cushioning - Hydraulic motors. ANSI Symbols.
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Hydraulic power pack
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Hydraulic power pack
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A hydraulic power pack, also known
as a hydraulic power unit (HPU) or hydraulic
power station, is a self-contained system that
generates and delivers hydraulic power to
various hydraulic machinery and equipment.
The basic components of a hydraulic power
pack typically include:
? Hydraulic Pump
? Electric Motor
? Reservoir (Hydraulic Tank)
? Hydraulic Fluid
? Hydraulic Valves
? Accumulator
? Filtration System
? Cooling System
? Pressure Relief Valve
? Manifold or Control Block

1. Hydraulic Pump: The pump is responsible for generating the hydraulic pressure by converting mechanical energy
into hydraulic energy. There are various types of hydraulic pumps, such as gear pumps, vane pumps, and piston
pumps.
2. Electric Motor or Engine: The power pack is driven by an electric motor or an internal combustion engine, providing
the mechanical energy needed to drive the hydraulic pump.
3. Reservoir (Hydraulic Tank): The reservoir stores hydraulic fluid (usually hydraulic oil) and serves as a cooling and
filtering system for the hydraulic fluid. It also provides a space for air separation and allows for expansion and
contraction of the hydraulic fluid.
4. Hydraulic Fluid: The hydraulic fluid serves as the medium for power transmission in the hydraulic system. It should
have suitable viscosity, temperature stability, and lubricating properties to ensure proper system functioning.
5. Hydraulic Valves: These valves control the direction, pressure, and flow of the hydraulic fluid. Common types of
valves include directional control valves, pressure control valves, and flow control valves.
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6. Accumulator: An accumulator is a storage device that stores hydraulic energy in the form of pressurized fluid. It
helps smooth out pressure fluctuations, store energy for peak demands, and act as a backup power source in
case of a power failure.
7. Filtration System: The filtration system is essential for removing contaminants and particles from the hydraulic
fluid, ensuring the longevity and proper functioning of the hydraulic components.
8. Cooling System: Some hydraulic power packs incorporate a cooling system, such as a heat exchanger or a fan, to
dissipate heat generated during the operation of the hydraulic system. This helps maintain the optimal operating
temperature of the hydraulic fluid.
9. Pressure Relief Valve: The pressure relief valve is a safety device that limits the maximum pressure in the
hydraulic system, protecting the system from overpressure situations.
10. Manifold or Control Block: The manifold or control block is a component that houses various hydraulic valves
and connects them to the hydraulic circuit. It helps streamline the hydraulic system and facilitates easier
maintenance.
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Types of Control Valves
? Directional control valves
? Controls path of the fluid
? Flow control valves.
? Control the Flow rate in
fluid power.
? Pressure control valves
? Controls the system against
over pressure
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Direction Control Valves (DCV)
? A valve is a device that receives
an external signal (mechanical,
fluid pilot signal, electrical or
electronics) to release, stop or
redirect the fluid that flows
through it.
? The function of a DCV is to
control the direction of fluid flow
in any hydraulic system.
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Classifications of DCV
? Rotary spool type
? Sliding spool type
? Check Valve
? Ball type check valve
? Poppet check valve
? Pilot-Operated check Valve
? Shuttle valve
? 2/2 DCV
? 3/2 DCV
? 4/2 DCV
? 5/2 DCV
? 5/3 DCV
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? Rotary spool type
? Check Valve
? Shuttle valve
? 2/2 DCV
? 3/2 DCV
? 4/2 DCV
? 5/2 DCV
? 5/3 DCV
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? Rotary spool type
? Check Valve
? Shuttle valve
? 2/2 DCV
? 3/2 DCV
? 4/2 DCV
? 5/2 DCV
? 5/3 DCV
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? Rotary spool type
? Check Valve
? Shuttle valve
? 2/2 DCV
? 3/2 DCV
? 4/2 DCV
? 5/2 DCV
? 5/3 DCV
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? Rotary spool type
? Check Valve
? Shuttle valve
? 2/2 DCV
? 3/2 DCV
? 4/2 DCV
? 5/2 DCV
? 5/3 DCV
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? Rotary spool type
? Check Valve
? Shuttle valve
? 2/2 DCV
? 3/2 DCV
? 4/2 DCV
? 5/2 DCV
? 5/3 DCV
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A poppet is a specially shaped plug element held on a valve
seat by a light spring.

? Rotary spool type
? Check Valve
? Shuttle valve
? 2/2 DCV
? 3/2 DCV
? 4/2 DCV
? 5/2 DCV
? 5/3 DCV
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? Rotary spool type
? Check Valve
? Shuttle valve
? 2/2 DCV
? 3/2 DCV
? 4/2 DCV
? 4/3 DCV
? 5/2 DCV
? 5/3 DCV
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? Rotary spool type
? Check Valve
? Shuttle valve
? 2/2 DCV
? 3/2 DCV
? 4/2 DCV
? 4/3 DCV
? 5/2 DCV
? 5/3 DCV
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? Rotary spool type
? Check Valve
? Shuttle valve
? 2/2 DCV
? 3/2 DCV
? 4/2 DCV
? 4/3 DCV
? 5/2 DCV
? 5/3 DCV
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? Rotary spool type
? Check Valve
? Shuttle valve
? 2/2 DCV
? 3/2 DCV
? 4/2 DCV
? 4/3 DCV
? 5/2 DCV
? 5/3 DCV
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? Rotary spool type
? Check Valve
? Shuttle valve
? 2/2 DCV
? 3/2 DCV
? 4/2 DCV
? 4/3 DCV
? 5/2 DCV
? 5/3 DCV
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? Rotary spool type
? Check Valve
? Shuttle valve
? 2/2 DCV
? 3/2 DCV
? 4/2 DCV
? 4/3 DCV
? 5/2 DCV
? 5/3 DCV
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? Rotary spool type
? Check Valve
? Shuttle valve
? 2/2 DCV
? 3/2 DCV
? 4/2 DCV
? 4/3 DCV
? 5/2 DCV
? 5/3 DCV
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Flow Control Valve
? The valves which are mainly used to
regulate the flow of fluid in
hydraulic circuits are known as
“flow control valves”.
? Flow control valves are used to
control the amount of oil supplied
to various parts within a hydraulic
system.
? The momentum of a cylinder or the
rotational speed of a hydraulic
motor can be controlled.
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Types of Flow Control Valves
? Gate valve
? Plug valve
? Butterfly valve
? Ball valve
? Needle valve
? Globe valve
? Pinch valve
? Diagram valve
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? Gate valve
? Plug valve
? Butterfly valve
? Ball valve
? Needle valve
? Globe valve
? Pinch valve
? Diagram valve
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? Gate valve
? Plug valve
? Butterfly valve
? Ball valve
? Needle valve
? Globe valve
? Pinch valve
? Diagram valve
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? Gate valve
? Plug valve
? Butterfly valve
? Ball valve
? Needle valve
? Globe valve
? Pinch valve
? Diagram valve
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? Gate valve
? Plug valve
? Butterfly valve
? Ball valve
? Needle valve
? Globe valve
? Pinch valve
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Pressure Compensated Flow Control Valve
? Flow of hydraulic oil flowing through an orifice depends on the pressure
difference across the orifice, hence flow of hydraulic oil flowing through
the orifice or valve will also vary due to variation in pressure difference
across the valve.
? Speed of hydraulic actuator will vary due to variation in flow rate of
hydraulic oil entering or leaving the actuator because speed of actuator
depends on the flow rate of hydraulic oil leaving or entering the actuator.
? Non-pressure compensated flow control valves could not be used with
hydraulic actuators that must actuate with constant speed.
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Pressure Compensated Flow Control Valve
? Hydraulic actuators to move with constant speed, regardless of pressure,
pressure compensated flow control valves will be used.
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Pressure Control Valves
? The force of a cylinder is proportional to the pressure in a system and the
area over which the pressure is applied.
? Controlling the pressure level in a circuit will therefore allow us to control
the output force of a cylinder.
? Pressure control valves control the max pressure level and also protect the
circuit from excessive pressure
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Types of Pressure Control Valve
? Pressure Relief Valves
? Direct acting pressure relief valves
? Pilot operated pressure relief valve
? Pressure Reducing Valve
? Unloading Valve
? Counter Balance Valve
? Sequence Valve
? Brake Valve
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? Unloading Valve
? Sequence Valve
? Brake Valve
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? Unloading Valve
? Sequence Valve
? Brake Valve
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? Unloading Valve
? Sequence Valve
? Brake Valve
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? Unloading Valve
? Sequence Valve
? Brake Valve
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Difference b/w Pressure Relief & Unloading
Valve
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? Unloading Valve
? Sequence Valve
? Brake Valve
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? Unloading Valve
? Sequence Valve
? Brake Valve

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? Unloading Valve
? Sequence Valve
? Brake Valve

Proportional Valves
? A proportional valve provides
a change in output pressure
or flow in the same ratio as
the change in the input.
? If the input doubles then the
output will also double.
? Proportional valves can be
interconnected with the
output from one being used
as the input to another.
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Servo Valves
? Servo Valve is Direction
Control Valve
? Can Control both
Direction and amount
of flow
? It is coupled with
feedback sensing unit
for accurate position
control
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Block Diagram – Servo Valve
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Mechanical Hydraulic Servo Valve
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Hydraulic Actuators
? An actuator is used to convert the energy of fluid back into the mechanical
power.
? The amount of output power developed depends upon the flow rate, the
pressure drop across the actuator and its overall efficiency.
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Types of Actuation
? Linear actuator
? Rotary actuator
? Semi Rotary actuator
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Linear Actuators – Hydraulic Cylinders
? Single-acting cylinders.
? Double-acting cylinders.
? Telescopic cylinders.
? Tandem cylinders
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Single Acting Cylinder
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Double Acting Cylinder
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Telescopic Cylinder
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Cylinder Problems
Maximum thrust = Pressure × Rod area =
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Cylinder Mountings
?Centerline mountings
?Foot mountings
?Pivot mountings
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Cylinder Mountings
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Cylinder Cushioning
? Slows down piston at the end of the stroke.
? Lowers stress on cylinder by reducing
vibrations
? Improves service life of cylinder
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Cylinder Cushioning
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Hydraulic Motor
? Converts Hydraulic Energy
into Mechanical Energy.
? It produces rotation, torque.
? Pump can itself act as motor
? Types
? Gear Motors
? Vane Motors
? Piston Motors
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Hydraulic Pump Vs Motor
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Fluid Power ANSI Symbols
? Types of symbols commonly used in drawing circuit diagrams
for fluid power systems are Pictorial, Cutaway, and Graphic.
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