UNIT 2

ACTUATION SYSTEMS

Actuation Systems

• Pneumatic and Hydraulic Systems• Mechanical Actuation Systems• Electrical Actuation Systems

Hydraulic SystemsThere are basically three types of valves employed in hydraulic systems:• Directional control valves• Flow control valves• Pressure control valves

Direction control valve• Directional control valves are used to control the distribution of energy in a fluid power

system. They provide the direction to the fluid and allow the flow in a particular direction. • These valves are used to control the start, stop and change in direction of the fluid flow.

These valves regulate the flow direction in the hydraulic circuit. • These control valves contain ports that are external openings for the fluid to enter and

leave. The number of ports is usually identified by the term ‘way'. • The fluid flow rate is responsible for the speed of actuator (motion of the output) and

should controlled in a hydraulic system. This operation can be performed by using flow control valves.

• The pressure may increase gradually when the system is under operation. The pressure control valves protect the system by maintaining the system pressure within the desired range.

• The output force is directly proportional to the pressure and hence, the pressure control valves ensure the desired force output at the actuator.

Directional control valves

Type

of

cons

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tion:

Popp

et v

alve

s

Spoo

l val

ves

Num

ber o

f por

ts:

Two-

way

val

ves

Thre

e –

way

val

ves

Four

- way

val

ves.

Num

ber o

f sw

itchi

ng

posi

tion:

Two

– po

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n

Thre

e - p

ositi

on

Actu

ating

m

echa

nism

:

Man

ual a

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tion

Mec

hani

cal

actu

ation

Sole

noid

act

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n

Hyd

raul

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Pneu

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Indi

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Poppet Valve Spool Valve

Three way Valve• This valve has one pressure port, one tank port and one actuating port.• In this valve, the pressure port pressurizes one port and exhausts another

one and only one actuator port is opened at a time. • In some cases a neutral position is also available when both the ports are

blocked. Generally, these valves are used to operate single acting cylinders.

Four way valves

• It is generally used to operate the cylinders and fluid motors in both the directions.

• The four ways are: pump port P, tank port T, and two working ports A and B connected to the actuator.

• The primary function of a four way valve is to pressurize and exhaust two working ports A and B alternatively.

Pneumatic actuators

• Pneumatic actuators are the devices used for converting pressure energy of compressed air into the mechanical energy to perform useful work.

• Actuators are used to perform the task of exerting the required force at the end of the stroke or used to create displacement by the movement of the piston

• The pressurised air from the compressor is supplied to reservoir. The pressurised air from storage is supplied to pneumatic actuator to do work.

• There are three types of pneumatic actuator: i) Linear Actuator or Pneumatic cylinders ii) Rotary Actuator or Air motors iii) Limited angle Actuators

Rotary Actuator

• A rotary actuator is an actuator that produces a rotary motion or torque.

• Linear cylinder used to produce rotation

• Vane type semi-rotary actuator

• Vane Motor