Page 322 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

Scotch yoke actuator
This actuator uses a Scotch yoke mechanism for its operation and converts linear force into torque to motorize
the quarter turn valve. Two configurations are available – “single acting and double acting”. Scotch yoke actuator
consists of 2 main components – housing containing the yoke mechanism, pressure cylinder containing the piston.
In signal acting type, spring also becomes a part of it, where in double acting there is no spring and air pressure
is required for both closing and opening. The diagram of Scotch yoke actuator is shown below-
Scotch yoke actuator

Vane actuator
Vane actuators are basically true rotary pneumatic actuators and do not require converting linear motion to rotary
motion. They are used to open, close or modulate quarter-turn valves, dampers, louvers and the inlet guide vane
(IGV) of a compressor or turbine as well as for the precise operation of ergonomic lifting equipment. Vane actua-
tors are designed to connect to direct valve devices to transfer shaft movement. The diagram of vane actuator is
shown below-

Vane actuator

Single acting actuator or Spring actuator-
In a single acting actuator, control pressure is applied to an inlet port of the actuator to operate/open the valve,
and valve closing is determined by the stored energy of the spring. Therefore single acting actuator is also called
spring actuator. To close the valve, the applied pressure is reduced proportionally and is directed by spring return
/ spring release. There are two types of possible actions (without use of air lock relay) –

direct acting actuator (apply pressure to open/close)

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CITS : E & H - Electronics Mechanic - Lesson 188 - 198