Installation, Operation and Maintenance Manual
MAN 575 Rev. 4
July 2020
3
General Warnings
Section 1: General Warnings
1.3
Introducing the Actuator
RPD actuators are pneumatic low pressure Spring-Return, suitable for any quarter-turn
application such as ball, plug, butterfly valves or dampers, in both ON-OFF and modulating
heavy-duty service. The actuator is made up of a rack and pinion mechanism, which
transforms the linear movement of the pneumatic cylinder, (on closing or opening), into
the rotary movement for the valve operation. An adjustable bronze sliding block supports
the transverse force exerted on the rack by its engagement with the pinion. The rack is
nitride for ensures the minimal friction. External travel stops allow precise angular stroke
adjustment between 80° and 100°. Totally enclosed, weatherproof housing, made of
nodular cast iron for maximum strength and suitable for use in hostile environments.
The mounting flange is identical on both (upper and lower) faces of the housing; the shaft
output drives have the same dimensions but is positioned at 90°. This allows the actuator
to be used as spring to close or spring to open without modification.
The actuator is assembled onto the valve by connecting the actuator housing flange to the
valve flange by a spool piece and the actuator shaft to the valve stem by a stem extension.
Actuator manual emergency operation in opposition to the spring action, is performed by
rotating the jackscrew by a wrench or by a handwheel (available on request).
