DeZURIK
PMV P36C and P41C Positioners
used with DeZURIK Pneumatic Actuators
August 2012
Page 5
D10327
Description
The positioner is a precision instrument which, when used in conjunction with a DeZURIK actuator, can
provide the exacting control necessary to satisfy the most demanding process requirements.
The model P36C will accept a 3-15psi, 3-9psi, or 9-15 psi input signal.
The model P41C will accept either a 0-20mA or a 4-20mA input signal.
The modular design allows for easy parts replacement, and quick access to Zero and Span
adjustments. The housing uses an O-ring seal that can be adjusted to a sealed or drained position.
Operation
P36C and P41C positioners operate on a force balance principal. Force is applied from a signal
pressure that is transmitted through a diaphragm (1) to the balance arm (2). The feedback spring (3)
provides the opposing force. This force is proportional to the level of the lower arm (4). The lower arm
level is determined by the position of the cam (5), which is secured to the spindle (6). The spindle is
connected to the actuator shaft thus providing the feedback from the actuator and valve. See Figure 1.
When the opposing forces are equal, the balance arm (2) and the spool in the pilot valve (7) are in
neutral position and the complete system is in a balanced condition.
Figure 1 – Internal Parts
Air is supplied through port S to the pilot valve, which controls air flow through ports C1 and C2.
Starting from a balanced condition, an increased control pressure will deflect the diaphragm (1) down,
compressing the feedback spring (3). The balance arm (2) moves the spool (7) in the pilot valve (8)
thus supplying air to the actuator. At the same time air is exhausted from the actuator and vented to
atmosphere through the pilot valve and the OUT port.
Air pressure to the actuator is increased, causing the actuator to move the valve and the positioner
spindle (6). The spindle and cam (5) rotate, forcing the lower arm upward, compressing the feedback
spring (3). This motion continues until the two forces are equal and the system returns to a balanced
condition.
