Dwyer 38R - Manual (Page 10)

Series 38R ••• Self-Acting Temperature Control Valves Operation, Installation & Maintenance Manual
Page 10
CHECKING THE REGULATOR FOR PROPER ACTION
The thermal actuator will become inoperative if any leak occurs in the thermal system, allowing the pressure to
escape from the system. This will in turn cause the bellows to retract upward causing the regulator to control
as if the measured process had turned very cold. i.e. A heating valve will fully open and a cooling valve will
fully close. (See section on Option 3 for different response of “Fail-Safe” actuator.)
CAUTION:
NEVER SEPARATE YOKE FROM CAP.
Removal of the four screws can cause injury due to
the rapid expansion of pressurized bellows and captive spring tension.
INSPECTING the Actuator
On the Option 2 Actuator the dial thermometer is an integral part of the thermal system. To check the thermal
system for action simply read the dial thermometer. If, with the valve still attached, the dial thermometer is reading
a proper temperature the actuator is good. If the dial thermometer is reading a very low temperature, possibly
completely off of and below the scale, then the thermal system is most likely dead and needs to be replaced.
On all other model of actuators:
1. Record the current adjusting screw setting relative to the reference scale.
2. Set the adjustment screw to approximately “5” on the reference scale.
3. Remove the sensing bulb from the thermowell or process.
4. Subject the sensing bulb alternately to temperatures near the high and low limits of the nominal range of the
instrument. This nominal range can be found on a tombstone shaped aluminum tag hanging from the
tubing.
5. If stem motion up and down of over a 1 / 4 ” is observed then the actuator is good.
6. If no motion is seen, remove the actuator from the valve body. See section on “Removing Valve Body
Assembly”.
7. Repeat steps 2 – 5.
8. If no motion is seen, then the actuator is dead and needs to be replaced.
A) Obtain a replacement actuator and install onto the existing valve.
(See section on“Replacing Valve Body Assembly”)
B) Finish re-installation of actuator and set adjusting screw to previously recorded reference number.
C) Restart as if a new installation per this instruction manual.
9. If motion is seen, the actuator is good. Set adjusting screw back to recorded reference mark and then
inspect the valve for proper operation.