Troubleshooting - Emerson Fisher 785C Instruction Manual

Instruction Manual
D104483X012

Troubleshooting

Table 14. 785C Troubleshooting
Symptom
Inadequate operation of actuator using
handpump
Pneumatic stroking speed too slow for
actuator with handpump
Single acting spring return actuator will not
achieve full travel
Actuator movement not smooth
Valve positioner out of calibration during
fast stroking or high vibration
Common Possible Cause
Handpump control unit (key 2751) not in required
vertical up orientation per figure 7
Handpump hydraulic oil level too low
Too much air within hydraulic cylinder
Standard Stroke MHP handpump
Engagement/Disengagement handle at "Manual
Opening" or "Manual Closing" position
Fast Stroke MHQ handpump hydraulic cylinder bypass
stop valve at close position
Flow restriction in hand pump or hydraulic system
affecting actuator stroking speed
Flow restriction in pneumatic system affecting
actuator stroking speed
Actuator venting port blocked
Supply air pressure too low to fully extend/retract
actuator
Erratic, or jerky, actuator movement may indicate
excessive actuator or valve friction
Severe application conditions affecting positioner or
mounting kit
Solution
Contact your Emerson sales office
handpump control unit into correct installation
orientation per figure 7
Check and restore correct handpump hydraulic oil
level
Contact your Emerson sales office to bleed the
handpump hydraulic cylinder air
Set Standard Stroke MHP handpump
Engagement/Disengagement handle to "REMOTE"
position per figure 8 and the correct schematic
figure 12, 14, or 15
Open Fast Stroke MHQ handpump hydraulic cylinder
bypass stop valve per the correct schematic in
figure 11, 13, 16, or 17
Contact your Emerson sales office to upgrade to 785C
Fast Stroke MHQ handpump type 1 or type 2
Contact your Emerson sales office to investigate the
stroking speed sizing problem
Clean venting side vent assemblies, e.g. Y602 vent
Increase supply air pressure back to actuator sizing
required pressure
Contact your Emerson sales office to complete
ValveLink scan of actuator and valve movement to
identify if valve or actuator repair is required
Contact your Emerson sales office to investigate the
issue, and determine if upgrading to the high
performance mounting kit is recommended
785C Actuator
May 2022
to modify the
35