Cashco C27 - C53 Actuator User Manual

Page 7

IOM-C27-C53

2. Air Leakage; Direct action units. Diaphragm removal/replacement per Section IV. MAINTENANCE in its entirety.

Symptom

Cause-Remedy

Leakage at diaphragm-to-upper casing joint or thru vent
plug.

A1.

A2.
A3.

Overpressure. Check source of air supply and determine
if pressure is greater than indicated in Technical Bulletin;
reset airset pressure as required.
Tighten fl ange bolting.
Faulty seal at stem-diaphragm-seal joint. Remove upper
case - diaphragm washer. Install new o-ring (15).

SECTION V

V. TROUBLE SHOOTING GUIDE

NOTE: Cashco, Inc. recommends that if the casings are unbolted, the diaphragm, o-ring and TFE tape guide bushing

should always be replaced.

1. Air Leakage; Reverse action units. Diaphragm removal/replacement per Section IV. MAINTENANCE in its entirety.

Symptom

Cause-Remedy

Leakage at diaphragm-to-lower casing fl ange or thru vent
plug.

A1.

A2.
A3.

Leakage from around stem and attachment hub.

Replace O-ring (17).

3. Unstable

stroking.

Symptom

Cause-Remedy

Intermittent screaching noise, jumpy motion; positioner/
controller loading stable

A1.

A2.

A3.

A4.
A5.

Excessive valve packing friction. Maintain valve packing
per valve instructions.
Misalignment of valve stem-to-actuator stem; realign per
valve instructions.
Excessive valve guide wear. Maintain valve per valve
instructions.
Flow induced instability thru valve. Stabilize
Install high range spring in actuator; i.e. increase bench
setting level.

Positioner output unstable; positioner input signal stable.

B1.
B2.
B3.

Refer to the positioner IOM
Reduce positioner gain.
Re-calibrate positioner.

C. Controller output signal unstable.

C1.

C2.

Stabilize controller by increasing proportional band,
adding reset, adding rate, or combinations of all.
Unstable process. Snub process if able. Stabilize process.