Sierra 840 User Manual

Series 830/840/860 Instruction Manual

Chapter 5 Troubleshooting

IM-83/84/86-H

5-3

Flow Controllers with Motor-operated Rotary Valves

Problem

Possible Cause

Solution

Valve “hunts” back and forth
continuously

Pressure differential too great

Motor coupling set screws loose

Valve motor failure

Reduce pressure

Tighten set screws

Replace motor

Valve rotates continuously

Limit switch out of adjustment or bro-
ken

Microprocessor failed

Adjust or replace switch

Replace microprocessor

Valve does not rotate

Contaminant blocking valve

Motor fuse blown

Remove blockage

Replace 1 amp fast blow fuse on
motor valve board

Flow reading is erratic

Inlet filter screen clogged

Clean or replace screen

Reads full scale with no flow or
with valve shut

Defective sensor

Q1 shorted

U10 failed

Return to factory for replacement

Replace with same type part

Replace with same type part

Flow does not match set point
within specifications

Insufficient pressure differential

Increase pressure or reduce set
point