27
Model 289A Differential Pressure Indicating Switch
Section 3
Table 3.2—Troubleshooting
Problem
Possible
Source
Probable Cause
Corrective
Action
High
Indication
Primary
Source
Orifice partially restricted or too small
Clean out or
replace
Primary
Element to
DPU piping
Piping leaks on LP side
Repair leaks
Bellows
Unit (Refer
to DPU
Manual)
Gas (liquid service) or liquid (gas ser-
vice) trapped in housing
Vent housing
LP housing gasket leak
Replace gasket
Range spring broken or DPU tampered
with
Return BUA for
repair
Indicator,
Alarm-
Switch
Mechanism
Loose linkage or movement
Tighten or replace
Out of calibration
Calibrate
Erratic
Indication
Primary
Element
Flow pulsating
Install dampening
device upstream
of DPU run
Primary
Element to
DPU piping
Liquid (gas service) or gas bubble
(liquid service) trapped in piping
Remove
Vapor generator incorrectly installed
Re-pipe
Reference leg gassy or liquid vapor-
izing
See piping
instructions in
DPU Manual
Bellows
Unit
(Refer
to DPU
Manual)
Obstructed bellows travel
Clean bellows
Gas trapped in DPU HP or LP housing
Remove (see
startup proce-
dure)
Linkage dragging or dirty
Adjust or clean
Pointer dragging on scale plate
Adjust pointer
position
Inaccu-
rate or No
Electrical
Alarm
Power
Supply
Blown fuse
Replace fuse
Broken or loose wire
Repair
Alarm
Switch
Switch not properly adjusted
Adjust switch
Dirty or burned
Replace switch
contacts