23
Model 752 and 752A Differential Pressure Transmitters
Section 4
4.
Replace the housings (new O-rings are recommended) and 3/8" CRES
head bolts.
5. Apply Molycoat G paste or similar lubricant to threads and under heads
(bearing surface) of bolts. Do not use silicone oil or grease.
6. Torque the head bolts to 45 ft-lb to a rotation of up to 135 degrees nomi-
nal using a torque wrench. The rotation of the bolt is measured after the
bolt is "snug" with approximately 2 ft-lb torque.
Note:
Do not exceed the specified rotation. If a bolt fails to reach the specified
torque within the rotation limit, reject the bolt.
Troubleshooting
Refer to Tables 4.3 and 4.4, pages 21 through 23, for troubleshooting infor-
mation and Section 5 for part location.
Note:
If the sensor assembly is determined to be faulty, the transmitter should
be returned to the factory for repair or replacement.
Table 4.3—DPU Troubleshooting
Problem
Possible
Source
Probable Cause
Corrective Action
Low or No
Output
Primary
Element or
DP Source
Orifice installed backwards or
oversized;
Flow blocked upstream from run;
Density changes in process
media or ref. leg
Replace orifice;
Clean out run or
open valve;
Refill reference leg
with same density
liquid as process
Piping from
Primary
Element to
Transmitter
Pressure tap holes or piping
plugged;
Bypass valve open or leaks;
Liquids or gases trapped in pipe;
Block or shutoff valves closed;
Piping leaks, high pressure side
Clean out piping;
Close bypass valve;
Vent piping;
Open block or shut-
off valves;
Repair leaks
Bellows Unit
Housing filled with solids restrict
-
ing bellows movement;
Gas trapped in housing in liquid
service or liquid trapped in hous-
ing in gas service;
HP housing gasket leaks;
Body tampered with
Clean out housing;
Vent housing;
Replace gasket;
Return unit for
repair