This procedure is intended for Fluke Calibration Employees, Approved Service Providers, or other authorized personnel trained on service repairs of 725x pressure controllers.
This shows how to disassemble the valves in a 725x pressure controller and check if there is wear or contamination on the sealing surfaces.
- Power off
- **Remove Supply Pressure - supply pressure is always supplied to one side of Apply valve.**
- Remove cover, use a razor knife to make a clean cut through tamper-proof seal(s) as they are difficult to remove. The round silver piece will unscrew but might require gently using pliers or similar.
- Remove black coil from valve. Make sure you're on the correct valve, and manifold if you have a 7252.
- Using open end wrench or 13mm deep socket to remove tube from sub base. Note that plunger, outer spring and a shim (control valves only) are inside the tube.
- Inspect seat and mating surface in sub base. Clean as needed. Apply very small amount of Krytox lubricant or similar to o-rings after cleaning.
- Remove screws to remove the sub base from manifold. Note the orientation, air flow holes in solenoid valves must align with air flow holes in the manifold block.
- Inspect o-rings on bottom of sub base and mating surface on manifold block. Clean with alcohol wipe as needed. Apply very small amount of Krytox lubricant or similar to o-rings after cleaning.
Valve orientation - The small valves are universal fit and will have 3 holes in the base that line up with the holes in the manifold. High pressure valves (large ones) have 2 holes and a drilled key hole that lines up with the hole in the manifold. The Isolation valve on the 7250xi controller also uses the large valve and has an arrow engraved on the base that points to the front of the controller.
See this article for valves used in 7250 and 7252 pressure controllers,
7250, 7252 valve and other part numbers
Valve coils - Coils that fit tightly on the tube usually have overheated at some time. They might fit well and have the correct resistance when cool. Generally if the inside tube of the coil that slides on the valve stem is white then it is good. If it's slightly reddish brown or brown, then replace the coil.
1 to 150 psi controllers use 9.3 watt coils in all 4 positions, PN 3915780.
150 to 1000 psi controllers use 9.3 watt coils for the REF and TEST ports, PN 3915780. 34 watt coils are used for the EXH and SUPPLY ports.
PN 3915800 34 watt coils should read 16 ohm ± 2 ohm
9.3 watt coils should read 62 ohms ±2 ohm.
Coil resistances increase slightly with temperature, this is normal.
The control sensor may have some particles of dirt, oil or thread tape in it. Try flushing with alcohol and thoroughly dry, or replace.