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7. Fault finding
7.1 Preliminary procedure
Before undertaking the following fault finding procedure, ensure the valve has been isolated
and that upstream and downstream pressures are zero. Possible fault checks are given in a
logical order below.
7.2 Downstream pressure zero or too low
If downstream pressure drops below set pressure or is zero check the following:
1. No high pressure steam reaching the reducing valve. Check that steam is turned on and
that the strainer is clear. (To assist with commissioning and fault finding it is recommended
to fit an upstream pressure gauge).
2. Pressure adjustment spring broken.
3. Pipe assembly (Item 'P' on page 29) blocked. Remove by uncoupling union nuts and blow
through to clear obstruction.
4. Control orifice blocked. Unscrew from outlet port and clear out obstruction. For
identification this coupling has a groove around the hex.
5. Main diaphragms fractured.
Replace diaphragms following Steps 27 to 34, Section 5.7.
6. Pilot valve plunger too short.
Check as Section 5.4, Step 9.
7. Valve capacity insufficient for downstream conditions.
a) Check that the upstream pressure is correct. If it is low, the capacity of the valve will
be reduced.
b) Ensure that the pressure sensing pipe is fitted as recommended in Section 3.8 and
if necessary fit an external pressure sensing pipe as described. If the downstream
pressure is still too low, then a larger valve with more capacity is required.
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