Spirax Sarco DP27, Инструкция по установке и обслуживанию

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IM-P470-03
CH Issue 7 37
7.3 Downstream pressure too high
If the pressure on the downstream side of the reducing valve has risen above the required
set pressure check the following:
1. Downstream pressure sensing pipe blocked. Dismantle and blow through.
2. Control orifice (item ' P1 ' on page 29) blocked. Unscrew pipework from side of body and
clean out. For identification this coupling has a groove around the hex.
3. Pilot valve diaphragms fractured.
Check and replace (see Section 5.6).
4. Pilot valve or pilot valve plunger is sticking. Follow Steps 6 to 9, Section 5.4.
Check as Section 5.4, Steps 6 to 12
5. Main valve not seating.
Check and replace (see Section 5.8).
6. Main valve pushrod sticking. Follow Steps 27 to 34, Section 5.7.
7. Pilot valve plunger too long.
Check as Section 5.4, Step 9.
8. Pilot valve not seating.
Check as Section 5.4, Steps 6 to 12.
7.4 Hunting
Hunting may coincide with variations in steam load. If this is the case, the following checks
should be made before dismantling the valve:
1. Check that the upstream pressure is stable. If the pressure drops during full-load
conditions, it is possible that there is a partial blockage upstream, or that the upstream
pipework is undersized. If the upstream pressure is low, the effect will be to reduce the
capacity of the valve with the possibility of not maintaining the downstream pressure
during full-load conditions.
2.
If the upstream pressure is correct, and stable, set the valve on dead-end conditions.
Apply full-load to the valve.
If the downstream pressure drops excessively during full-load condition, it is likely that
the valve is undersized, in which case it should be replaced.
Once it has been determined that the upstream pressure is correct and stable, and that
the valve is correctly sized, the following check should be carried out on the valve:
3. Steam is very wet. Ensure the valve installation is as recommended in Figure 4, page 12.
4. The point at which the external pressure sensing pipe is tapped into the main is in a
turbulent area. Refer to Section 3.8 for guidance.
5. Loose dirt in pipe assembly (Item ' P ' on page 35). Remove pipe assembly. Blow through
to clear.
6. Pilot valve or pilot valve plunger is sticking. Follow Steps 6 to 9, Section 5.4.
7. Main valve pushrod sticking. Follow Steps 27 to 34, Section 5.7.
8. Pilot diaphragms or main diaphragms overstretched.
To replace, see Section 5.6, page 24.