IM-P006-07 CTLS Issue 12
27
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 2.
4. The point at which the external pressure sensing pipe is tapped into the main is in a turbulent area.
Refer to Section 2.8 for guidance.
5. Loose dirt in the pipe assembly. Remove the pipe assembly and blow it through to clear it.
6. Pilot valve or pilot valve plunger is sticking. Follow steps in Section 5.5.
7. Main valve pushrod sticking. Follow steps in Section 5.9.
8. Pilot diaphragms or main diaphragms overstretched. To replace, see Sections 5.7 and 5.8.
To Next Page
Loading...
