There are several modes of failure for a BFW leak off valve. They can fail due to seat leakage casuing micro cavitation whilst in the shut position. The solution here a valve that has drop tight seat leakage such as some of the metal seated ball valves (VTI) with a downstream inline diffuser (Mitech) to dissipate the pressure. However, in your case it sounds as if the damage occurs during operation. I assume that you are operating these valves in a modulating mode rather than on-off. A disk stack valve would be the solution if it were not for the flashing that is taking place. The best solution to that is to put a restriction orifice in the line as close as possible to the condensor. To ensure that the flashing always takes place across the orifice the flow rate must be constant - thus the valve should be operated in on-off mode bringing the solution back to the metal seated ball valve plus inline diffuser.

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