A DCV wafer check valve installed in the main line
produces a small pressure drop, ensuring that a proportion
of the flow passes through the sampling chamber.
The DCV wafer check valve installed at the flash steam outlet from
the flash vessel, ensures that steam from the make-up valve does
not flow back into the flash vessel. The DCV wafer check valve after
the FT steam trap ensures that condensate does not flood back up
into the flash vessel.
When a blowdown vessel receives blowdown from more than one
boiler, a DCV wafer check valve should be installed on each
separate blowdown line. This will prevent the blowdown from one
boiler flowing back into another boiler. In many countries this is a
statutory requirement.