In article 6,
DerbyBorn writes:
I really want to replace it all - one end compression is a bit crusty as
well. I don't want to leave a legacy of bodge! I want to cut a lenght out
and fit new valves with new pipe in between.

Are double check valves essential?

They are required if there's any risk of feeding back into water
supply. For a shower, that means if the hose is long enough and
positioned such that the shower head can be under water in a bath
and thus syphon water back into the mains. Wouldn't apply to a
shower tray with no waste plug.
It would also apply if the hot water comes from a storage tank and
the cold water from the mains.
Some shower valves include them anyway (typically those with
separate temperature and flow knobs, where the flow knob is on the
mixer outlet, and those with hot/cold differential pressure
compensation for use with multipoints and combis).

Essential? Depends what you regard as essential. They can
significantly impede the flow if the pressure isn't very high.

--
Andrew Gabriel
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