Pressure puzzle

[Gonzo1489]

Evening folks, Got a bit of a headache trying to figure this out.
Blue pipe incoming mains - stopcock - prv - 2 external garden taps one front and one rear. Prv is reading 2.6 bar. Confirmed this with a meter on the dishwasher feed. One garden tap reads 2.6 bar. The other 3.7 bar. How can this be possible as everything is switched off with the mains stopcock, so no tee off before the prv.
Any ideas??
TIA

 

[reds42]

Outside tap got a check valve in it (it should have)? If so possibly when you turned the tap on with the meter connected you got a bit of water hammer, and the pressure increase from the shock wave was captured by the check valve.

 

[Gonzo1489]

Good shout thanks. I’ll stick a new tap on and see what happens.

 

[reds42]

You could just try turning the tap on very, very slowly to avoid the sudden rush of water which suddenly stops that causes water hammer.

 

[Madrab]

Outside tap got a check valve in it (it should have)

Should it? Thought they were taken off the WRAS registered as they were found to be freezing up and destroying the plastic check valve so it's back to inline double check valves on the internal pipework after the ISO?

 

[reds42]

Should it? Thought they were taken off the WRAS registered as they were found to be freezing up and destroying the plastic check valve so it's back to inline double check valves on the internal pipework after the ISO?

I stand corrected if that's the case.

 

[oldbuffer]

1. New installations of outside taps should have a check valve (and isolation valve and drain off point) inside the thermal envelope of the property.
3. Existing installations, where the check valve is built into the tap, can have the tap replaced by another with built in check valve. It is still better to use a necessary outside tap replacement up to the modern standard.