Mains water isolated from the street, but tap still running?

[gregch]

Hello folks. So our mains water supply pipe got severed (not by me) and temporarily replaced so working fine but lying on the surface. Now have the new trench dug and new MDPE supply pipe and correct fittings all ready to go.

I've been out to the street (new-ish square plastic box with meter in and isolation valve-type stopcock) and shut off the mains supply (meter stops). Then I've gone in and run the kitchen tap to double check and weird stuff happens. The flow slowed right down to a trickle, then started to run again!

The property has an accumulator which stores 100l of mains-pressure cold water. Is it possible that, having shut off the mains supply, water is flowing back out of the accumulator through the kitchen tap?? (it's hard to trace, but I would have thought the accumulator would only feed the bathrooms, and there should be a non-return on its inlet??).

All input gratefully received!

 

[Lower]

How long did it continue to run for?

There will be some residual water in the pipes that feed the storage tank and any upstairs take offs that are mains fed. That water will come back down the pipes from gravity, particularly if there is an open ball valve in the storage tank.

 

[gregch]

It was still running after 5-10 mins, when I decided to give up, turn the mains back on and seek advice. That seems too long for just water in the pipes, but perhaps not long enough to drain a 100 litre accumulator (if that is how the accumulator works??).

 

[Madrab]

Nope, keep running it, especially if you have an accumulator, it will stop eventually. Depending on the mains pressure the accumulator can run for quite a while.

 

[gregch]

Ah right, thanks! Is it likely I'll need to reset pressure on the accumulator after its been emptied and refilled, or should that just take care of itself as it was??

 

[Madrab]

Wouldn't think so, accumulators are basically expansion vessels, the mains slowly fills the accumulator, pressing against the bladder inside and compresses the air/gas. When the tap is opened the bladder is under pressure and pushes against the water, supplying the outlets with a constant pressure and flow until it's exhausted.

 

[gregch]

Excellent. I'll give it a go and see. Thanks for the help!

 

[gregch]

Sorry to resuscitate an old thread; I went away before I could do this job and then lockdown etc, but back now and about to give it another go...

Possibly about to ask something very stupid indeed. Is there any need to wait for the accumulator to empty, or could I just shut off the stopcock in the house?

I guess if I did shut off the stopcock in the house, there would be no way for me to empty the water in the pipe between the street stopcock and house stopcock (by opening a tap), that bit of water would just escape into the trench/garden which would be quicker but a bit messy...!

Whereas if I close the street stopcock but leave the house stopcock open, I can drain down the whole house (and accumulator) and the pipe will be empty. What's best?

 

[Alec_t]

Whereas if I close the street stopcock but leave the house stopcock open, I can drain down the whole house (and accumulator) and the pipe will be empty.

Why do you want to drain the pipe between street stopcock and house stopcock?

 

[gregch]

Ah, because that's the section of pipe (mains supply up front garden) that needs to be disconnected so it can be cut to length and put into the trench.

 

[Garfeild]

If you shut off the street stopcock and the house stopcock, you will not lose all the water in the accumulator, there will only be a little bit in the pipe between the two valves, which is very little, then just relay the pipe between the two, job done.

 

[gregch]

Excellent, thanks. I think I'll do it like that - shut off both street and house stopcocks, take the temporary pipe off and let the water in the pipe escape, then fit the new pipe, turn on both stopcocks, check for any leaks and then backfill the trench.