"Rod" wrote in message
...
The other day I replaced an old and leaking stopcock under the kitchen
sink - with a proper full bore valve.

However, once I had done that, I found that there was a horrific bang
every time I turned the tap off other than *very* slowly and gently. So,
at least as an interim solution, I closed the new valve down a bit - and
reduced the bang considerably. (That is, it would only happen when really
trying.)

Then I realised that the other water in the house that is fed directly
from the mains (one WC cistern and the cold water tank and CH
header/expansion) were also very prone to banging - which was new.

On to the next idea - when I had turned off the mains to do the job, had I
inadvertently turned it up higher when restoring water? Well - no. I
checked before turning it off - it was fully open - and back half a turn.

So I have now turned the under sink full bore valve full on and turned the
mains stopcock down. (Currently a bit too far - at about half-to-one turn
from fully closed.) Even at this setting the flow is pretty good.

As I had been working on the kitchen sink, there had been a couple of vans
and around half a dozen people on the main road nearby. They had been
staring at some water utility 'holes' - the covers of some were open. The
vans were marked with "PRV Maintenance" and a company name (one of the
outsource the work outfits that do most of the work for the utilities -
but I have forgotten which one). Looking up PRV I found only one related
meaning - Pressure Reducing Valve. Could they have done something like
turn up the pressure?

Make any sense to anyone?

Fit in a full-bore mains stop-tap. Then near the kitchen sink tap fit a
small shock arrestor which cost around £10. Sorted.