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Next dumb question - changing ballcock in loft tank

Postby sfjnet » Mon Jun 23, 2008 8:42 am

Hi, You guys have helped me a couple of times now so that I have been able to do simple plumbing jobs myself, and I'm hoping you can do it again. The ballcock in my loft cold water tank needs changing - when filling the tank the old one sometimes makes a terrible vibration noise that echoes through the house. I have the new unit and it looks extremely easy to fit it, but my problem is removing the old one. I expected to find copper pipe for the mains cold water into the tank, but instead it is a flexible black pipe (HDPE?). I think I would know what to do if I found a regular copper fitting, but I'm not quite sure how to treat the connector on the end of the flexible pipe. I have posted photos of the feed pipe and also the existing ballcock fitting inside the tank via the link below. Should I loosen the large part that is connected to the flexible pipe? I don't want to mess anything up and end up with a leaky feed pipe. Thanks so much as usual.

Photos of feed pipe and inside tank:
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Simply Build It

Postby EyeTry » Mon Jun 23, 2008 11:26 am

When you draw water via the cold water header tank the ball / float follows the falling water level down and a lever arrangement opens the actual valve to allow water from the rising mains to then flow into the tank. As the level rises so does the ball and the lever gradually closes the valve as the ball reaches it`s maximum level. If the incoming pressure is high it may try and overcome the closing effect - rather like someone trying to push open a door against someone who`s trying to close it. A test of strength causes the door to bang shut / be forced open / bang shut.... .
SO FIRST - Try opening OR closing the household stop cock a half or one turn (or any gate valve / service valve in that supply pipe to the tank) and see if that change in pressure reduces or solves the problem.

If it doesn`t then close the supply valve or stop cock and drain off some water from that pipe by opening the kitchen cold tap. Pushing the ball down into the water in the tank will confirm whether you`ve stopped the supply or you need to find another stop cock or service valve to stop the supply. Might be a good time to fit a service valve near the tank "for the future".

The actual valve assembly fits through the wall of the tank (washers either side) and a nut wound along the threads on the outside secures the whole thing (make sure the ball arm can rise and fall vertically before you re-connect the pipework, if it tries to lift out of the vertical it may jam and water would continue coming in via the valve).

Your picture seems to show another coupling on the inside of the tank.... If your new valve assembly is the same just check if you can separate the new assembly at that point. If so then you may be able to leave the pipe joint untouched and just replace that internal part of the assembly.

However if you do need to disconnect the whole assembly then you will need to disconnect the pipe joint. If it is a rigid plastic pipe there will be an olive or collet that is squeezed into the pipe and the end of the valve assebly as you tighten the nut/coupling (compression joint fashion). If it is a more flexible plastic then it may have a plastic or metal insert inside the end of the pipe (to prevent it being distorted by the tightening of the nut/coupling)

Make sure you use a spanner /wrench on the nut or coupling AND a second one on the assembly otherwise pressure applied to just one may twist the whole thing rather than unscrewing or screwing one part. Good Luck, Eye Try
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Postby thedoctor » Sat Jul 06, 2013 9:20 am

A very old post, we know, but still hugely popular. Doesnt seem to matter how good the tech gets, the same old problems keep cropping up ! There is some great info on tanks and valves etc on this link if you want some answers. ... %20etc.htm
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