Problem with sealing joint plastic-brass (again)

[Scrumpy User]

Hi folks

I've seen that this topic has come up before, but I'm stumped as to what to do. I'm trying to fix a leaky joint between a lavatory cistern ball-valve and the water supply.

The ball-valve inlet has a plastic or nylon tail, and the connection to the water supply is by a brass tap connector. It's been working fine for years but recently developed a slow leak.

I've tried replacing the fibre washer on the tap connector with firstly a nylon one and then a rubber one (I had to more or less make the latter from a larger washer, as I couldn't find one the right size anywhere. I've read the comments here that the fibre washers don't work too well with the plastic tail. I thought the nylon one might work better, but it didn't seem to.

The best I've been able to get it is by putting some PTFE tape round the tail threads and using the nylon washer. Even then it still leaks. I've tightened it to the point where I'm scared to tighten it any more for fear of breaking the plastic part.

I've now resorted to putting some of that radiator repair sealent (the stuff that's a bit like plasticine or putty, and hardens, not just boss white type stuff) around the nut on the tap connector, hoping it will stop the leak.

I don't like doing this osrt of bodge and at the time of writing I don't even know if it will work.

Is there anything else I could try? I realise I could replace the ball-valve with another one and start from scratch, but I don't have any confidence it will work any better. I can't see any obvious problem

- the existing tail looks flat at the end, the threads look OK, the brass parts look fine with no damage to anything.

Any further advice would be much appreciated! I've never had this type of problem before in years of (admittedly amateur) plumbing jobs.

Cheers

Scrump

[Lee]

You said the plastic tail looks ok, but maybe the plastic is deforming or a crack is developing as you tighten the connector up?

I'd try some LS-X or similar silicone sealant, then replace the tail ;)

Lee

[Harry Bloomfield]

Scrumpy User formulated the question :

Try an O ring, these are reasonably soft and deform to provide a seal, but also check that the nylon part has not cracked or split.

[Mr Fuxit]

I've had this problem many times. You will find that the water is leaking from between the threads on the plastic tail, caused by misalignment of the copper fitting with the plastic. It's easy to force the copper into line with the plastic in order to tighten the joint, but when the pressure is removed from the copper it loads the whole joint. Well, the coppers not going to give, so the plastic thread outside the joint bends and starts to leak, usually just inside the copper nut. Use a flexible tap fitting, and all youir problems will be over!

[Scrumpy User]

Thanks for the advice so far. My bodged repair doesn't work, so I'm going to have to do something to sort it out properly :(

I did think of using an O ring but I assumed thie wouldn;t work any better than a rubber washer. I could give it a try though.

Otherwise I might try and get a brass replacement for the ball valve, so I can just use a fibre washer. Seems a bit over the top but if you're desperate...! Pity my local B&Q only sells plastic ones

Cheers again

Scrump

[Mr Fuxit]

Sorry; in my previous post I should have said, "replace the leaking unit with a new one, and use a flexible tap connector".

[google]

Thanks to all for the replies. In the end I stripped the thread off the plastic/nylon valve through overtightening, so I had to get a new one. I fitted a flexible pipe as well, and it now works. I'll never know why it didn't work before though...

Cheers

Scrump