Leaking flex tap connector

Hi All
I am fitting a new bathroom sink. I usually do this by fitting an isolation valve (one where you turn it on / off with a flat head screwdriver) between the incoming supply (terminated with a tap connector) and the flexible hose to the tap.
I am having trouble with one that constantly leaks no matter what I do. The tap connector side is fine but the connection with the flexible hose leaks. I have so far tried the following 1. The tap and hose came with a filter type rubber washer so used that first 2. Tried replacing that washer with a normal flat rubber washer 3. Put PTFE tape on the thread and used the washer.
All options still result in a leak. It looks like it is coming from the centre of the nut (as opposed to the thread) but can't be sure.
Anyone have any ideas what could be wrong?
Thanks
Lee
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I cannot quite picture your arrangement but if you are connecting your flex ible tap connector directly on to the isolator valve then I am not surprise d you are experiencing leakage problems. The isolator has connections that involve the use of an olive to provide the water tight seal the end of the thread has a chamfer on the inside to mate with an olive whilst the very en d does not have a flat surface to mate with anything tending to be rather s harp too.
What I suspect you need is something like these:
https://www.screwfix.com/p/tesla-brass-compression-adapting-flexible-tap-co nnectors-15mm-x-2-pack/2665r
The plain end goes in your compression fitting on the isolator with an oliv e off course and your tap connector on the threaded end with the rubber was her you mentioned initially.
A link to a photo of what you have got would help
Richard
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Sorry Richard should have mentioned that I file the ends of the isolation v alve flat before fitting. Wonder if this one I didn't do it enough. Will t ake a look at your fitting sounds like it is just the job although I hate c ompression fittings as mine take several attempts before they are sealed :)
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Lee Nowell wrote:

You can get combined flexible tab connector with isolator ...
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On 09/11/2019 16:35, Lee Nowell wrote:

Nobody seen these? Made for the job.
https://www.toolstation.com/tap-tail-adaptors/p14081
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Dave
The Medway Handyman
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On 09/11/2019 16:35, Lee Nowell wrote:

Nobody used these? Made for the job.
https://www.toolstation.com/tap-tail-adaptors/p14081
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Dave
The Medway Handyman
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On 09/11/2019 15:37, Tricky Dicky wrote:

Conversely I always use a normal full bore service valve with the backnut and olive removed to mate with the flexi connector, and have never had a leak. So long as the end of the valve is smooth and continuous, then it should seal against the flat washer. A narrower cross section just means it will seal with less torque.
I think in the OPs case I would replace the flexi.
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Yes also some of those flex things seem to have very deformable ends so when one does it up it can ovalise and end up leaking. I had one on our sink like that. Bah Humbug. Brian
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The tread is never part of the seal. The seal is the rubber washer (Probably damaged by overtightening) or an olive - but never the thread.
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Except, of course, when it is. Quite common with brass, 'iron' or mild steel fittings to similar metal fittings or pipes.
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Roger Hayter

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snipped-for-privacy@hayter.org (Roger Hayter) wrote in wrote:

Of course - but the use of PTFE tape on everything with a thread is not the solution to leaks. Most domestic modern applications - other than radiator tails will not use the fittings you suggest.
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e
Got to agree with you John, I have never found a compression fitting design ed to seal with an olive make a satisfactory seal with anything else no mat ter how much PTFE tape you put on the thread. A tap connector with a fibre washer no chance, a rubber washer I will grant you a maybe.
Richard
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Trouble with flexible connectors is a number of things can go wrong other t han the connection to a pipe fitting. As I think Brian has pointed out the rubber inner can fracture through age or overtightening and if this is an a lready used connector then it maybe a case of fixing it with a new one.
Richard
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On 11/11/2019 12:00, Tricky Dicky wrote:

Since compression fittings don't seal on the threads, that is not surprising.
PTFE on threads can serve a purpose as a lubricant however - sometimes making it easier to correctly tighten a coupling in a restricted space or with a short spanner etc.
However the issue I expect that was being take was with John's use of the rather absolute word "never", when there are a few examples of domestic plumbing fittings where you need to make a seal on the threads.
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The essentials of good fittings are: Cleanliness, No burrs or scratches, no cuts in washers.I cant help but think that ptfe as a lubricant is a bit of a comfort blanket / snake oil. Why not a spray of oil? Remember to witdraw a pipe from the compression fitting by a few mm before tightening so that both ends of the olive see the force (ie. The pipe is not bottomed)
In my house only the radiator tails need tape as they seal on the thread. I am just suggesting that people should consider - what is there to provide a clamping force and what is there to create a seal. Spending time trying to add stuff to the clamping medium when it is not the means of sealing is not a great idea.
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I had assumed that the pipe had to be all the way in to exert the nut tightening force in the olive.
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By backing off slightly, the tightning force will be applied to both sides of the olive. If the pipe is pushed all the way in then there is no movement possible at the inner end so nearly all the final deformation will be at the outer end of the olive. Think it through for yourself and see if you agree.
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And especially likely to catch you out if you use the same nut and olive on a new fitting (e.g. radiator valve) with a slightly shallower pipe recess; without excessive deforming force the side of the olive away from the nut will be held away ffrom the fitting by the length of the pipe. The remedy is to take mm or two off the end of the pitpe, but that is a nuisance.
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Roger Hayter

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snipped-for-privacy@hayter.org (Roger Hayter) wrote in

Good point.
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On 11/11/2019 13:03, John wrote:

I find it works well on the occasions that some lubrication is required, and also eliminates the loud squeak you can sometimes get on tightening compression fittings, which may be important in some circumstances.

Less mess, no risk of contamination in the water, and less chance of making the spanner surfaces of the nuts slippery.

I can't see that will make any significant difference. The nut will tend to compress the back of the olive and also drive it into the gap between fitting and pipe which compresses the front of it. The forces on both sides will be largely similar and in balance. From a sealing point of view its the front face that's closing the gap between pipe and fitting that is doing the work anyway.

I am sure the OP, has got that message by now.
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John.
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