Fitting new bypass/isolation valve - how to secure fitting

20 Oct 2013
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United Kingdom
Hi all - I have a water softener with a bypass/isolation valve, but it is plastic and old, and has a crack in it, so needs replacing. I've been given a new metal one which I'd like to fit myself. However out of the box, none of the fittings seem to be tight after screwing it together. I can just pull them all apart.

Photos are attached. There's not much to them. A thread at one end, a nut, and some sort of washer. If I attach them all together, I can just pull the fittings apart still with no effort.

Have I missed something really obvious? I thought this would be a simple DIY project but am I better off just getting a plumber out to do it? :D


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Which one is it you need to replace - none of them look like they're plastic.

These are compression fittings. The 'washer' is an olive and that needs to be mechanically compressed by the nut, that will require tools, usually adjustable spanners. if you aren't sure then, yup, it may need a plumber.
1. Measure (accurately) the diameter of the plain, unthreaded, spigots you are trying to insert into the valves.
2. If this is 22 mm, then just tighten the compression nuts up, with the olives in place. Start at finger tight plus 1/3 to 1/2 turn with a spanner, and nip up a bit more if they weep slightly when connected. You need two spanners, one to hold the valve (hexagonal part just before thread at one end only) and one to do up the nut. They are not the same size, so two adjustables, or one adjustable and some grips, are needed.
3. If it is just under 21.5 mm (hence the need for accurate measurement) then you need to replace the olives with 3/4" to 22mm olives. See for details.

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