fittings confusion

[fluxeyfingers]

You can buy lengths of plastic in diy stores, cut it with a hacksaw and tidy up the ends with a stanley knife, hardly professional but it works (takes a bit of time though).

They look like 3/4 bsp tap tails, and these would do the job http://www.screwfix.com/p/flexible-tap-connector-15mm-x-3-4-x-500mm/96407 and the bore is large enough for a combi boiler.

 

[fluxeyfingers]

Ignore the second part of the last post - (blonde moment) - they actually look like 1/2''bsp which is unusual for a bath

 

[dalai]

help hear is first class thanks.

I'm pretty good with DIY but never plumbing before. have lots of tools incl. box & basin spanner.

Originally I was going to use

Flexible Tap Connector 15mm x 3/4" x 500mm (hot)

and

Flexible Tap Connector 15mm x 3/4" x 300mm (cold)

both have 15mm compression fitting to connect to existing isolation valve and ¾” BSP Female thread to connect to hot/cold taps.

Easy?

but screwfix say "We would not suggest that any flexible hose is a replacement for copper pipework, these are simply used within the industry to enable easy connection between taps and pipework, which may otherwise need altering to connect to new fittings. The bore on these products will always be smaller than the existing pipework that is there, however this should not have any adverse effect on the overall performance of the tap that they are connected to."








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Product Code: 96407










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[Belboz]

dalai.

I think what they are getting at is that such flexible hoses shouldn't be used in place of a normal run of pipework. Fine for connection between pipework and a tap - that's what they are there for.

Providing you have the size right (the tap end) then you can use compression or push-fit to the copper pipes after your iso valve.

Remember to leave enough room for the fitting after the iso valve and, if cutting with a hacksaw and using push-fit, ensure there are no burrs and the cut is straight. The former is not so much of an issue with compressions.

Check the run, isolate, connect the flexis and tighten up. Some on here may also suggest some PTFE (cheap as chips) on the fittings.

 

[fluxeyfingers]

Flexi hoses have been standard equipment on monobloc kitchen taps for years - the main reason they cause problems is on low pressure (ie, vented hot water) systems. As you have a combi it's mains pressure hot water, so unless your water pressure is particularly low, you'll be ok with 10mm bore.

If you have a DIY store nearby, you could nip in and pick up a 15mm compression coupler. This will have 1/2"BSP nuts (which aren't actually half inch in size) to compare to the ones on your tap so you know whether they're 1/2" or 3/4". 3/4 is usual for baths but I have seen 1/2" bath taps.

The combi can supply a maximum of around 9 litres/min of hot water, so add in a third cold and this leaves you with a figure of 14lpm or so for your shower (which is a reasonable shower).

How many litres/minute do you get from your kitchen cold tap (fill known size container, do a little maths)?

 

[dalai]

ok thanks again, really useful discussion.

I though I could just unscrew the existing nuts on the isolation valve and tap, remove the old pipes and then simply screw on the flexi hose.

But sounds like I can do this at the tap end but at the isolation valve end I need to make sure I have a clean piece of tube sticking out (no burrs) so I can fit the compression fitting?

This is all starting to make sense, thank you very much.

 

[fluxeyfingers]

I though I could just unscrew the existing nuts on the isolation valve and tap, remove the old pipes and then simply screw on the flexi hose.

If you did that, you'd be putting the washer against the taper of the compression fitting, and it would likely leak eventually.

But sounds like I can do this at the tap end but at the isolation valve end I need to make sure I have a clean piece of tube sticking out (no burrs) so I can fit the compression fitting?

You've got it - for the sake of a few quid, it's probably best to buy a tube cutter ("pipeslice").

 

[dalai]

do they not make flexi hose that will screw on to both tap and isolation valve?

 

[fluxeyfingers]

The issue is that the compression joint on the iso valve will have a sharp edge where the taper for the olive is cut. So the washer is placed under too much load. I'd usually solve this problem by using a couple of spare (compression) radiator tails. But for the price of a couple of radiator valves you could buy a tube cutter. Probably the cheapest type is known as a 'mini tube cutter', I usually only use those for 10mm but they will do for 15mm for a DIY job. But the pipeslice is a much easier tool to use.

 

[fluxeyfingers]

And yes, you can buy flexi's with a washer each end.

 

[dalai]

thanks again..

the existing copper pipe work from isolation valves is like this:

hot: 15mm tube up to tap

cold: 15mm tube slopes down into a 22mm tube upwards into a small 15mm length at the tap.

is this to avoid back-flow possibility from mains cold into the hot water or do I not worry about this with a combi?

may be this pipework was installed before the combi?

 

[fluxeyfingers]

Likely the 22mm is a hangover from a previous vented system. It's nothing to do with backflow and the 22mm can be safely removed if necessary.

Just to clarify: it's difficult to tell by the pic but I think you have (unusally) 1/2 inch bath taps and if so, the link I gave you earlier would be incorrect, and you would need http://www.screwfix.com/p/wras-push-fit-flexible-hose-500-x-15mm-x-1-2/37281 so best check the size of the tap tails (and associated nuts)

 

[dalai]

I think the taps are 3/4"?

the back nuts on the new mixer are about 31mm across flats.

 

[fluxeyfingers]

Aha yes, I forgot you were changing the tap. That is indeed 3/4".

 

[dalai]

so do you think I should go with a screw fix flexi hose with a 15mm compression fitting on one end and a ¾” BSP female thread on the other or something that will connect straight to the isolator valve?