A few newbie plumbing questions

[Stu1H]

After years of avoiding doing my own plumbing I figured it's about time I gave it a go so a couple of questions.

First job it fit isolating valves to all my taps and toilets and renew my bathroom taps ....

1. Compression fittings / flexible hoses - are there any particular brands I should look out for or will the trade packs from Screwfix be decent enough?

2. Flexible hoses - just how flexible are these? On my bath taps there will be a distance of around 5" once the valve is fitted. Will 300mm be okay as I can only find push fit in 150mm.

3. Compression fittings - Am I better to use jointing compound or ptfe?

4. My cold taps are all mains fed so will use standard isolating valves. Assume it's best to use full bore valves for the hot taps? (Gravity/vented system).

5. The hot supply from my cylinder doesn't have an isolating valve. Would it be sensible to fit one whilst the tank is empty?

Thank you!

 

[oldbuffer]

1a. Compression fittings - generally much of a muchness but Conex / Pegler are better made. If joining to plastic pipes you'll need the correct inserts and copper olives. See also 4. below.
1b. Flexible hoses - use WRAS approved ones only. Be aware that the internal diameter of flexible hoses is much less than that of "equivalent" copper. Flexible hoses should not be joined directly to compression fittings (such as isolation valves) unless specifically designed to so connect.
2. Avoid radius of less than 120mm on 15mm hoses, or 200mm on 22mm hoses. No sharp bends. Re your specific bath, who can tell without knowing how the pipes run. Why not use a short piece of copper to bring the pipework to a position where 150mm is OK?
3. New compression fittings, particularly good quality ones, shouldn't need any jointing compound or PTFE. However, a bit of Jet Lube V2 either side of the olive is a bit of insurance. I wipe a bit onto the sealing faces of the fitting, and a bit (wiped round with a little finger) around the inside of the mating face of the nut. If you do use PTFE, do the fitting up to compress the olive, take it apart, three or four wraps of PTFE around the olive and reassemble.
4. Use only good quality isolating valves, e.g. Pegler. As you say, full bore for the tank fed outlets, and you can probably get away with ordinary ones for mains fed, although there's no harm in using full bore and might look better.
5. Isolating the cold supply to the hot water cylinder is enough to shut off the hot water (after a dribble from the pipes). Don't put an isolation valve on the hot water outlet unless you really know what you're doing and can avoid putting a valve in the vent run.

 

[PrenticeBoyofDerry]

1. Compression fittings / flexible hoses - are there any particular brands I should look out for or will the trade packs from Screwfix be decent enough?

You will find the trade rated items are good, but always worth looking on the reviews if you have doubts.

2. Flexible hoses - just how flexible are these? On my bath taps there will be a distance of around 5" once the valve is fitted. Will 300mm be okay as I can only find push fit in 150mm.

125mm is a bit tight for flexies, really want at least 250mm to play with, as you can reduce flow and damage the item, if forcing it into small areas.

3. Compression fittings - Am I better to use jointing compound or ptfe?

Really you should not need to use either on compression fittings, but either is fine in my opinion, there will be times where one is better than the other, but that is an assessment that is made at the time. So always have some of each.

4. My cold taps are all mains fed so will use standard isolating valves. Assume it's best to use full bore valves for the hot taps? (Gravity/vented system).

My opinion is full bore for both

5. The hot supply from my cylinder doesn't have an isolating valve. Would it be sensible to fit one whilst the tank is empty?

There should be an inline gate valve that feeds the cold water to the cylinder, that is where you would isolate the cylinder.

 

[Stu1H]

Thanks oldbuffer and PBoD for the advice.

With the bath taps, the feeds come through the wall at about 7-8" under the taps. Don't really want to get into rerouting the pipework at this stage as I'm just giving the bathroom a quick makeover and I'll be refitting it in 2 or 3 years after I've sorted my kitchen. Hopefully by then I'll have more confidence with the work too!

Would using 500mm hoses be an option so I can do a full 360 to keep the bend at a minimum. I know it's probably not ideal but hopefully good for a couple of years until I do a complete refit?

With regards point 5 I have a valve on the cold feed to the cylinder. If I shut that off will that create a vacuum so I can work on the hot pipes without emptying?

Cheers!

 

[Stu1H]

Ignore my last question ... I've just realised I'm being a dick

 

[oldbuffer]

1. Yes, you can use longer flexi's and loop them. Not ideal but should last you a few years.
2. The hot water flows into your system under pressure from the difference in heights between the bottom of the cold water storage cistern (normally in the loft) and each hot outlet. This is why you generally get better flow in downstairs hot taps than upstairs ones. The hot water flows out from the top of the hot water cylinder. Shutting off the cold inlet to the hot water cylinder removes the pressure, and without pressure there is no flow. It doesn't really create a vacuum, but the effect is the same.

 

[PrenticeBoyofDerry]

500mm flex, is a better idea, as the loop should not cause damage to the hose.
You could manipulate a short rigid length using some speed fit though.
Even using a speed fit service valve.

Closing the gate valve, will allow you to open the hot taps and drain a little water from them, as you need to cut into pipes or crack open nuts on the hot side, it will not create a vacuum, also you will have an open vent pipe which will not allow this.

I would suggest prior to doing the work on the hot side, that you do not heat the water via immersion and isolate the element.

 

[Stu1H]

Thanks gents. I realised shutting off the cold feed stops the pressure seconds after hitting 'post' ... told you I was a newb

Thanks again!