Compression Fittings and Plastic Pipe

[TheScullster]

Hi all

Well, I re-worked the heating feeds in the kitchen ready for a kick space heater over the weekend. So now I have 2 pegler ball valves terminating my copper pipe feeds. After reading recommendations on the web, I tightened these onto the copper pipe a bit more than perhaps I have in the past (almost managed a complete turn beyond hand tight). As these are to be under kitchen units with close to zero access, future leaks are not an option.

From the other side of my ball valves I am considering running plastic pipe. All it will need is a short straight, an elbow and a longer straight (300mm maybe). At this point it will connect to the flexibles for the kick space heater - again metal compression fittings onto plastic pipe. So, two compression fittings and two push fit joints (each side of elbow) for each of two short pipes. Whilst I have used small amounts of plasic before, I want to be sure of these joints. Yes, I have the plastic pipe cutters and know about the pipe end inserts.

The question more relates to the compression connections and how tight to make these. Having done numerous copper joints, I've got a reasonable "feel" for these. With plastic, how tight (number of turns) is usual to guarantee a good join without crushing the pipe? Also, is any additional jointing material recommended (PTFE on olive etc)?

TIA

Phil

[Dave Liquorice]

Can't you just fit longer flexibles direct to the heater from your valves? Eliminates four joints (two for the elbow and two at the pipeflexy). You might have trouble sourcing long (500 or 600mm) ones depending on what connector is required at the kick space heater end.

[dom]

Long flexibles sounds like good advice. But if you do use plastic pipe into compression fittings - it's easy. Probably more forgiving than compression onto copper. I first tighten until the joint is stiff and the pipe can't be twisted in the compression fitting, then as I tighten a little further, I can feel it biting into the plastic a bit

- there I stop.

As anything, have a practice with a free bit of old plastic pipe, an old compression fitting and a new olive. Take it apart and check the olive has bitten firmly into the plastic, but not to the extent of compromising the pipe (I think you'd really have to do a job on it, to do that anyway).

[TheScullster]

Hi Dave

The orientation of my valves means I have to elbow 90 degrees before the flex connections. This is so that the flexibles initially run parallel to the wall behind the heater, then themselves bend 90 degrees to the heater connections IYSWIM. All based on Myson's recommended piping layout - the Myson units being supplied with 750mm flexis with integral ball valves.

Phil

[TheScullster]

Long flexibles sounds like good advice. But if you do use plastic pipe into compression fittings - it's easy. Probably more forgiving than compression onto copper. I first tighten until the joint is stiff and the pipe can't be twisted in the compression fitting, then as I tighten a little further, I can feel it biting into the plastic a bit

- there I stop.

As anything, have a practice with a free bit of old plastic pipe, an old compression fitting and a new olive. Take it apart and check the olive has bitten firmly into the plastic, but not to the extent of compromising the pipe (I think you'd really have to do a job on it, to do that anyway).

Thanks Dom

Good idea about doing trials - obvious really except I hadn't thought of it! I have checked the Hep20 instructions on this, but they don't specify number of turns. Also, they say PTFE tape may be used "if lubrication is required" - but don't indicate where lubrication would be required.

Phil

[<me9]

I changed a kickspace heater a couple of years ago, the original was plumbed in in copper, and the new one had flexibles. After about 18 months, when re-balancing the system, the (built in and unservicable) ball valve failed on the flexible. The flexibles were about 900mm IIRC. I couldn't get a suitable replacement in a hurry (Temperature rating) and ended up replacing it with a length of plastic pipe, which is flexible enough to allow removal for servicing.

[TheScullster]

wrote

Did this involve making/dismantling any compression joints *under* kitchen cupboards? This looks like a tricky operation, once units are in place. With only 150mm of clearance, that looks like a real PITA.

Phil

[dom]

Yup, important point - many flexies aren't rated for *continuous* use at temperature.

[<me9]

Slight PITA. The original heater was fitted after the units, and the pipes routed in 50mm holes near the front of the underunit space. It would have been a whole lot worse if the pipes had been routed at the rear.

The plastic pipe I routed as a long loop through a hole at the back of the units into the next (1000mm) space where the heater was. This gave just enough flexibility to be able to pull unit forward for servicing. THe original hard wired unit had been scrrewed to the floor making any work on it a PITA. It happened to fail (conveniently!!!) on christmas eve when we had visitors. Surprisingly we managed to source the new one locally that day.

[TheScullster]

wrote

My FIL has an old heater which likewise is screwed down. The downloaded installation manual for the new units suggest that they are free standing - is that right?

Phil

[John Rumm]

Same as any compression fitting really - a bit of PTFE on the threads will no nothing for soundness of the joint itself, but it does make the nut smoother and easier to tighten.

[TheScullster]

"John Rumm" wrote

Hi John

In this case, the PTFE is shown applied around the olive. I spoke to Hepworth Technical this morning and queried the use of PTFE with them. Their response was not wholly convincing - the guy I spoke to had to go and consult with a colleague. He then came back and declared that although it is optional, the use of PTFE in this way is considered best practice.

Phil

[The Medway Handyman]

Toolstation do them 900mm long for £3 -£4.

[John Rumm]

Yup, PTFE on the olive is quite different. On copper - its something that generally speaking you are not supposed to do and ought not be required. However it can help on the odd occasion where you can't get a reliable metal to metal seal. (probably when there is a fine scratch causing a slow weep).

On plastic, be guided by the makers advice I suppose. Personally I have never used it on olives on plastic pipe, and have never had difficulty getting a seal.