Pipe sizing for LPG Hob

[JanetE]

Can't be sure I have put this in the correct section.

We are not having gas but we are having a two ring LPG gas hob in the kitchen just as a standby.  We have to make the hole through the timber frame so we can fit the pipe through into the kitchen. The gas bottles will sit outside in a secure box.  We just need to ensure we make the correct sized hole and wonder if anyone can help?  I think these are run off flexible rubber pipe, which is sheathed for protection.

Thanks.,

[ProDave]

You can't have flexible pipe indoors, that is just for the connection to the bottles outside.

Our 5 burner hob runs fine from a 15 metre long run of 10mm copper pipe.

The normal arrangement is a 2 bottle automatic changeover regulator. So HIGH pressure hoses from each cylinder to the regulator and copper from the regulator to the hob.

Don't forget presure test points etc.

Inside there is a bayonet fitting for the the cooker hose to plug into, that's the only bit of flexi pipe you would normally have indoors. In the case iof a fixed hob you probably wouldn't have that and a direct connection of the copper pipe to the hob.

[dimpsy]

I saw an ad in a magazine for something called flexigas, semi-rigid stainless steel flexible gas pipe tubing,should do the job I think,but I'm no plumber.

[TerryE]

Dave, in many ways using copper is actually easier because the installation within the building fabric is robust and rigid.  I've done gas plumbing before, but that was in the days before you had to go on a long course and get a certificate to prove that you understand that you can't use flux and have to pressure test everything as part of commissioning.   I've still got the clear plastic tube to use as a manometer, but it would some new red wine to colour the water.

Our primary hob is induction, and as Jan says these two rings are purely backup so that we aren't totally stuffed in a power cut, so we'll probably keep it simple and use a single bottle.

[ProDave]

It used to be acceptable on LPG to use compression fittings, something that seems to be frowned on for mains gas. Is that still allowed?

[Nickfromwales]

No compression on gas. 

Your ok with control valves etc, and a temp cap end for testing, but soldered joints everywhere else.

@TerryE , what do you mean by no flux?

[TerryE]

An old gas fitter showed me how he did it about 20 years ago.  The then BGas rules were that you weren't allowed to use flux when doing end-feed joints.  I guess the logic was that unlike wet work, any residual solder in the pipes wouldn't be flushed and therefore slowly corrode the pipe internals and if carried into the appliance that as well.  He burnish his pipes till they were oxide free and brilliant, then tinned the pipe and burnished both the fitting and the pipe again, before soldering with a flux-free solder.  My hit rate using a flux-free  solder is a lot worse than with, so I would prefer the options of flushing the assemble piece with water then air to remove any internal flux.  Of course you'd need to let the pipe fully dry before doing a manometer test.

[Temp]

4 hours ago, JanetE said:

We are not having gas but we are having a two ring LPG gas hob in the kitchen just as a standby.  

No mains gas in our village but because we like gas hobs we installed a dual fuel electric oven and LPG hob with 6 rings. Works very well off LPG cylinders. We use 47kg cylinders but they last around 18 months to 2 years so smaller cylinders would be ok and easer to transport.

We used plastic covered copper pipe sold for the purpose.

[Nickfromwales]

51 minutes ago, TerryE said:

An old gas fitter showed me how he did it about 20 years ago.  The then BGas rules were that you weren't allowed to use flux when doing end-feed joints.  I guess the logic was that unlike wet work, any residual solder in the pipes wouldn't be flushed and therefore slowly corrode the pipe internals and if carried into the appliance that as well.  He burnish his pipes till they were oxide free and brilliant, then tinned the pipe and burnished both the fitting and the pipe again, before soldering with a flux-free solder.  My hit rate using a flux-free  solder is a lot worse than with, so I would prefer the options of flushing the assemble piece with water then air to remove any internal flux.  Of course you'd need to let the pipe fully dry before doing a manometer test.

I don't use strong acidic ( self cleaning ) flux, such as Laco, as I see it as the choice of the lazy man. It's only really with fluxes like that that you get the problematic residues. I use Telux ( mild ) flux as a rule, which requires you to mechanically clean the metals first ( using wire wool / abrasive pad / emery cloth etc ), and gives far better results in my experience, ( and I've soldered many thousands of joints ). 

For gas pipework I'd really not be worried about residual flux making it through to the hob, and with Telux, I'd certainly not ever be worried about the flux corroding the pipe. When I'm soldering with mild flux the flux almost evaporates off the fitting, with very little residue left behind, but when I have to use Laco / Powerflux I notice a lot of the flux doesn't flow away or evaporate like it does with mild. On that basis is say your mates 'burn, clean, tin and bond method would have merit, just a lot of work when it's easier to clean once, solder with mild flux and get as good, if not better, results.  Purging the pipework with water at cold mains pressure may dislodge any residual residue, but as the gas will only ever be walking down the pipe, it's a pointless endeavour IMHO, plus I'd never recommend purposely introducing water to a gas line, and trying to dry out a 10 or 15m long run, in situ, would be less than easy   

[PeterW]

10 hours ago, Nickfromwales said:

I don't use strong acidic ( self cleaning ) flux, such as Laco, as I see it as the choice of the lazy man. It's only really with fluxes like that that you get the problematic residues. I use Telux ( mild ) flux as a rule, which requires you to mechanically clean the metals first ( using wire wool / abrasive pad / emery cloth etc ), and gives far better results in my experience, ( and I've soldered many thousands of joints ). 

 

I've noticed that the trend is to teach that the flux does the job rather than the elbow grease which always surprises me. I "inherited" my dads old Laco tin which I only threw out and replaced with a new tin because it corroded..! That must have been 20 odd years old and still half full as I was taught you needed to clean first and then the flux was just enough to clean and allow the solder to flow. 

Saying that, I saw one of the lads I know (BG apprentice) do some lovely solder work that was all end feed and it was very neat but they have been banned from doing any hot work in lofts so he's now saying they are doing more and more with Hep2O.

Another skill being lost ..... 

 

 

[Jeremy Harris]

I always thought that the flux free copper jointing done on gas and refrigerant pipe was done with the low temperature fluxless copper alloy brazing rod.  I still have some, but haven't used it in years.  It needs a nice clean joint, but used to be relatively easy to use, although needs a lot of heat.

Modern solder flux is tallow based, as far as i can tell, and has no cleaning power at all, it's simply an anti-oxidant (some may recall using grease or oil fluxes in the past that worked the same way).  There were a couple of "cleaning fluxes" in common use, my preference was to use zinc chloride, either in the liquid form (Bakers Fluid) or as a paste where it's mixed with grease.  Both leave residues and are now listed as unsuitable for potable water, I believe (along with tin lead solder). 

The tin lead solder ban is a pain, as the non-lead solder isn't syntectic, so can crystallise and go brittle if there is even the tiniest bit of movement before it's fully solidified.  It doesn't seem to flow as easily into end feed fittings, either.  The irritating thing is that the decision to ban it wasn't based on any credible risk from lead leaching from soldered pipe joints, especially given the very tiny area of solder exposed to water in any properly made joint.  The ban is part of a very much wider ban to remove lead from all products, whether it's harmful in that application or not.

[Nickfromwales]

I'd have to disagree about modern mild fluxes not cleaning. It's immediately apparent when the flux is introduced that there is a cleaning quality to it ( telux in my instance ). 

I clean the copper / brass with emery or wire wool, depending upon grottiness, and apply a thin layer of flux to both mating surfaces. I also lightly coat the first 2-3 " of the lead free solder so as to keep fluxing the joint as I go, rather than stopping to dip the solder in the flux ( which it then doesn't want to take to as the solder is hot and the flux just drips / fall straight off ). After initially soldering a joint and the flux has 'evaporated', I run the flux brush over the joint to brighten it back up and to flick the snot of solder off the lowest part of the joint ( where it collects as a drip ) to neaten things up. 

The mild flux definitely cleans, of this I'm 100% sure.

Fluxless soldering of refrigerant pipe work or very large bore water pipe work is brazing, not soldering, so a totally different discipline imho. I very much doubt the filler material ( brazing 'solder' ) carries through the entire joint depth, like solder does with capillary action ). That's more a weld which is visible vs a soldered joint which can be near 100% saturated but with almost no visible solder on show ( if your neat, and don't overheat the joint during soldering ). 

BGas guys don't do the best of jobs tbh, and I've been behind a good few cleaning up after them as they refuse to do so as long as it's 'working'. I had one such call out where I contacted BG and told them if they weren't back there within the hour to correct a new £5k heat-only boiler install ( £5k for a £700 glow worm boiler, soooooo cheap  ) that I was going to report them to the GSR and Riddor their asses.

They said no, so I emailed them photos of the job and said I was going to email them accordingly next if there's no response. They were there 45 mins later rectifying the faults as it was lethal.  That was an elderly couple 82 and 83 years old. ?

[Jeremy Harris]

I didn't mean non-cleaning in terms of not removing copper oxide (the dull colour of copper) they do that by being an anti-oxidant.  I meant non-cleaning in terms of not being able to remove contaminants from the pipe, dirt, paint, burned flux etc.

The copper alloy fluxless brazing rod I have penetrates pretty well, not as well as solder, but it does get sucked into the joint as long as it is spotlessly clean.

I've just been out and checked, and it's a copper/phosphorus alloy, marked CuP6 on the packet.

[Nickfromwales]

10/4. 

Just haven't yet met anyone who'd not remove paint etc from a surface, mechanically, before fine cleaning and prepping with flux so didn't even enter my head tbh.

The Laco certainly has its place in my van, as on old 3/4 stuff or 1" stuff it's usually quite deeply pitted too so you need s chemical clean to get into the grain of the surface. Laco cleans so well you can actually see it happening, but I always use that as a preparation and clean it all off before final assembly. If I'm really paranoid, I'll coat the first inch or so of the solder in Laco and solder the 'old' end first, and resolder it again last with mild and fresh 'mild coated' solder. 

I suppose it's easy enough to braze smaller bore stuff with greater suction than it is with big stuff ( 54mm and up ) as its harder to apply heat evenly. 

[Jeremy Harris]

The La-Co stuff uses ammonium chloride and ethanalomine hydrochloride as cleaning agents rather than zinc chloride, I believe, so is nearly as aggressive at cleaning copper as the older stuff like Bakers Fluid (still my favourite!).  The paste also uses a non-grease stiffening agent (not 100% sure, but I think it may be PEG based) so doesn't leave a toxic, burned on, residue.

[Nickfromwales]

That was my next question . 

Thanks. 

[Jeremy Harris]

I have to say that I'm a great fan of zinc chloride based solder fluxes and proper 60/40 tin lead solder.  It might not be "legal" for use on copper water pipes any more, but it is a heck of a lot easier to use and, for an amateur with limited soldering experience, far less likely to result in a bad joint.

For similar reasons I still always use 60/40 tin lead solder and rosin-based flux for electrical work.  Not only are the joints easier, but they are far more reliable.  Modern electronic equipment failure is, in my experience, likely to be caused by the failure of a lead-free solder joint.  Lead-free solder is more brittle, and as above, being non-syntectic it is extremely sensitive to slight movement as it cools, leading to crystallised joints that are prone to early failure.

Yes, lead poses a risk, but the regulators have got the risk to the end users completely out of proportion, as any bit of reasonably conducted science will show.  The real lead risk is in mass production, where lead vapour is expensive to eradicate from the atmosphere, not someone making a few soldered joints.

[Nickfromwales]

Yup, I still carry 'true leaded' solder on the van for sweating copper to lead etc, or for flooding old joints in situ ( where cutting out and replacing a leaking joint is not possible / cost / damage effective ). With that stuff I can literally form a 'belt' around a fitting, therefore bridging the leaking part of a poorly soldered / dry, and subsequently leaking, joint. A skill not many new plastic-heroes posses 

 

[Jeremy Harris]

Out of interest, is your view of lead-free solder similar to mine?  I find the stuff a real pain, compared with the ease of using tin/lead.

[Nickfromwales]

In part, yes. 

I do prefer the 'runny-ness' of the unleaded solder but it took a while to become a fan, due to me using leaded for so long prior to 'the change'. I do like the way that UL'd solder stays bright on the coil, where as L'd solder tends to go black and dirty, and then that gets deposited on the joint as it's going. 

I've always observed a 'no bump / knock' policy whilst my soldered joints cool down. I use a cold wet rag to instantly cool my joints which pretty much guarantees that I don't get brittle joints, and what you say about UL'd there is 100% spot on. Not many people know about it or actively prevent disturbance during cooling, particularly DIY'ers. 

[Jcplumb]

Can use compression joints on gas as long as it's accessible. Never use water to test gas pipe. use air.  

[Nickfromwales]

2 hours ago, Jcplumb said:

Can use compression joints on gas as long as it's accessible. Never use water to test gas pipe. use air.  

Should also read “visible” as compression on gas is less than preferable.