Compression joints and tapoured male /parrallel female joints

[VicS]

Although it is used to seal, I was under the impression the primary function of PTFE tape was as a lubricant.

That can't be the primary function with tapered fittings. If you put oil, silicone or graphite lubricant on a tapered fluid or gas joint I'm 100% sure that it will still leak.

Richard

AFAIK the primary purpose is to seal joints where the seal has to be made between the threads, in place of traditional materials such as hemp.

There is clue in the fact that it is often called "threadseal tape".

BTW there are several colour coded grades of this stuff for different purposes/ thread sizes

 

[vyv_cox]

There is a useful page on making up compression fittings here http://www.plumbteamltd.co.uk/compression.html It says of PTFE tape that it can be used in emergency, for leaking joints, but can be problematic. This of course is for domestic water systems.

So far as fuel systems are concerned PTFE should never be used, either on gas or liquids. The orifices in injectors, burners and diesel pumps are small and can easily be blocked by 'fibres' of PTFE. One of the examples I give on a failure diagnosis course is that of a 60 MW gas turbine that was burned very badly, losing a complete combustor can when a fragment of PTFE tape partially blocked a nozzle, diverting the flame path onto the liner. That failure cost over $2,000,000 to repair.

This site http://www.thomson-caravans.co.uk/advice/diyprojects/gascompressionfitting.htm also condemns pastes and sealants, for good reason.

 

[saltyrob]

Hi Folks,

Sorry for not replying earlier, work prevented.The back ground to my post is that I am having to connect a cooker with an 8 mm tail to the existing 3/8 copper supply via a new 3/8 stainless steel braided encased hose. I have spoken to the tech departments for several specialist plumbing suppliers and the solution was a fitting incorporating an 8mm compression joint and 1/4 tapoured male thread joined to another fitting incorporating a 3/8 compression joint and 1/4 parallel female thread. I have not been able to find another solution and information on the net seemed to imply that a tapoured male fitted to parallel female was satisfactory. I am a very careful when carrying out any work on the boat, prefer to ask and appreciate your advise

Many thanks again

Rob

 

[Seajet]

The thing I'd like people to understand is this.

For aviation ' pipework ', ( which incidentally I was initially trained on ) usually things like stainless small diameter pipes and components carrying high pressure hydraulic fluid etc, one would never dream in a million years of using things like PTFE.

The pipes and components are high quality, manufactured to high tolerances and well treated in storage and transit.

Domestic plumbing is I am afraid another world !

The tolerances are at best slapdash, and would make an aviation designer spin; that's even from the same supplier.

Storage and transit methods are brutal.

So plumbers coping with this have learned that for low pressure ( but inc water mains ) systems, PTFE does indeed help a lot with taking up the ' slackalarity ' of the pipes and components.

This isn't just restricted to Chinese stuff I'm afraid, a certain famous old British manufacturer of sanitary ware seems to have quality control performed by a group of dedicated technicians, when not at their day job in the Big Top tent...

 

[VicS]

Hi Folks,

Sorry for not replying earlier, work prevented.The back ground to my post is that I am having to connect a cooker with an 8 mm tail to the existing 3/8 copper supply via a new 3/8 stainless steel braided encased hose. I have spoken to the tech departments for several specialist plumbing suppliers and the solution was a fitting incorporating an 8mm compression joint and 1/4 tapoured male thread joined to another fitting incorporating a 3/8 compression joint and 1/4 parallel female thread. I have not been able to find another solution and information on the net seemed to imply that a tapoured male fitted to parallel female was satisfactory. I am a very careful when carrying out any work on the boat, prefer to ask and appreciate your advise

Many thanks again

Rob

So 8 mm compression one end
3/8" compression at the other

Thats fine. No tape no jointing compound. No ifs or buts about it on LPG, but be sure to use soft copper olives , not brass ones

1/4" tapered male to 1/4" parallel female in the middle.
Not ideal but its commonly done. You will need tape on that. Use the yellow stuff for gas.
Wind it on to the male thread in the same direction that the female will screw on. Not too much. You need to be sure that the threads are engaging and not just screwing onto ptfe tape. You only need enough to seal the gaps between the threads.

Alternatively a sealing compond such as Rocol Gas Seal http://www.gasproducts.co.uk/acatalog/Rocol_Gas_Sealant_300gm.html

 

[sailorman]

So 8 mm compression one end
3/8" compression at the other

Thats fine. No tape no jointing compound. No ifs or buts about it on LPG, but be sure to use soft copper olives , not brass ones

1/4" tapered male to 1/4" parallel female in the middle.
Not ideal but its commonly done. You will need tape on that. Use the yellow stuff for gas.
Wind it on to the male thread in the same direction that the female will screw on. Not too much. You need to be sure that the threads are engaging and not just screwing onto ptfe tape. You only need enough to seal the gaps between the threads.

And dont over tighten & split the nut :encouragement:

 

[Seajet]

You winge about PTFE then think a tapered male fitting into a parallel female is OK with GAS and a presumably gymballed cooker ?!!!

I really hope I have misunderstood Saltyrob's description; if I haven't and you have a setup like this, please just fly Flag ' B ' and keep well clear...

 

[VicS]

You winge about PTFE then think a tapered male fitting into a parallel female is OK with GAS and a presumably gymballed cooker ?!!!

I really hope I have misunderstood Saltyrob's description; if I haven't and you have a setup like this, please just fly Flag ' B ' and keep well clear...

Not ideal...


please post links to the fittings necessary to make an A1 job of this..........preferably a straightforward 8mm to 3/8" compression union .

 

[Seajet]

As you have done nothing but scoff and make out you're such a genius, surely you have all this available as holograms from your magic ' was chemist but now master of the universe ' arse...

 

[David2452]

Hi Folks,

Sorry for not replying earlier, work prevented.The back ground to my post is that I am having to connect a cooker with an 8 mm tail to the existing 3/8 copper supply via a new 3/8 stainless steel braided encased hose. I have spoken to the tech departments for several specialist plumbing suppliers and the solution was a fitting incorporating an 8mm compression joint and 1/4 tapoured male thread joined to another fitting incorporating a 3/8 compression joint and 1/4 parallel female thread. I have not been able to find another solution and information on the net seemed to imply that a tapoured male fitted to parallel female was satisfactory. I am a very careful when carrying out any work on the boat, prefer to ask and appreciate your advise

Many thanks again

Rob

In that case a little Clessetite LPG compression joint sealant will not come amiss, though I don't use it as a sealant per se it is useful to lubricate threads in difficult areas (e,g. a boat) and give consistent joints. I use it on compression joints from 4mm to 8mm (My earlier advice was for plumbing of 15mm +) as a matter of course just to make life easy, it also aids the olive spreading by giving a little lubrication, not unlike a little grease allowing a head gasket to spread during tightening, I make many joints per week and don't have leaks. For joints of jour size then I suggest you insist on soft copper olives.

 

[saltyrob]

Hi Folks,

This must be a common issue where a new cooker is fitted in an older boat with different pipe sizes so I open to any ideas on how it can be achieved. I have not been able to source a reducing compression joint to fit both 3/8 and 8 mm .

I should have been clearer in my original thread and that may have avoided any misunderstanding

Rob

 

[David2452]

Hi Folks,

This must be a common issue where a new cooker is fitted in an older boat with different pipe sizes so I open to any ideas on how it can be achieved. I have not been able to source a reducing compression joint to fit both 3/8 and 8 mm .

I should have been clearer in my original thread and that may have avoided any misunderstanding

Rob

3/8" BSPF to 3/8" compression and 3/8 BSPM to 8mm compression is what I use. Never been able to find a 3/8" to 8mm compression fitting

 

[VicS]

3/8" BSPF to 3/8" compression and 3/8 BSPM to 8mm compression is what I use. Never been able to find a 3/8" to 8mm compression fitting

Thats the answer.Even 1/4 BSP would be ok I think, but where does he find the compression to BSPM fittings ... every where Ive looked I found only tapered male fittings.

what would you think of hard soldering the parallel and tapered fittings together ?

 

[David2452]

what would you think of hard soldering the parallel and tapered fittings together ?

Same as I think about soldering anything on a boat, tube, conductors, whatever, i don't like it. BSPPM to mm compression are readily available from the likes of ASAP but I buy from BES, part #s for the pair are 17623 & 9477 for the combination I mentioned.

 

[VicS]

Same as I think about soldering anything on a boat, tube, conductors, whatever, i don't like it. BSPPM to mm compression are readily available from the likes of ASAP but I buy from BES, part #s for the pair are 17623 & 9477 for the combination I mentioned.

I had not found them on ASAP or BES websites but now the OP has the part numbers that all solved


I was not suggesting soft soldering BTW.

 

[cliff]

FFS take a 8mm compression fitting and open one end to 3/8" and fit a 3/8" olive. All one needs is a lathe, a countersink, a 3/8" drill bit and a spare 3/8" olive.
Job done in one fitting. I have made a number of these over the years for myself and others and no problems.

 

[NorthUp]

FFS take a 8mm compression fitting and open one end to 3/8" and fit a 3/8" olive. All one needs is a lathe, a countersink, a 3/8" drill bit and a spare 3/8" olive.
Job done in one fitting. i have make a number of these over the years for myself and others and no problems.

Sorry, but the boat's insurance will become invalid if you did that...

 

[VicS]

FFS take a 8mm compression fitting and open one end to 3/8" and fit a 3/8" olive. All one needs is a lathe, a countersink, a 3/8" drill bit and a spare 3/8" olive.
Job done in one fitting. i have make a number of these over the years for myself and others and no problems.

"All one needs is a lathe" ... and every one has one of those lying around?


Oh yes, I'd forgotten about that

 

[NorthUp]

I used to do cliff's mod with a pillar drill, square up the fitting with a small drill through the centre, secure in vice, drill as required.

 

[cliff]

I used to do cliff's mod with a pillar drill, square up the fitting with a small drill through the centre, secure in vice, drill as required.

A man after my own heart - improvise, don't bodge!