PTFE tape & fluid for fuel line threads?

[blackrose]

I read this on the RS website and assumed that if PTFE tape is ok for sealing threads on diesel lines then PTFE fluid will be better as it eliminates the possiblity of shards of tape breaking off and ending up inside the fuel line.

PTFE Tape for Petrol and Oil

Due to its chemical inertness, PTFE tape is resistant to both petrol and oil. Therefore, it is often used in automotive applications to seal and lubricate fuel line joints.

 

I happen to have a bottle of this stuff so would it be ok? I don't want to buy Hylomar Blue if the stuff I've got is suitable.

 

https://shop.vitcas.com/ptfe-liquid-anaerobic-pipe-thread-sealant.html

 

[dmr]

Can't give a direct answer.

As you know most fittings seal on an olive, seat, or face and washer, so its only really BSP tapers where a sealant is required. Heldite is often mentioned for sealing fuel connections, I have tried it, it can be a bit messy, but it works.

[blackrose]

I'm trying to seal parallel UNF threads.

[Jen-in-Wellies]

19 minutes ago, blackrose said:

I'm trying to seal parallel UNF threads.

Is using a copper washer possible?

[dmr]

18 minutes ago, blackrose said:

I'm trying to seal parallel UNF threads.

 

That's high risk. I think I would use a Lot of PTFE tape but put it on with care so that none can protrude out into the fuel passage. Is there any sort of half decent face involved so you could use a flange head bolt and a copper washer?

[blackrose]

31 minutes ago, Jen-in-Wellies said:

Is using a copper washer possible?

 

I'm going to use copper sealing washers but wanted a sealant between male & female threads.

 

30 minutes ago, dmr said:

 

That's high risk. I think I would use a Lot of PTFE tape but put it on with care so that none can protrude out into the fuel passage. Is there any sort of half decent face involved so you could use a flange head bolt and a copper washer?

 

With the two parallel UNF threaded joints I can use copper washers, but here's one other joint without the possibility of using a washer, but that's a different tapered thread so I should be ok.

Edited September 5, 2021 by blackrose

[GUMPY]

Heldtite is the best for sealing threads in diesel lines, its what it was made to do.

https://www.rustins.ltd/heldite/our-products/heldite-jointing-compound
the wrong type of PTFE tape will disolve in fuel creating a sludge

Edited September 5, 2021 by Loddon

[blackrose]

Ok thanks All.

[BEngo]

Screwfix sell a pipe thread sealant.  It is pale blue.  It is what I used to seal the UNF threads for a Delphi 296 filter. It is at home  so I can't check for the exact name now.

 

N

[Guest]

35 minutes ago, BEngo said:

Screwfix sell a pipe thread sealant.  It is pale blue.  It is what I used to seal the UNF threads for a Delphi 296 filter. It is at home  so I can't check for the exact name now.

 

N

 

https://www.screwfix.com/p/fernox-ls-x-leak-sealer-50ml/23614

 

This?

[BEngo]

No.  LS1 is a silicone based clear substance.  The pipe sealant is pale blue and quite runny.  it is called tru blu pipe thread sealant:  item 40236. £3.44

 

N

[DHutch]

Two things come to mind with this.

 

 1) PTFE might be fuel safe, but liquid sealant containing PTFE is something completely different.

 2) It is, broadly speaking, not advisable or sound engineering to try and generate a seal on parallel threads.

 

 

 

The parallel threaded fittings should have a flat, machined, sealing face on to which a soft copper washer can be used to form a seal. At which point I would ensure all is clean, use new washers, and no PTFE or liquid sealant. Correctly assembled there should be no leaks.

 

 

Fittings where there is a tapered thread, ideally both sides tapered as per threaded pipe fittings, then usually I would use PTFE, winding it on the correct way so it is tightened when the fittings are put together, and carefully not going over the end of the thread, typically starting around one thread from the end, and I understand PTFE should be safe for diesel, petrol, and even ethanol. However I am not overly experienced with diesel fittings, have not usually see tapered fittings used on modern fuel systems, and have also heard good things about Heldtite on other forums as well as previously on this one. Tapered fittings where only side is tapered (typically the male side) will also usually work ok.

 

Olives based compression fittings are again an all metal soft/copper based sealing system, and should seal perfectly first time without any sealant tape or fluid. Certainly putting PTFE on the threads of a compression fitting is a false action. Yes sometimes there are times where you are assembling a compression fitting, which has been apart many times, and has suffered damage or otherwise become problematic, and replacing the olive and or remaking the connection with fresh pipe isnt practical, at which point a turn of tape or a blob of the right grade of liquid sealant can get you out of a hole, we've all done it. But its not right and shouldnt really have a place on a boat fuel system.

 

 

Daniel