PTFE tape on fuel fittings

Malish

Malish

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I'm replacing a diesel fuel line which has corroded. The outlet from the tank looks like a 1/4" tapered BSP male thread onto which I intend to attach a straight 1/4" BSP female. If it were an air line I would use a length of PTFE tape to ensure the thread seal - in this case I was wondering if the PTFE will be affected / dissolved by the diesel?
 
I would use PTFE tape but let's wait for someone to say not to.

It's important to ensure that no strands of PTFE protrude into the fuel stream as you can get intermittent blockages
 
It won't be dissolved by the diesel (at least it wasn't on my pipes) the only danger I've heard of is if you get any scrap or wisp in the pipe, where it might detach and become a blockage further downstream.
 
I wouldn't have thought PTFE going astray is much of a problem as It will always be used on fittings between the tank and the engine.

ie: there will be a filter in the way to catch the bits if any. Fuel fittings on the engine normally use copper washers or flare fittings which don't need any extra sealant.
 
FWIW we had an embarassing engine breakdown once because a tiny bit of PTFE tape, presumably from the joint on the outlet of the primary filter, jammed open the non-return-valve in the pump, rendering it useless.
 
I think you will find proper red jointing compound is the stuff Do not think central heating engineers use it on oil lines -but you could pop in to a heating spares wholesaler and ask
 
Not really a good idea to use PTFE for reasons others have said. We use a jointing compound specifically made for diesel lines. It's usually available at places selling diesel spares and accessories for lorries, I also found it once in Halfords. It sets enough to stop leaks but doesn't glue the parts together - very effective.
 
Nothing wrong with PTFE, it is resistant to diesel and forms a good seal. Bits don't get in the line if its applied properly.

Wound round male thread in direction of thread i.e clockwise when viewed from end. 1st 1 to 2 threads should be left uncovered then it doesn't end up in bore of pipe. 3 to 4 turns should be satisfactory.

Regards

Steve
 
Yes .... but in moderation ....

Some people have the idea to wind on loads .... I have an inspector who does on our additive injection gear .... such that later when we undo the coupling ... and want to redo it - it leaks where he's forced the joint with layers of tape.

PTFE tape is designed to sit IN the troughs of thread and provide sealing .... not as he does ... put stress on the fitting !!
 
ptfe can indeed be affected by the diesel. You are much better using loctite lockseal. I had problems of air for a long time until I removed the ptfe and used the lockseal.
 
On an earlier PTFE tape thread , I didn’t get much support for my opinion that the prime purpose of PTFE tape was to lubricate the thread and not to seal it.

I agree with Michael-w’s post which also reinforces my view. The sealing component of joints has little to do with the thread of the fixing. There is always something else which provides the seal whether it is a flared end, an olive, a copper washer or other item. The thread is just a mechanism for tightening the joint. There are plenty of examples where seals are achieved without any threaded component (as in the spring clip mechanism of a Kilner jar) or where the thread is external to the joint (some exhaust manifolds are like this and use a bridging bar to apply the force).

If liquids or gases reach the thread, then the joint has already failed and cannot be relied on. The PTFE tape reduces the friction of the threaded components allowing a much better application of the tightening forces although I accept that it will have some secondary sealing properties.

Teflon® is the registered trademark of PTFE (polytetrafluoroethylene).
 
[ QUOTE ]
The sealing component of joints has little to do with the thread of the fixing.

[/ QUOTE ]While this is true for compression joints and tap connectors and such I'm fairly sure that it's not true for tapered thread type joints where the thread is cut with a taper so that it seals at some point when tightened up.
 
I used Gas seal, i wont use ptfe, scared bits will break of.
Gas seal is fine with LPG, and is used by Volvo.
Not to sure if gas seal is the brand name but it comes in a red box, and is a white/off white colour
 
just a quick one:

Dont use 'Red Hermatite' with or without PTFE tape as diesel washes it away.

i agree with above about the fact that PTFE is only a thread lubricant and not a sealent and would advise against the use on fuel systems, but eh thats just me. I always use Loctite 756 i think it is for sealing diesel. its worked for me for over 18 years, so ill keep using it.
 
I disagree with above about the fact that PTFE is only a thread lubricant and not a sealant, but eh thats just me. I always use PTFE tape on gas and fuel connections. It's worked for me for over 30 years, so I'll keep using it. /forums/images/graemlins/grin.gif
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For ref: I sourced some Hylomar 5059 liquid thread sealant from ASAP Supplies fuel resistant & void filling. If there are no more messages from me on this thread then assume it has worked a treat.
 
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