Fuel Pipe: Tapered Threads?

I don't think that you have a parallel female thread. The "T" in NPTF indicates taper.
They should fit OK IMO. An "F" ( fuel ) thread on the pipe as well would be best.
Just thought, 1/4" BSP is 19 tpi, V. close but not really compatible. Make sure it isn't that on the pipe.
 
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Identifying what you have is the hardest bit. I had the same problem connecting an oil pressure gauge to my Suzuki engine. Can you use the old unit to take to a factor and try threads 'till you find a good match. I found that a non-match would screw in about 1 1/2 turns before tightening up.
 
I didn't think I'd ever say or type this but..

Fantastic - a fuel pipe thread, about fuel pipe threads!

I have just returned from attempting to fit a racor 210T as a replacement for the incumbent weepy filter in place since I bought the boat.

I was going to use an 8mm compression fitting to connect to the pipe, but the pipe had a 'nipple' on it so I couldn't remove the existing nut and furthermore could not fit the olive!

So I just bodged - I used half of my fitting to connect to the racor and then connected that to the nut already on the pipe

Now, in place of my generic weepy filter I have an expensive weepy Racor - and a stripped thread!

Best to just cut the pipe and fit the compression fitting(with olive)? Should I cover the threads with some type of tape or should the compression fitting do it all?

Wot is 'best practice'?
 
nigelmercier said:
My new Racor Fuel Filter has 1/4"-18 NPTF threads. My pipework appears to have the same thread pitch, but tapered.

I'm sure this has been asked before, but is it OK to fit a tapered male into a parallel female?
Click to expand...

Its a common thing to do with plumbing but for diesel I think id want parallel to parallel tightening onto sealing washers.
 
obmij said:
Best to just cut the pipe and fit the compression fitting(with olive)? Should I cover the threads with some type of tape or should the compression fitting do it all?

Wot is 'best practice'?
Click to expand...

No tape should be needed on the threads of a compression fitting. The olive forms the seal.
 
nigelmercier said:
My new Racor Fuel Filter has 1/4"-18 NPTF threads. My pipework appears to have the same thread pitch, but tapered.

I'm sure this has been asked before, but is it OK to fit a tapered male into a parallel female?
Click to expand...

National Pipe Taper (Female) and BSPT are similar but do have variations to TPI. If the housing is aluminium then using even a brass BSPT male fitting could damage the thread, although it might simply deform to provide a nice tight seal.

I would use the tapered male with a good smear of loctite 577.

If you want specific fittings we use a firm in High Wycombe - Bearing Traders. There catalogue has virtually every combination of fitting adaptor you can think of, and sensible prices. http://www.bearingtraders.com
 
PCUK said:
No such thing as a female taper! In practice small bsp and npt work OK.
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Some times bsp and npt will fit. Some sizes have different tpi, but only by 1 thread per inch

The thread forms are different. One is a 55 degree thread, the other a 60 degree thread. If that is a problem it is possible to recut one to suit the other but it is a bit of a fudge.


Not so sure about there being no such thing as a female taper!
 
VicS said:
Some times bsp and npt will fit. Some sizes have different tpi, but only by 1 thread per inch

The thread forms are different. One is a 55 degree thread, the other a 60 degree thread. If that is a problem it is possible to recut one to suit the other but it is a bit of a fudge.


Not so sure about there being no such thing as a female taper!
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Taper female are v. rare in imperial threads, but the dryseal NPTF thread quoted in the OP are tapered male & female and have a modified 60 deg. thread form to ensure tight joints without packing. "F" stands for "fluid".
Mating NP and BSP can only be v. poor practice.
 
earlybird said:
... the dryseal NPTF thread quoted in the OP are tapered male & female and have a modified 60 deg. thread form to ensure tight joints without packing. "F" stands for "fluid". Mating NP and BSP can only be v. poor practice.
Click to expand...

I've got my calliper out and measured. It seems I was wrong (it was getting dark your honour), both the female ports and the male plugs are tapered. I was concerned because my pipework would only screw in two turns with hand pressure, but it seems the supplied plugs are the same.

Thanks for the replies and sorry to waste everyone's time. But I have learned a few things.

[Later] So the next questions are:

How tight do I do them?
Should I use any compound, or PTFE tape? I have Hylomar Universal Blue and Hylosil Instant Gasket (which seems to be silicone).
 
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nigelmercier said:
I've got my calliper out and measured. It seems I was wrong (it was getting dark your honour), both the female ports and the male plugs are tapered. I was concerned because my pipework would only screw in two turns with hand pressure, but it seems the supplied plugs are the same.

Thanks for the replies and sorry to waste everyone's time. But I have learned a few things.

[Later] So the next questions are:

How tight do I do them?
Should I use any compound, or PTFE tape? I have Hylomar Universal Blue and Hylosil Instant Gasket (which seems to be silicone).
Click to expand...

Nip and a bit. The hylomar will work fine, but if you can get some I cannot overstate just how effective Loctite 577 is for this application. I use it on brass taper anode plugs, as it seals without interfering with the electrical connection through the thread. It is also useful for refreshing old o rings.
 
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