If something's air tight, is it fuel tight?

[Jesus-Ninja]

I'm fitting a sard AFPR which has threaded holes into which go 3 threaded hard stubs. One goes to the return to tank (low pressure), one goes to the fuel rail (high pressure) and the other I am teeing into an oil filled pressure gauge for under the bonnet to set the pressure and a pressure sensor to go to an electrical gauge in the cabin. So all in all I have a few joints, none of which I'd want to let go.

So I figured I'd pressure test the high pressure connections by connecting one to a source of air (a foot pump as it happens) and blocking the other off with a bit of pipe with a bolt in the end.

If it holds air pressure, is it same to assume it will hold fuel pressure. I believe so, but would like the warm fuzzy feeling of agreement from peopl with more brain cells than me. :D

[richy rich]

yes if it will hold air it will hold liquid.

As a plumber I use air to check pipe work and I've never had a water leak if it has held air.

Q1 what pressure are you checking it at.
Q2 how long are you holding the pressure.

[Jesus-Ninja]

Cheers Rich - well, the regulator currently opens up at 60 psi so blocking that off, I can go above, although I'm not sure if this will damage the regulator, but I suspect not. Probably about 80 psi?

I have discovered that my pump leaks though, so I have to clamp the hose on the pump once it's up to pressure.

I've been using a paint brush to slap some soapy water over the joints to look for leaks.

It's more to test that it's not going to instantly p!ss fuel everywhere. Folk fit these with out testing so this is more belt and braces.

[Jesus-Ninja]

Well that was worth while. At first I got it up to pressure and it was clamped up and holding pressure, so I went to make a sandwich, only to find that upon my return the pressure had dropped. Pumped it up again, but it wouldn't hold. I then found a split brass fitting. This has obviously let go after a few minutes of pressure. I was probably a bit enthusiastic. Glad I tested it!

So, second attempt (put the gauge directly into a steel fitting. My leaky foot pump didn't help, but I managed to clamp off the system at 73psi, and it's been holding that for 10 minutes now. I wonder how long I should leave it for?

[richy rich]

Id leave it for 30 to 60 mins myself.

[Jesus-Ninja]

Id leave it for 30 to 60 mins myself.

Well, over an hour on and it's dropped from 73 psi to a smidge over 72.

I reckon that's OK, as it's air, not fuel, and it's probably coming from one of two hoses clamped with mole grips, and the air would have been warmed when being pumped in under pressure and will undoubtedly have cooled a little.

[richy rich]

Id say a ok.

[Jesus-Ninja]

Id say a ok.

Yeah - all in and fitted and working a treat. Thanks for your help, Rich. :)

[richy rich]

Yeah - all in and fitted and working a treat. Thanks for your help, Rich. :)
No prob

ps have you finished your track car Ive only managed to get a few pages in to your thread looks like some project.

[Jesus-Ninja]

No prob

ps have you finished your track car Ive only managed to get a few pages in to your thread looks like some project.

Ha! NO! :D

The legnum has kind of taken over my spare time, short term. I'm trying to get that as ship shape as possible in as short-a-time as possible, so that I have a toy to play with (trackdays, sunday drives, and the odd mechanical tinkering), and then in's all hands on deck again with the project.

It's bogged down in body work at the moment, but once I get the nose done (buck, moulds and finished piece) I think it'll be down hill for the rest of the shell, both literally and psychologically. With the shell done it will be a real pleasure to work on again - every job a new challenge and different, instead of what currently seems to be a wilderness of isopon and primer!

I already have ideas for the next space frame though, LOL.

[Turbo_Steve]

er...ship shape is an MOT and a service, not modifying it, mate :D

[Jesus-Ninja]

er...ship shape is an MOT and a service, not modifying it, mate :D

LOL :) I plan to sail on rougher seas :D

Actually, that's a point, when IS my MOT due........?