I have a union that I just can't get to seal. The fluid in the pipe is off-road diesel fuel. The pressure is less than 50 psi. The fitting is a 1-1/2 npt iron union with a brass face.

I'm getting desperate. I'm thinking about disassembling it (yet again... ), drying it off, and applying a bit of Rectorseal #7 to the brass face.

Anybody have experience, positive or negative, using a sealant on the face of a union?

Paul M.

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Originally Posted by clintonp

I have a union that I just can't get to seal. The fluid in the pipe is off-road diesel fuel. The pressure is less than 50 psi. The fitting is a 1-1/2 npt iron union with a brass face.

I'm getting desperate. I'm thinking about disassembling it (yet again...), drying it off, and applying a bit of Rectorseal #7 to the brass face.

Anybody have experience, positive or negative, using a sealant on the face of a union?

Paul M.

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I have no idea, but I know that Rectorseal is soluble in petroleum..

At least, it's soluble in Goo-Gone, which is petro-based.

How about an O-ring instead? Even if you had to use some axle grease to stick it in place while you tightened the union, it won't hurt the diesel when it washes away...

There wouldn't be a lot of rectorseal in the diesel, but it still doesn't sound like a good thing to me.

Another possibility would be to get some rubber sheet (old inner tube) and cut a gasket the right size..

Good luck!

When you say 'Rectorseal,' are you referring to the widely-used #5? I'm using #7 -- the only product I've found whose manufacturer says that it will hold up against off-road diesel fuel. Off-road diesel is just the same as regular diesel, except that it has a solvent-based red dye. The solvent attacks many sealants. Rectorseal says #7 is A-OK for off-road diesel. So far, they are right -- I've had no leaks using Rectorseal #7 --except for these @#$#@ unions!

I'm reluctant to try gasketting them; I don't want to open yet another can of worms... Still, I MUST come up with a solution.

One thing -- well, two things, really -- that I have not tried are lubing the threads of the union and lubing the parts of the union that drag as it's tightened. It might be that if I can get the collar to turn 'more freely,' I can torque it still further. I'm already using some pretty impressive pipe wrenches...

As for Rectorseal in the diesel fuel -- it's two 15,000 gallon tanks. I'm not concerned about a dab of Rectorseal getting loose!

Thanks for sharing your thoughts!

Paul M.

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Originally Posted by scirocco70

i have no idea, but i know that Rectorseal is soluble in petroleum..

At least, it's soluble in Goo-Gone, which is petro-based.

How about an O-ring instead? Even if you had to use some axle grease to stick it in place while you tightened the union, it won't hurt the diesel when it washes away...

There wouldn't be a lot of rectorseal in the diesel, but it still doesn't sound like a good thing to me.

Another possibility would be to get some rubber sheet (old inner tube) and cut a gasket the right size..

Good luck!

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Good points, and from the sound of it you've got a lot more experience than I do...

Cool!

A couple of other ideas (I like lubing the threads to get better clamping):

1) use a sanding block or other flat surface and some alum-oxide sandpaper to flatten the mating surfaces

2) maybe you can anneal/soften the sealing faces of the union?