External pipe fitting sealant

[Andrew]

Our diesel tank has developed a leak, going to be a pain to tighten all the fittings up though.

It’s only a drip, is there anything I can put on the outside to seal it?

It’s between the tank and the pump so very low pressure.

 

[Exfarmer]

Not sure where your leak is, but you do realise you have a running joint there?
Edited forget external sealants!

 

[pettsy]

I assume you can isolate the feed with the valve? I’ve used heldite jointing compound on oil pipes before so I assume would work on diesel too.

 

[Kidds]

Never tried it myself but a lot of folk say rub a bar of soap on it, as high a fat content soap as possible. (this one https://www.amazon.co.uk/Ivory-Simply-Bath-Bar-85g/dp/B0000536AR)

 

[Classichay]

Ptfe tape,

 

[Dry Rot]

I had an oil dip on my quad so did a search. HYLOMAR (liquid gasket) seemed to be highly recommended so I now use it on all joints. Seems to work, regardless of the liquid, but you need to put it on the joint before tightening up.

 

[Barleymow]

Soap works on plastic, might be worth a try

 

[dave mountain]

Turn the valve off, unscrew the union, unscrew all the fittings, clean them all off, healthy dose of loctite 55 on all the male threads, put it all back together. job done

 

[C.J]

I know what exfarmer meant by a running joint but I couldn't think what its "proper" name was.

"Threaded straight union " seems to be its technical name.

Basically you can split the pipework without having to start at the free end.

 

[dave mountain]

just known as a union. thats a stainless one in the picture above (316L), OP one is malleable iron. about an hours work tops to take that lot apart and reseal it properly. personally i would rip it out from the valve onwards and buy new, there are a lot of unnecessary joints there giving extra opportunity for leaks. should be a bush straight in the valve, barrel nipple, union, length of pipe, then the 45 and 90 mf elbows.

 

[thesilentone]

Not as bigger pain as you think, Pretty easy to take apart, thread tape on EVERY joint (as you more than likely will make another leak doing the repair.)

Why not just turn the tap off after each use, problem solved.

 

[dave mountain]

Not as bigger pain as you think, Pretty easy to take apart, thread tape on EVERY joint (as you more than likely will make another leak doing the repair.)

Why not just turn the tap off after each use, problem solved.

thread tape is very temperamental/unreliable on anything over 3/4 inch NB pipe, just use loctite 55 or any other decent thread cord

 

[thesilentone]

thread tape is very temperamental/unreliable on anything over 3/4 inch NB pipe, just use loctite 55 or any other decent thread cord

Well, I've used it for over 45 years with great success. in fact immediately after they used to pxss on a leaky joint to seal it..........

 

[pycoed]

The union (a "Dart Union") seals on the conical surfaces, so it's no good plastering loctite over the threads. You need the sealant on the cone & seat. The threads just hold the cone into the seat.
Same goes for PTFE on threads of compression fittings - it's the olive needs the PTFE (if old & leaky), not the threads, yet how many times do you see the tape sticking out around the backnut

 

[dave mountain]

Well, I've used it for over 45 years with great success. in fact immediately after they used to pxss on a leaky joint to seal it..........

i would guess you havent done all that much screwed pipework then. 45 years ago hemp and boss white would be the preffered joint, nowadays it is 55. never been ptfe apart from on small stuff, which is perhaps what you have been doing.

The union (a "Dart Union") seals on the conical surfaces, so it's no good plastering loctite over the threads. You need the sealant on the cone & seat. The threads just hold the cone into the seat.
Same goes for PTFE on threads of compression fittings - it's the olive needs the PTFE (if old & leaky), not the threads, yet how many times do you see the tape sticking out around the backnut

i assumed a basic level of knowledge, clearly i was wrong. obviously im talking about the actual screwed joints, and obviously you dont put thread cord on the nut of a union. also you should never put sealant on the cone and seat. if you are needing to put sealant inside an old union to get it to seal it is a bodge and the union should be replaced. agree that a lot a people (especially on farms) dont really understand what they are doing and put ptfe in all sorts of wierd and wonderful places, particularly on parallel threads.

 

[Av Gorritt]

Years back , when I worked in the business , we used to use Boss white and hemp on steam fittings , and a shellac type sealant on diesel fittings . Not sure you can buy it now but it was called "Osotite " Came in a small red can with a press-on lid , and was a bit messy if you didn't use care with it . But it certainly sealed diesel joints .