Pet cock leaks when opening it

[three4rd]

I bought a new shut-off valve and put it in. Are these things tapered? It screwed in fine, and then I checked to see if the amount of exposed threads is about the same as the old one, which it is. So added some gas, checked for leaks, etc. All good. Gradually added more gas, checked for leaks. Hooked up the gas line, checked for flow, filled the tank, THEN noticed that some gas is showing up at the top of the threads. Darn!!! I tightened the valve just a bit more but doing so not only didn't stop the leak but also turns the gas line over too far and so starts to interfere with the throttle. Would it have been better to go around another turn yet (which takes me back to whether it is tapered inside the tank)? It seemed tight enough and as though another full turn might have been a bit too much. The old one certainly backed off without seeming real tight. Possibly some dirt got caught in the threads after removing the old one? No longer a leak down through the stem but now I have the leak between the tank and valve. So.....what? Re-drain the tank and take out the valve again? Plumber's tape? I hate leaks of any kind. Weird how the leak didn't show up till nearly 20 minutes later. (Figures that it would wait to start till I had all the gas back in the tank!) Did it take the additional pressure of the full tank of gas to start forcing some through wherever it's getting past the threads?

[Vrobert]

did you use thread sealer? tape or paste is fine. if it needs to point a certain direction use tape so you'll get more turns without over tightening

[three4rd]

Didn't use anything on it. Right now I've been turning it a bit tighter very gradually and then rechecking it. I can see where - even though it was lined up at about the same position as the old - I could actually turn it just by moving the gas line around - so obviously it really wasn't tight enough (probably could have been, as you say, with some tape on it - didn't think to do that cause there was nothing on the old (probably original?) one. The angle at this point is a bit off but - if the leak stops - I can always loosen and move the gas tank over just a bit and/or get a longer piece of gas line. It's really too short now as it is. When I first installed an in-line filter, I wound up cutting the one piece a bit too short. Right now I have the gas line passing on the inside of the throttle mechanism - might be able to move it to the outside. Trying to avoid re-draining the tank and taking the new valve back out if possible, but if that's what has to be done, no real problem.

[Vrobert]

For future reference, tapered threads always need a thread sealer of some sort. You may get it to stop leaking by more tightening but you will probably ruin the threads.

[three4rd]

...meaning ruin them inside the tank...? I don't think I'll tighten any further. I'm about 45 degrees from the original position. It's barely leaking anymore - but still some gas evident on the one side of the valve. If it doesn't completely stop I'll have to take it back out. I have plumber's tape. Either way, I imagine retightening it (even if removing it again) will never go back to the original position so I have to get more fuel line.

[Vrobert]

The threads can be damaged on the tank and the petcock. If you wrap about 4 layers of teflon tape on the petcock you'll be able to rotate it to any position you like.

[three4rd]

Still leaking. Going to have to take it back out. Wish I wouldn't have filled the tank. Next time I won't till I'm absolutely sure I can get this to work. Took apart the old one - all that's in there is a rubber o-ring. What is the 'worn packing' that I was told about as being the cause of the problem?

Been researching this and it seems that teflon tape is not suggested. Gas will eat through it eventually. Also, many people say they have never used anything when installing these and never had any problems. Loctite perhaps?

[cooperino]

Originally Posted by three4rd

Still leaking. Going to have to take it back out. Wish I wouldn't have filled the tank. Next time I won't till I'm absolutely sure I can get this to work. Took apart the old one - all that's in there is a rubber o-ring. What is the 'worn packing' that I was told about as being the cause of the problem?

Been researching this and it seems that teflon tape is not suggested. Gas will eat through it eventually. Also, many people say they have never used anything when installing these and never had any problems. Loctite perhaps?

Correct. you need to use thread tape or dope that is meant for gasoline. When applying tape you want to apply enough that it starts to tighten pretty quickly in the threads. starting to thread in at different positions can help in ending up in correct position. It may take a time or 2 to get it tight and in correct rotation.

I use the yellow gas line thread tape for gasoline. It is double the density of the white PTFE. It holds up better to gasoline and other types of liquid and vapor gases.

[three4rd]

Originally Posted by cooperino

Correct. you need to use thread tape or dope that is meant for gasoline. When applying tape you want to apply enough that it starts to tighten pretty quickly in the threads. starting to thread in at different positions can help in ending up in correct position. It may take a time or 2 to get it tight and in correct rotation.

I use the yellow gas line thread tape for gasoline. It is double the density of the white PTFE. It holds up better to gasoline and other types of liquid and vapor gases.

Coop...I assume you're referring to this stuff..https://www.homedepot.com/p/Oatey-1-...kizec1dU17BzQ0

So you'd suggest that over some sort of loctite / permatex?

[twoton]

Don't take it personally, lots of crappy threaded parts come out of China. Poor attention to tolerances.

All the plumbers I've known always use both dope on the female threads AND tape on the male threads.