Help with 3/4in QEV

[jim_himself]

Hello, I've just started my first QEV air gun build and have run into an issue. The threads on my 3/4 to 1/2 (used for making my pilot) to fit into the QEV very well, I can only get about a turn. Both pieces are 3/4 and I don't know why they have different threads. I would appreciate any help with fixing the problem. If anyone has had this problem or knows of an adapter to fix it, that would be great.

Thanks in advance for any help

[Matt_NZ]

Hello, I've just started my first QEV air gun build and have run into an issue. The threads on my 3/4 to 1/2 (used for making my pilot) to fit into the QEV very well, I can only get about a turn. Both pieces are 3/4 and I don't know why they have different threads. I would appreciate any help with fixing the problem. If anyone has had this problem or knows of an adapter to fix it, that would be great.

Thanks in advance for any help

My guess is the two fittings have different types of thread.

The two common types of pipe thread are..

NPT American Standard Pipe Thread
BSPT British Standard Pipe Thread

So most likely the only fix is changing one of your 3/4" fittings, so they are both the same thread types.

[jim_himself]

Decided to go the "wrong" way. Covered the fitting in JB weld and twisted it in as far as i could, got it in pretty good without jb weld and it had a slow leak so I jb welded it and am waiting for it to dry then will try again.

[Ragnarok]

My guess is the two fittings have different types of thread.

Hmm. Usually, NPT and BSP are similar enough to be essentially interchangeable. The problem with mixing them is more likely to be slow leaks (usually fixed with generous PTFE tape) than them not fitting.

Also, one thing I should correct you on, the T in BSPT does not stand for "Thread", it stands for "Taper". This differentiates it from BSPP, where the second P stands for "Parallel".
I'm sure you can work it out from that, but for the benefit of any morons on the forum, BSPT has threads that get wider further up, BSPP remains the same diameter the whole way up.

[Matt_NZ]

My guess is the two fittings have different types of thread.

Also, one thing I should correct you on, the T in BSPT does not stand for "Thread", it stands for "Taper". This differentiates it from BSPP, where the second P stands for "Parallel".

I stand corrected. I knew it was British standard something.

[MrCrowley]

I do have a problem with the 3/4" 'American' QEVs not threading my brass BSP fittings very well. The NPT galv. iron fittings aren't much better really, perhaps they thread twice as far, which is not far at all considering the brass fittings only go about a turn and a half

[jim_himself]

Well jb weld and turning the crap out of it did the trick. No more leaks

[Crna Legija]

maybe its NPTF which if for fuel and high heat application so you cont need any sealant.

[Gun Freak]

@Jim, I think you went the wrong way with the JB Weld. It may have fixed the leak temporarily but it could spring another or maybe you will want to take out that fitting eventually if you make a change in the design. The better way to go would have been to find the correctly threaded fitting to use, but whatever floats your boat.

[bighead33]

well gun freak you beat me to.

[jim_himself]

GunFreak- im still gonna be able to get it out, i just wanted i quick solution for some initial testing, i intend to properly fix it as soon as i get time to run up to lowes, though i have no idea what fitting to get, but i will play with the fittings till i find something that works.

[Gun Freak]

Yeah well wood luck with that... you are going to have a REAL hard time getting it out. Properly mixed JB Weld can be pretty impossible to get out and if your fitting was a weak metal like brass then you will probably round out the fitting before you can get it out. I suggest going to the store with the actual valve and find a fitting that goes in further.

[jim_himself]

OK well i took out the fitting, it was hard, but it came out, i went to lowes and got the same reducer in black steel and it works fine now.

[Crna Legija]

At work we have a loctite for hydraulics and if you put it on 3/4inch pipe you cant get it off, you'd brake the fitting/pipe before it gives way.

[jim_himself]

U need to remember my fitting was only in a turn and a half. Also i put the pieces together and put the weld around the edges to make a shell of sorts[/list]