Author Topic: QB78 Leaks  (Read 5584 times)

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QB78 Leaks
« on: July 09, 2006, 06:05:34 AM »
I have a QB78 that leaks down fairly fast-- at least fast enough for the tube to get cold and sweat.  I do get a few shots, maybe a 3rd of normal, but they aren't as powerful as before.  I don't hear CO2 escaping, but perhaps my hearing is not that good.  Also, I don't feel any CO2 coming out of the barrel or the breech.  I'm wondering which seal this would be?

Bevo66

Offline Wallis

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Re: QB78 Leaks
« Reply #1 on: July 09, 2006, 07:21:35 AM »
are you buling or poweletts.

If you are buliking it's probably the washer inside the bulk fill adapter.

If you are powerletting it most likely the o-ring in the front cap.  The O-ring is a 19mm or 3/4 OD x 9/16 ID x3/32  you can get these at lowes or any hardware store.

HTH
Wallis
let\'s all have fun at what we do

  • Guest
Re: QB78 Leaks
« Reply #2 on: July 09, 2006, 09:36:42 AM »
Well, I have tried both the cartridges and the bulk, and the problem appears to be the same with both.  When I first charge the tube I don't hear anything.  But when I cock the bolt back I hear a rush of gas until I close the bolt.  After that I don't hear anything.

I just took it outside and charged it up on the bulk rig.  I shut off the valve to the bulk tank, and then I cocked it.  When I fired it, nothing happend--like it was out of gas, but it is charged up because the tube and the bulk fitting are cold as hell and sweating.  Outside, where I don't get any sound interference from fans or AC, I can hear the gas leaking out through the barrel.  You can distinctly hear the gas escaping but you can't feel it.  It appears now that the valve isn't working at all.  I am fairly certain it is not leaking at the endcap or bulk fitting.  I put some silicon grease on the o-rings on the endcap as well as the bulk fitting to make sure they were sealing good.

And now, I just went back to see if the pressure had bled down.  It had, so I was able to disconnect the bulk fitting and tank.  I don't hear the CO2 leaking as I put my ear up to the end of the barrel.  So, I guess it is the valve?

Bevo66

Offline Wallis

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Re: QB78 Leaks
« Reply #3 on: July 09, 2006, 09:39:57 AM »
Leaking thru the barrel sound like the steam seal is bad. You could also have some trash on the steam seal.  you can get a complete unit from archer airguns, or contact this gentleman and he can replaced the seal inthe stem, the web site is abarigun.com

Wallis
let\'s all have fun at what we do

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Re: QB78 Leaks
« Reply #4 on: July 09, 2006, 09:58:15 AM »
OK.

Tks, Bevo 66

  • Guest
Re: QB78 Leaks
« Reply #5 on: July 09, 2006, 12:02:47 PM »
Your leak could be a loose valve, the body of the valve will sometimes become loose and then the o-ring on the cap of the valve will not seal. A piece of 3/4 inch by 1/8 inch steel strap or a big screw driver will tighten it. If you need to remove the valve because it is leaking clean the seal on the valve stem and then check it with a magnifying glass, any dirt or shavings left in it can be gently scraped off and it will some times reseal, Alan at AB Airguns goes great work on resealing the stems.

  • Guest
QB78 Fixed
« Reply #6 on: July 12, 2006, 02:18:16 AM »
I broke down the gun and took the valve apart with Mike Melick's guidance .  I didn't see anything on the valve stem seal even with a magnifying glass, but I wiped the stem seal off with a towel and put everything back together.  The gun now holds gas again, shoots hard and straight, and I have learned how to maintain a QB78.

Much thanks is due Mike Melick for walking me through the disassembly over the phone.  They don't come any better than Mike.

Bevo66