5 replies to this topic

[Broderick]

EDIT: Okay, if you're going to read the below text, the one tank that still leaks is leaking out of the barrel; the back is fine. What can I do to fix this? Just goop around it?
Alright, so a couple weeks ago I got a Big Salvo from a garage sale, and it worked just fine; good pump, tanks held pressure just fine, and didn't leak. Then I dremeled off the AR plates on the front, and checked to make sure the air tanks were'nt leaking, because I've heard the gun is really finicky. Still nothing, so I took a small sanding drum and sanded it out a little bit. Then all 4 were leaking. Now, I really don't understand how these tanks work, I've heard them being called "backpressure tanks", and having the 4 stage trigger. I thought that maybe some debris got into the tank, because I've heard that can also cause them to leak. Nothing came out, so I went and took a bit of compressed air and blew that in there to make sure nothing was in there. They were all clear, but still leaked. So today I went and sealed up the backs with Plumbers Goop, since that's where I thought they were leaking from. It worked for 3 of them, so that's awesome, but one is still leaking, and I've COATED the entire back with goop, and still leaking. It's not the tubing, I know it's coming from the tank itself. Could it be leaking out the barrel somehow...? I'm not really sure what to do here.
Here's a couple pics if it helps, but it's rather hard to see up close, considering my only camera is off of my cell phone.


Here's the barrel, there's no visible debris in there, apart from one glob of plastic that you can see that was already there, when it worked. I've tried moving it with my finger, but it must be melted.


Any input would be appreciated.

Edited by Broderick, 30 May 2010 - 10:47 PM.

[jaybo1996]

Are you sure the tank is leaking air? It may be the trigger system. I don't know much about back pressure, but the Cobra I own ometimes doesn't seal while pumping it, it's a 50-50 chance, and if you point the barrel down while pumping, it jumps to 70-30.

Edited by jaybo1996, 30 May 2010 - 07:19 PM.

[Broderick]

Are you sure the tank is leaking air? It may be the trigger system. I don't know much about back pressure, but the Cobra I own ometimes doesn't seal while pumping it, it's a 50-50 chance, and if you point the barrel down while pumping, it jumps to 70-30.

I have a Cobra too, and it occasionally leaks. I know it has to be the tanks though, since I can put my ear against the barrel and hear it leak. I've listened closer to the trigger mechanism and I can tell it's coming from the tank. The trigger system has a very good seal, since it uses and o-ring to seal with the inside and release air... somehow. It's got lots of the original lube left on it. I've read Carbon's thread on this thinking it may have an answer to this, but his problems were'nt the same ones I'm having. Thanks for the reply though.

Edited by Broderick, 30 May 2010 - 07:26 PM.

[Kabigon]

To check where the tank leaks at, pump it up and put it underwater. Where the air bubbles are coming from is where its leaking.

[Broderick]

To check where the tank leaks at, pump it up and put it underwater. Where the air bubbles are coming from is where its leaking.

It's not where the leak is coming from that's really the problem. The tubing isn't long enough to put under the water, and I don't really feel like detaching it and re-applying it.
I guess my real question is, how do I seal up such a leak?

[Broderick]

If you have a Cobra, you can simply unscrew it, and learn how backpressure tanks work. They almost never leak in any way you can use a sealant on, because it's the critical sealing surface of the outlet valve itself. Also, post #2 in the autopsy pictures thread shows a Big Salvo tank opened up.

From your initial description, it is almost a certainty that you've put crud in the seal area. Probably plastic dust from the sanding. If you blew it back inward using compressed air from the barrel end, then you may never get it all out. Since you mention having a compressor, I recommend holding the tank pointing downward, then repeatedly applying and releasing pressure to get the piston moving. Other than opening it up, there's pretty much no choice but to keep working at blowing out the debris. There's just too many angles and projections inside for one blast of air to clear out.

Another possibility is that the debris being in there has damaged the surface of the seal. If that's the case, you're going to have to cut the tank(s) open to restore those surfaces. Or just buy another Big Salvo.

Thanks, I just went with the Cobra and fired some air in there with the gun pointed down a few times, and I got the tank to hold pressure fine. Not sure how long it will work, but now I know what the probable cause of failure like this is.
Problem solved, thanks a bunch guys.