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Old 10-15-2006, 11:37 PM   #1 (permalink)
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Help with Sheridan valve

I'm having a problem with air leaking down the barrel of my bolt-action MacMurray Marauder. It's got a Constant-air conversion, with a 90 degree elbow sticking out the side, but I plugged that, and am using it with 12 grams. When I place a fresh 12 gram down the barrel, pull back on the bolt, and fire it, the 12 gram is punctured, but it just vents down the barrel. It vents in about 10-15 seconds.

It's a Sheridan valve, identical in parts and function. I tried replacing the pin-assembly with a different one I have, to no avail. So, I'm pretty sure it's not the cup seal...

I'm familiar with Sheridan valves, and have repaired the one in my KP, but this one is not responding to my 'trouble shooting.' Currently, I don't have it springed correctly, it won't do so much as burp a little... Any suggestions as to what else could be wrong? I checked out Mr. Big's thread on his leaking P-12, but nothing in there helped... Thanks in advance.
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Old 10-16-2006, 12:07 AM   #2 (permalink)
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check the valve body itself for any nicks. i'm tallking about the face of the brass piece that comes in contact with the cup seal onthe pierce pin.
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Old 10-16-2006, 01:25 AM   #3 (permalink)
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Try replacing the oring that the valve seats on. If all else fails just replace every valve seal you come in contact with. Also, make sure the valve nut is snugged down.

-Jake
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Old 10-16-2006, 11:31 AM   #4 (permalink)
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Chad, the valve body itself is clean, there is no damage. Jake, I think you may be onto something: when I tighten down the valve nut, it only snugs for about 1/4 turn. It seems like someone cross-threaded it, as this is the condition I received it in. I may need to send it to Palmers for a lower valve tube repair. I did this with my KP, and they fixed it so that the valve nut threads correctly.

If the valve nut is not totally secure though, why would this allow air to escape? The valve nut retains the valve body and guts, and does not push on the pierce pin assembly or have anything to do with the cup seal... It may need to be fixed anyway, but I wonder if that is truly causing the problem.

For consensus' sake, do you guys think that the valve nut not threading correctly is the source of the problem?
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Old 10-16-2006, 01:41 PM   #5 (permalink)
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Well there is an oring that seats the face of the valve to the steel pierce assembly. The jam nut puts pressure on the valve to hold it against the pierce assmebly. If the jam nut is'nt tightening down all the way it would allow a decent leak.

If your jam nut is cross threaded(which it sounds like it is) then your going to have issues sealing everything but the cup seal. If you take a peek in the "Sheridan Picture thread" and scroll to the bottom Latoolman posted a nice broken down pic of the innards of a KP. Look at the valve parts and you can see what I mean by the oring.

To determine if your jam nut is dicked up you can remove all the valve innards and attempt to thread just the jam nut on. It should thread in about a half inch with the guts removed.

-Jake
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Old 10-16-2006, 02:02 PM   #6 (permalink)
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I'm familiar with the parts of the valve, and I think you're right about the o-ring that seals against the steel pierce assembly. As far as the valve nut is concerned, it doesn't even seat more than 1/16" down. It bites the thread for about 1/4-turn, and stops. It appears to be angled slightly too. I'll send it to Palmers to have them clean out the threads.

Now that I think about it, the leak may not even be down the barrel. It's certainly not out of the front of the lower tube (the orange chamber face plug is in fine shape), but it kinda just leaks. So, I'll bet it's that o-ring on the face of the steel assembly that isn't sealing. Thanks for the advice, off to Palmers it goes!

Jason
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Old 10-16-2006, 03:20 PM   #7 (permalink)
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It may be cheaper to just buy a new valve nut than to send it to Palmers. I am making a purchase next week of a bunch of parts. I don't remember the price, but I think they were $2-$3 dollars for a new one.

If you interested let me know and I will add yours to my order and give you my paypal address.

**Edit (Remembered the site) They are $2.00 a piece. So that would be $2.39 and it is yours.

Last edited by MrBig; 10-16-2006 at 03:26 PM. Reason: Remembered the site.
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Old 10-16-2006, 03:52 PM   #8 (permalink)
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Hey Mr. Big,

Thanks for the offer, but it's actually the threading in the lower valve tube itself that is the problem. I had this same thing happen on my KP2, and ruined a new valve nut the first time I tried it! Once I sent it to Palmers, they re-tapped the tube for $15, and it works fine. I'm going to need to do the same thing with my Marauder, since I don't have a lathe (to keep the tap straight), and a 21/32-32 tap lying around!

Thanks for the offer though.
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