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 Post subject: QB Valve O-ring Question
PostPosted: Sun May 19, 2013 10:55 pm 
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OK, you QB Gurus.... the standard setup is for the Valve O-ring to be tightened into the tube by snugging the two halves of the valve up once installed.... Any reason you couldn't use a standard 70D O-ring in the groove made between the two valve halves, adjusted for a bit of "squish", and then slid into place like the valve in a Disco?.... I'm talking HPA here, not CO2....

Bob

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PostPosted: Sun May 19, 2013 11:11 pm 
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Sound's doable wondering if it would leak from around the two halves of the valve though ?

Only one way to find out and that's to try it.

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PostPosted: Sun May 19, 2013 11:24 pm 
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I'm thinking you really only have to seal the rear half of the valve into the tube, the front half is just there to hold the O-ring in place.... Once under pressure, the O-ring should move "out and back" trying to wedge itself into the (few thou of) clearance in the 90* corner between the front face of the rear valve half and the outer tube.... right?....

It's been a while since I had a QB apart, and without the front half tightened in place the "groove" for the O-ring might be too deep and the O-ring might have trouble getting an initial seal against the tube.... Once pressurized, however, I would think the front half of the valve has nothing to do with the seal.... or am I crazy?....

Bob

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Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Mon May 20, 2013 10:01 am 
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rsterne wrote:
... the O-ring might have trouble getting an initial seal against the tube.... Once pressurized, however, I would think the front half of the valve has nothing to do with the seal.... or am I crazy?....

Bob


I doubt you're crazy...but I don't REALLY know you do I. :P

I haven't tried what you're referring to, but I see no reason why it shouldn't be fine if you can make that initial seal.

I have used floating o-rings in pumps (albeit at lower pressures) and they seal up just fine. The groove is ~.005-.010" wider than the o-ring cross section, and slightly deeper than normal as well. The o-ring does ride on the cylinder wall. With one "side" of the groove partially relieved, it makes an effective check valve.


Al


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PostPosted: Mon May 20, 2013 3:16 pm 
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Do you use any kind of O-ring lube? That might help too!

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PostPosted: Mon May 20, 2013 3:44 pm 
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I would use Dow 55 for a lube.... I'm thinking that the problem in obtaining an initial seal might be if the shoulder that the O-ring sits on, on the rear valve half, is too small in diameter.... and therefore the outside of the O-ring doesn't press hard enough against the tube to obtain an initial seal.... Tightening the two valve halves together squishes the O-ring, expanding the OD to avoid that problem of course....

I'll have to wait until my QB79 arrives to find out if what I'd like to do is possible.... I want to basically eliminate the front half of the valve, except for a thin threaded ring to just form an O-ring groove.... I'd assemble the ring onto the rear half with glue or loctite, let it dry, then stretch the O-ring into place afterwards, and slide the valve into the tube, leaving a large chamber between the rear valve half and the tank block as a plenum downstream of the regulator....

I would make a front spring seat from a rod threaded into the center of the tank block to hold and preload the valve spring.... As much as possible of the rear valve around the poppet would be removed to improve flow as well.... If I can't get it to seal, I may be able to make a shoulder or spacer to increase the diameter of the groove where the ID of the O-ring sits.... I figure that I should be able to get it to work somehow....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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