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Tom West's Custom PC77 PumpMaster Classic Short Rifle

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December 15 2011 at 9:24 AM
Ron  (Login oo7fuzz)
Crosman Forum Member
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Response to The checkvalve never needs to open beyond a "bad leak." James Perotti...

The check valve never WILL open beyond a bad leak.It can't.

And the "bad leak" will manifest itself at the point of least seal resistance. There will always be points of a seal surface which are irregular because we earthlings cannot machine things perfect. So we resort to resilient seal material to help us out.

When the sealing is complete, there will be areas within the sealed surface which will not have the same normal force acting on the poppet due to irregular compression of the seal material. That's where the air will find a pathway into the valve.

So while air is being injected into the valve thru that leak, there is still much valve pressure on the face of the poppet. Any equilibrium will not be reached until the air can no longer pass thru the leak.

Truethfully, we would wish for the poppet to actually open up and provide a generous pathway to the reservoir. Our poppets would then last longer when we try to build high pressures in the valve.

That was a terrible problem with the pistol I built where I was loading the valve upwards of 4500psi. The compressed air got too hot and would burn a channel in the poppet. This would happen as the air was moved INTO the valve but I was unaware of the burned channel because the piston seal held up to the heat.

The following stroke got real exciting. When I pulled the lever off center, the pressure in the pump was now the full force of the valve and that wrenched the pistol from my hands and sent the gun flying across the garage floor.

Even though the burned channel was small it is surprising the amount of air it will exhaust when the valve pressure is 4500psi.

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