Relief valve in piston

Relief valve in piston

Joined: September 25th, 2006, 2:19 pm

November 21st, 2011, 4:48 pm #1

This plan allows for adjustment from exterior of gun.

I kinda/sorta believe such relief valve might work when incorporated in a a pumper with a flat top piston. This is inspite of inducing a bit of headspace into the system.

I suspect that one would not have to count strokes once the relief valve is set to desired fps of the gun via chrony. Thinking that the valve would simply bleed off even at mid stroke.


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Joined: November 28th, 2002, 6:26 pm

November 21st, 2011, 4:55 pm #2

...where the valve is controlled by only by pressure acting on the wetted area of the valve itself, are difficult beasts to make regulate reliably. The least contamination - even water from condensation - seems to foul them up. I think that's because the wetted area of the valve seat is so small that the force available to open and close the valve is likewise small.

Too small for reliable accuracy.

http://www.network54.com/Forum/275684/m ... +new+idea-

Steve
Last edited by pneuguy on November 21st, 2011, 4:59 pm, edited 1 time in total.
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Joined: March 1st, 2002, 12:22 am

November 21st, 2011, 4:59 pm #3

This plan allows for adjustment from exterior of gun.

I kinda/sorta believe such relief valve might work when incorporated in a a pumper with a flat top piston. This is inspite of inducing a bit of headspace into the system.

I suspect that one would not have to count strokes once the relief valve is set to desired fps of the gun via chrony. Thinking that the valve would simply bleed off even at mid stroke.


The valve in the piston will open at some predetermined pressuire, and _not_ allow any more to be pushed in and stored?

 


dr_subsonic's pneumatic research lab

the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
Proud Sponsor of team_subsonic
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Joined: September 25th, 2006, 2:19 pm

November 21st, 2011, 5:44 pm #4

...where the valve is controlled by only by pressure acting on the wetted area of the valve itself, are difficult beasts to make regulate reliably. The least contamination - even water from condensation - seems to foul them up. I think that's because the wetted area of the valve seat is so small that the force available to open and close the valve is likewise small.

Too small for reliable accuracy.

http://www.network54.com/Forum/275684/m ... +new+idea-

Steve
..regulate the pressure captured in the valve or in the pump compression chamber? There is a huge difference, you know.

Ron



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Joined: April 28th, 2010, 12:23 am

November 21st, 2011, 5:48 pm #5

...where the valve is controlled by only by pressure acting on the wetted area of the valve itself, are difficult beasts to make regulate reliably. The least contamination - even water from condensation - seems to foul them up. I think that's because the wetted area of the valve seat is so small that the force available to open and close the valve is likewise small.

Too small for reliable accuracy.

http://www.network54.com/Forum/275684/m ... +new+idea-

Steve
pretty cool! nt
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Joined: April 28th, 2010, 12:23 am

November 21st, 2011, 6:19 pm #6

The valve in the piston will open at some predetermined pressuire, and _not_ allow any more to be pushed in and stored?

 


dr_subsonic's pneumatic research lab

the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
Proud Sponsor of team_subsonic
from what i read. so its a self regulating system that simply bleeds excessive pressure hence producing consistant velocities.
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Joined: November 28th, 2002, 6:26 pm

November 21st, 2011, 6:42 pm #7

..regulate the pressure captured in the valve or in the pump compression chamber? There is a huge difference, you know.

Ron


...between accumulated pressure in the valve and peak pumping pressure - as little as 10 or 20psi in fact. That's hardly "huge." I would have said something more like: Chump change.

But the answer to your question is "valve." It's very useful, by the way, to be able to have the valve's exhaust external, where you can hear the "hiss" and so have immediate (audible) feedback as to when to stop pumping.

Meanwhile, if regulation on the pump side is the specific goal, here's another way to defrock the feline. Here the sudden increase in piston bounceback when the spring starts generating headspace is the feedback to the shooter's pumping arm.



Steve
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Joined: April 28th, 2010, 12:23 am

November 21st, 2011, 7:43 pm #8

regulator that fits inside the pump tube??
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Joined: November 28th, 2002, 6:26 pm

November 21st, 2011, 9:56 pm #9

...that controls pressure by dumping excess air and pump strokes.


Steve
Last edited by pneuguy on November 22nd, 2011, 12:04 am, edited 1 time in total.
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Joined: September 25th, 2006, 2:19 pm

November 21st, 2011, 10:57 pm #10

...between accumulated pressure in the valve and peak pumping pressure - as little as 10 or 20psi in fact. That's hardly "huge." I would have said something more like: Chump change.

But the answer to your question is "valve." It's very useful, by the way, to be able to have the valve's exhaust external, where you can hear the "hiss" and so have immediate (audible) feedback as to when to stop pumping.

Meanwhile, if regulation on the pump side is the specific goal, here's another way to defrock the feline. Here the sudden increase in piston bounceback when the spring starts generating headspace is the feedback to the shooter's pumping arm.



Steve
because of the seal material shown in the link which might be delrin, teflon or nylon I would imagine.

These seal materials would be too rigid for the task. That is to say that any bit of debris cought between the seal surfaces tends to raise the complete poppet/valve from the seat thereby allowing greater leakage than a resilient valve would.

Now when the relief valve is applied to the valve, there must be zero leakage.We cannot accept anything less. Hence by utilizing a rigid seal, one has the propensity to apply more closing force than is needed. Otherwise less than perfect mating surfaces of the valve and seat will result in unnecessary target pressure fluctuations. That is why I show a resilient seal which should require only enough force differential to cause sealing which might even be forgiving of small specks of debris cought between the seal surfaces.

The "huge" difference I spoke of was not realative to psi but to what can be expected of the relief valve positioning.

Suppose there was a very small relief valve leak when placed on the valve. That would cause the valve to drain from target psi provided target psi could even be achieved.

But if you consider that very small leak in the relief valve when mounted in the piston, you could still reach target pressure. This would be possible because you only have the small leak leaking during the pulse of the stroke
where the pulse is not the entire timeline of the stroke but only a small fraction of the stroke which can only occur at end of the final stroke.

Do we need to hear a hissing sound?

Consider the last stroke where the piston is very near the valve compressing the air to be transferred into the valve. That is a very small volume of air so when the relief valve in the piston is overcome, I suspect the opperator is sure to feel the sudden letoff on the pump handle thereby the signal that valve charging pressure is obtained.
Last edited by oo7fuzz on November 21st, 2011, 11:06 pm, edited 1 time in total.
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