Balanced Valve - Big Bore MSP Project (Questions)
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Balanced Valve - Big Bore MSP Project (Questions)
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Topic: Balanced Valve - Big Bore MSP Project (Questions) (Read 817 times))
Duane38
Plinker
Posts: 291
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Real Name: Philip
Balanced Valve - Big Bore MSP Project (Questions)
«
on:
September 27, 2022, 02:54:04 PM »
Hey, gang. So, as the title would suggest...
First, is there any benefit of having a balanced valve in a pumper? What I am trying to achieve is a full dump. So far, that's not happening with the conventional striker and poppet design. I wanted to stay away from a blow open valve on this project to try something conventional.
One idea is to add design elements very similar to a balanced valve. Rather than drill a hole in the stem/poppet, design it to where the poppet head is in a tube separate from the valve at atmosphere, but without the hole.
Think I'll need that little hole.....
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Stafford, Va
Motorhead
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Re: Balanced Valve - Big Bore MSP Project (Questions)
«
Reply #1 on:
September 27, 2022, 03:49:12 PM »
Not necessarily balanced ... but an isolation of poppet area under pressure so when opened and sufficient hammer preload is present it will blow open and stay open.
In PCP's when we're taking sips of air WE DON'T WANT any hammer preload on poppet stem ... Pump gun would work best with preload IMO when you want Air Dump.
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Duane38
Plinker
Posts: 291
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Real Name: Philip
Re: Balanced Valve - Big Bore MSP Project (Questions)
«
Reply #2 on:
September 27, 2022, 04:39:08 PM »
So, by not drilling a hole in the stem under the poppet/air stream will work to keep it open?
What about a hole through the stem end to end that avoids the pressure wave? My sense is that would be the way to go as opposed to the other. I would think the other way with no way for air to escape, the poppet would act like a piston to rebound to it's rested state against the valve face.
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Stafford, Va
rsterne
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Re: Balanced Valve - Big Bore MSP Project (Questions)
«
Reply #3 on:
September 27, 2022, 04:51:07 PM »
If you vent a balanced valve through the center of the stem so that the balance chamber stays at atmospheric pressure, it should dump all the air.... only closing with the spring after the reservoir pressure has dropped to below the spring force.... Use a balance chamber of about 3/4 of the poppet seat diameter....
Bob
«
Last Edit: September 27, 2022, 04:54:05 PM by rsterne
»
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Duane38
Plinker
Posts: 291
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Real Name: Philip
Re: Balanced Valve - Big Bore MSP Project (Questions)
«
Reply #4 on:
September 27, 2022, 05:11:59 PM »
Thanks, Bob. That's kinda where my thought assumption was when studying the Balance design. Rather than using the high flow stream to meter the dwell, just have it remain at atmosphere.
Gonna give that a try and see what happens.
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Stafford, Va
Duane38
Plinker
Posts: 291
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Real Name: Philip
Re: Balanced Valve - Big Bore MSP Project (Questions)
«
Reply #5 on:
September 28, 2022, 09:36:24 PM »
Fiddling with the numbers...
The poppet head is .325 diameter. At 2kpsi, that's 150lbs! Yikes! No wonder it doesn't dump. Now, switching to the proposed design using .25 head diameter inside a chamber at atmosphere is removing 98lbs of load. Now left with 52lbs to crack open. Seems far more doable looking at it from that perspective.
Got the stem made up are near ready. Waiting on more material to arrive... Should be interesting. Will post pics when done this week.
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Stafford, Va
Rob M
GTA Senior Contributor
Posts: 6308
Re: Balanced Valve - Big Bore MSP Project (Questions)
«
Reply #6 on:
September 28, 2022, 09:44:46 PM »
Phil , in my experience with balanced valves , getting the poppet to seat initially is the challenge.( shy of filling from a tank rapidly ) Since theres now far less pressure acting on the poppet. I found a softer material like white nylon works for the seat , even if the head of the poppet is metal or delrin. The cothran valve actually uses a nylon poppet seat with a metal poppet head. which i found fascinating and kind of clarified my previous experiences.
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Louisiana
Duane38
Plinker
Posts: 291
yes
Real Name: Philip
Re: Balanced Valve - Big Bore MSP Project (Questions)
«
Reply #7 on:
September 29, 2022, 01:15:07 AM »
Yeah, I can see that application in a PCP indeed. This valve, cartridge style, is for a custom made big bore (9mm) project.
The gun needs to be able to fully dump the charge of air. The ratio of barrel volume to valve volume is such that the sweet spot is most beneficial when all the charged air is dumped.
This valve poppet is using an o'ring at the base which rests directly in the throat of the exhaust side. The poppet head shoulders on the exhaust.
I've drilled the stem fully through. This way, unlike a balanced valve, a great deal of the poppet head remains in atmosphere through the firing cycle. Somewhat an approach to a dump valve while using cocking and striking principles of a conventional valve.
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Stafford, Va
Brian W Cook
Shooter
Posts: 68
Re: Balanced Valve - Big Bore MSP Project (Questions)
«
Reply #8 on:
October 04, 2022, 07:15:01 PM »
How big is the inside of the reservoir that the valve is mounted in ? If you do a wagon wheel looking valve spring retainer with the ring of air holes around the outside it will let a conventional valve dump if you have a long e valve stem to push the poppet up into the low pressure area created by the ring of holes .
I had my .58 set up that way for a while .
It would dump the whole reservoir with a valve port of around .437 .
It wasn’t something i was doing on purpose it was a result of my quest for more air flow .
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Amazonia, Missouri
Duane38
Plinker
Posts: 291
yes
Real Name: Philip
Re: Balanced Valve - Big Bore MSP Project (Questions)
«
Reply #9 on:
October 05, 2022, 02:53:29 AM »
The throat of the valve is .312
Correct, the poppet head will be pushed into a chamber (tube) that is at atmosphere; valve stem hollow all the way through to poppet.
The valve is a cartridge valve with a final volume of .90cu.in./15cc in a multi-stroke pneumatic.
Each stroke produces 5.7cu.in/93cc. The goal here is to pump away to 2.5kpsi or higher. 20-25 strokes per shot.
I've already got all the parts machined and the gun ready to fire; find it rather easy to pump up. Ran into valve lock or not fully dumping. Almost ready to test the new valve poppet/atmosphere chamber idea. Had to wait for more brass stock to arrive.
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Stafford, Va
Duane38
Plinker
Posts: 291
yes
Real Name: Philip
Re: Balanced Valve - Big Bore MSP Project (Questions)
«
Reply #10 on:
October 11, 2022, 01:31:05 PM »
Finished!
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Stafford, Va
Duane38
Plinker
Posts: 291
yes
Real Name: Philip
Re: Balanced Valve - Big Bore MSP Project (Questions)
«
Reply #11 on:
October 11, 2022, 01:33:39 PM »
Inlet...and atmosphere chamber...
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Stafford, Va
Duane38
Plinker
Posts: 291
yes
Real Name: Philip
Re: Balanced Valve - Big Bore MSP Project (Questions)
«
Reply #12 on:
October 11, 2022, 01:42:49 PM »
Layout...
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Stafford, Va
Rob M
GTA Senior Contributor
Posts: 6308
Re: Balanced Valve - Big Bore MSP Project (Questions)
«
Reply #13 on:
October 11, 2022, 01:55:57 PM »
nice , this is a large valve , and i guess it needs to be for a 9mm pumper dumper
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Louisiana
Duane38
Plinker
Posts: 291
yes
Real Name: Philip
Re: Balanced Valve - Big Bore MSP Project (Questions)
«
Reply #14 on:
October 11, 2022, 02:08:26 PM »
Hey, Rob! Yes, sir. Big it is. Need some of that volume to give the pellet some umph.
It was 'finished'. Ran into it not dumping unless it had a silly heavy striker spring. In fact, it would fire 2-3 times. Not good for this application. LOL.
It's just shy 50 percent barrel volume (20 inch barrel) now and should do the trick. Soon I'll get it back together to test fire some pellets.
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Stafford, Va
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Balanced Valve - Big Bore MSP Project (Questions)