Thoughts on designing a better flowing valve

[sb327]

Not between the orings. Where the arrow is.

And my apologies, my wording messed things up.

I meant to say it needs a vent to atm where red arrow is. Let’s call that vent 2. That area always needs atm, and the barrel vent does not see atm while the valve is open and a pellet is still in barrel.

Your vent through the poppet, let’s call it vent 1, COULD be made large but adjustable by coming from the back (red line) with a screw adjuster.  That way you could tune how fast it closes.

I hope that clears that up. Sorry for the confusion.

Dave

[rsterne]

I think I understand Jack's first drawing in Reply #14, with the red valve able to stop the flow once the barrel pressure drops, to prevent dumping the entire plenum/reservoir.... Having it adjustable, so that you can control the amount of pressure drop makes total sense.... My concern is that if you allow too much flow past that valve, the pellet may reach the muzzle before it closes (terrible efficiency).... and conversely, if you have the clearance too small, it will slam shut very early in the shot cycle (low power).... Once it shuts, all the FPE from that moment on must come from the air trapped above it, and the pressure in that small volume will drop very quickly (think tiny plenum)....

It would appear to be a pretty fine balancing act, trying to create a dump valve where you can adjust the volume of air being dumped.... Might be simple in concept, but difficult to achieve in practice.... and ultimately restricted in FPE unless you will accept low efficiency.... either a one or the other choice if you are off just a bit in the adjustment and function.... JMO....

Bob

[jackssmirkingrevenge]

I hope that clears that up. Sorry for the confusion.

I think I understand, something like that?

It would appear to be a pretty fine balancing act, trying to create a dump valve where you can adjust the volume of air being dumped.... Might be simple in concept, but difficult to achieve in practice.... and ultimately restricted in FPE unless you will accept low efficiency.... either a one or the other choice if you are off just a bit in the adjustment and function.... JMO....

Thanks for chiming in Bob, agree that it sounds like it would be extremely fiddly.

One thing that struck me with the Huben however is that you're not really creating a separate firing chamber/plenum that is dumped for each shot while being shut off from the main reservoir.



The area shaded in red is the actual air volume between the outlet valve and the choking valve, it's extremely small - and there is no way dumping that tiny volume is going to give you 80 ft lbs in 0.22".  When you think about it, it makes sense that this volume should be as small as possible, because once the chocking valve actuates, anything past it is going to be dumped and you want to keep that to a bare minimum for the sake of efficiency.

[sb327]

That’s it!

That vent is need for proper operation but also as a safety. If forward oring leaked, it would have a bias to open the valve.

I may give that valve a go sometime. I think it has potential.

Dave

[jackssmirkingrevenge]

I may give that valve a go sometime. I think it has potential.

It certainly seems like it would be ideal for big bores.  The spool does not need to have a lot of bias so it can be opened with a relatively weak hammer, and since the flow goes direct in line with the barrel you do not have a lot of transfer volume. 

I wonder to what extent the adjustment screw would allow you to fine tune the closing speed though.

Here is the expected firing cycle animated for completeness sake:

[sb327]

My opinion would be that it (the vent) needs to be large. This would accommodate very fast closing.

Then, the taper on the adjustment screw be long and slender. Then you would have an adjustment that would not be super sensitive and could essentially be choked to where the valve would completely dump the reservoir.

I agree that this could be made to operate with a very light hammer and delrin or maybe ptfe for the seat.

Dave

[JuryRigger]

That is definitely an interesting setup... One other potential benefit of such a design (if it could be made efficient and tuneable, which has yet to be actually done), is the now extremely short action of the gun... If you look at the average tube, how many inches are lost to valve/hammer/spring/power adjuster that could be minimized with a setup like this? Could make for a big reservoir and long barrel in a short gun, and the action would only need to cock a very light spring and advance the mag...
Intriguing to say the least,
Jesse

[rsterne]

Jack I agree that in the Huben the vertical valve must be staying open long enough to allow enough air through to produce 80 FPE.... This means the efficiency is going to be related to having that valve close at exactly the right time so that the bullet has absorbed much of the energy in that air, but before it exits the muzzle.... I'm sure it can be done, but a lot of experimentation would have taken place to achieve exactly the right balance, I think.... and consistency of that dwell will be critical to producing a low ES....

Achieving the power should be relatively simple, if efficiency is not an issue, simply hold the valve open until the bullet exits.... That would be even easier to achieve because the barrel pressure would drop suddenly at that point, slamming the valve shut.... Basically a dump valve, being closed immediately after the bullet has exited.... This results in extremely low ES, but in my experience, also results in about 0.5 FPE/CI, however.... Closing the valve when the bullet is only halfway to the muzzle can give you about 0.9-1.0 FPE/CI.... even shorter dwells are required to get what these days is considered acceptable efficiency.... The shorter the dwell, the more consistent it must be or the ES suffers....

The theory is fine, but building it and achieving the power, efficiency, and low ES, all at the same time, will be the challenge....

Bob

[jackssmirkingrevenge]

I'm sure it can be done, but a lot of experimentation would have taken place to achieve exactly the right balance, I think.... and consistency of that dwell will be critical to producing a low ES...

No doubt that the choking valve would need to be extremely and finely adjustable.

I am still not clear on how the Huben does it exactly.

The chocking valve has its own return spring that is not adjustable:



There is however a second adjustable element that is used for tuning, I haven't figured this out yet.



There is a pneumatic element to it, the bottom of the pin seems to have a seal in the housing and possibly a bleed hole at the base:

[sb327]

From how I understand it

The spring at the closing valve only effects it once the chambers are equalized after a shot. It just brings the closing valve back open.

The red spring is a lot stronger. It is biased to close the valve. When the valve is at full pressure, the effect that pressure has on the stem for red spring (seal at bottom) compresses red spring allowing closing valve to open. Ready to fire.

Depending on how tight red spring is adjusted vs pressure in valve, it will close closing valve when pressure drops low enough.

That’s just my take on it.

Dave

[jackssmirkingrevenge]

That’s just my take on it.

Makes sense, something like that:

[sb327]

That’s about it!

Need atm to outside for stem.

Spring tension adjustable. Will need oring added for that piece that I show threaded.

You could technically show a larger path from plenum air to spring. That would indicate a fast response to pressure change.

Man, your salty with this stuff.

Dave

[jackssmirkingrevenge]

There we go:

[CableStop]

Wouldn't this whole cut off valve issue be solved with a regulator?  That should cause enough of a pressure drop to actuate the valve.

[rsterne]

That would depend on the plenum volume, which dictates how quickly the pressure drops at the valve seat....

Bob

[sb327]

And how low the pressure would be.

I was thinking about this valve the other day. Looking at the rear portion of the poppet, it appears the sear must hold a substantial force. Force enough that can open poppet, overcome oring breakout friction and compress spring.

To make this where you used reg and plenum size to control closing, the pressure upon closing would either be very low or the return spring would be very large. So large that it would not open reliably.

The way designed, it can close at a higher pressure since it is dependent upon a small rod/heavy spring. This allows independent control and does not effecting poppet opening. A two poppet system, so to speak.

 It does still require a pressure drop, so plenum size still contributes to overall performance in a large way.

Dave

[CableStop]

Since either solution requires a plenum area where the pressure drops, either solution should have roughly the same efficiency right? I had briefly thought one advantage of the valve as designed is that the exhaust always sees tank pressure. Then I remembered that the valve body is essentially a plenum and that the exhaust pressure will drop as the plenum empties.

I realize now why this design is more tunable, especially with external adjuments. The only way I can see a regulator working is if it had a telescoping plenum.

[rsterne]

IMO the valve body is only a plenum if the inlet is significantly smaller than the outlet.... If the inlet area is large, the pressure inside the valve will approximate reservoir pressure during the shot cycle.... This all changes once the "choking valve" starts to close.... or even if the area for the HPA to pass through it is significantly less than the smallest port downstream of it....

Bob