Canadian Airgun Forum

So I took the plunge.
It was only a matter of time.
This is only a prototype, as I'm not too sure if the poppet oring is gonna seal or not.
I decided to use a quad seal... Since they're designed to be used in a reciprocating application... And it just so happened that I had one the size I wanted to use.

Drilled the port thru the stem, at .046".
As it is now, I have .1" allowable lift, which will be taken into account when I design the hammer.

According to the math, it should take 68lbs force to crack the valve at 2500psi.

Well, think it'll work?

Very nice work

_________________
Sī vīs pācem, parā bellum

It's a work of art, and engineering! Did you make it out of stainless?

_________________

))))----//----------==
Iacio, ergo sum

Thanks guys.
No, it's aluminum. I don't imagine I'd get too far trying to make that out of stainless! Poor little lathe has a hard enough time as it is

I don't know if it will work or not but it is nice to look at.

_________________
Slavia 630/77 & 624, 1322, 1377, 2240, 2240/2260, WF600, Vantage .22, Falcon .22,
Talon .25, CR600W .22, PR900W .22, Stormrider .177 & sub 500fps .177,
Chaser .22, Chaser .22 HPA, Bandit/PP800 PCP .25, Artemis M11 .22, Webley Mk6 .177

It does look kinda like a rocket engine or something

There's a beefy exhaust port
(Actually it's getting a sleeve as a transfer port so the final porting won't be .34" as pictured.)

Just looking at it, I think you will find that the balancing piston is too large.... I have made them all the way from similar to that down to the balance piston about half the diameter of the poppet, and I have found that 65-75% works the best.... In fact, now I make mine 71%, so that the area is half the poppet seat area.... This reduces the cracking force by 50%, but still allows the valve to be tunable using hammer strike....

If the balance section is too large, the valve will "blow open", and can in fact stay open, dumping the reservoir.... If the areas are equal, you will likely create a dump valve that opens very easily (in fact may not seal up), but doesn't want to close.... I don't know what your dimensions are, this is just an observation.... As far as the workmanship goes, it looks first class, congratulations on that....

Bob

_________________
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!

Thanks Bob, that means a lot coming from you.

The way I have it now, the poppet area is .1" sq, and the piston is .075" sq.

That would make the piston 25% less than the poppet, or 75% of that total area.
Is that what you mean, by preferring a 71% ratio? or are you referring to the diameters alone?

I use 71% on the diameter, which is 50% on the area.... 75% on the area you will likely find the valve "blowing open", which means very difficult or impossible to tune with hammer strike.... The valve may work, but unless in a regulated PCP, will likely drop in velocity with each shot as the pressure drops, like a Cothran valve does.... Go too big and you may have trouble sealing it without a big valve spring....

You state 68 lbs. to crack it, but a 0.10 sq.in. poppet at 2500 psi would take 250 lbs. to crack it... The problem is that once it cracks, and before the vent has a chance to equalize the pressure inside the balance chamber, you will have about (250-68) = 182 lbs. of force blowing the valve open.... It will open that 0.1" of travel with quite a crash.... This can also cause failures of components, I know, I have had it happen....



I went too thin on the spider holding the balance chamber on that one, and the valve slamming open sheared the webs between the holes!.... .... I didn't allow for the impact of the mass of the poppet coming to a sudden stop against the balance chamber.... .... I have also had a poppet fail through the O-ring groove, there was insufficient land next to it (like yours), and the O-ring sheared through the end of the poppet.... .... There is about 180 lbs. force on the O-ring, trying to rip off the end of your poppet, when the valve is closed....

Bob

_________________
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!

Well, that puts a few more issues into perspective.
The forces blowing the valve open, and the force against the piston seal specifically.
I'll take your advice and re-design a few things.
I did read on the GTA, where someone mentioned sealing the balance piston with an internal oring in the chamber. That would eliminate the chance of losing the end of the piston.
I'll fix up my ratios as well.

Just for fun I did some playing.
Pressured it up and tapped the stem with a little hammer.
Albeit, the valve leaks pretty badly, and I don't have a spring in there at all. The valve seat needs work though.
But I managed to pump it up to 1000psi and tap away at it.
Yeah, big difference when compared to a conventional valve I built almost identical to this one. The hammer from a crosman 38t could open it with ease.


I remember seeing that picture of your valve on Google. I always thought it looked like it was broken. Now I get it

Fun stuff to play with for sure.

Initially made the valve stems from one piece of stainless...no separation at the oring, but more work to make.



Fellow on the gta (Motorhead) posted a pic of a stem with an aluminum head. Thought it was an excellent idea and it's worked out well on a few valves now. I do use a delrin seat insert in my valves though. Some QB valves...



Al

Those are sweet!
A set of qb valves in 3 different power levels?
What are the 2 on the left?

I have read through some of motorhead's posts, I did see his fancy poppet too... I thought I'd make something like it but wasn't sure about press fitting those parts together and still have them seal.

So I went with an internal oring in the balance chamber.
Had to make a workaround for the groove though.... By cross pinning the Little bushing end piece. Not sure what you'd call it. But it seems like it works.

Just need to cut a stem and drill it now.

So the balance piston is .19" and the poppet is .35"...
According to my math that should reduce the opening force from 196lbs to 138lbs at 2000psi. Not huge gains, but obviously I'd like to be able to tune it. It's going in a pistol so I don't necessarily need a ton of power. Just a lighter hammer, lighter trigger, etc...

I guess I could trim the poppet down a hair. I have .020" contact on the valve face as it is now. I've gotten away with using .010" before... Not sure what's really safe though before the poppet extrudes into the throat

Eureka!

It works. Meaning it sealed up nice and tight on the first fill attempt. I use a hand pump.
No valve spring.
That quad ring was a major pita to get in there though.

Well, using my very refined and scientific tapping hammer method... I can clearly tell that the valve is harder to open than it was with the first configuration I had going on.

It's holding strong at 1000psi anyway.
Pumping these things up for the first time always makes me nervous my wife would be some pissed if I blew myself up in the garage

Just some experiments The two on the left are the balanced valves, one for a 7/8" tube and one for a 1" tube (used on a .30 build). Later stems are grooved for an e clip that retains a light valve spring to aid with filling.