DCP system-possibly a new popet design for MROD

[shorty]

Decompression poppet system. Hey, it's the only thing I can come up with for a name.

Two poppets in one. One tiny one that fits into the main one. The purpose is to reduce cracking force to open the valve. Small one opens first releasing pressure on main poppet.

I don't have the know how experience turning down small parts like this but, thought the idea may be of service to the WAR valve without infringing  on the Cothran valve.

Similar idea of force reducing but different in simplicity and design.

What do you think?

[AmBraCol]

Funny, I was thinking about something similar, albeit different.  The idea of using a dual diameter single stroke pneumatic piston.  The larger diameter would sweep a lot of air into a smaller chamber then the smaller diameter would push it on into the firing chamber. Same principle only in reverse!   

[shorty]

Well,
I can't stop thinking how revolutionary this drop in poppet may be so, I ordered some micro steel tubing and drill rod. Can't wait to see where this goes. Just gonna have to figure out how to cut it without deformation. Got a 36" length so I guess there's plenty to mess up before it gets right.

Gonna have to think about a test jig as well. No way this will go in a gun with out a full bench test.

It's been a while since I measured a poppet stem for a Mrod. Anyone got a number on it?

[rsterne]

The stem on an MRod poppet is 1/8".... I am confused by where the pressure in the valve and reservoir is supposed to go to release the pressure on the main poppet?....

Bob

[Gertrude]

[Dairyboy]

Looking forward to how this turns out

[shorty]

As of right now, through the exit port or to the hammer. My first guess would be through the exit port then transfer port.

Don't know if it will really work but, glad your asking questions. Even though we don't see eye to eye (as I have said before), this might be better than statistics in a bikini.

Although, If I (we) pull it off, it will be pretty amazing. The concept really does sound interesting.

So, I just ordered 1/8"steel tubing with a .093" ID, .092" drill rod and .088" drill rod. The plans are to cut to length, make a PTFE or soft plastic 1st stage poppet and then use possibly a delrin or PVC secondary poppet.

Think of the poppet system like a decompression valve for a small engine.

[rsterne]

Believe me, I'm not playing Devil's Advocate here just to annoy you.... but here is what I see happening when the small valve opens.... I picked what I thought were reasonable numbers, you are quite at liberty to test the math with other numbers....

1. You have full pressure in the valve to start.... Let's say the valve plus reservoir volume is 215 cc (using the MRod for example) and the pressure is 3000 psi....

2. The diameter of the seal at the valve throat is 1/4", so the area of the seal is 0.049 sq.in.... and the force to open is 147 lbs....

3. The diameter of the seal on the mini-poppet is 3/32", so the area of the seal is 0.007 sq.in.... and the force to open is 21 lbs.... ie 1/7th of the total....

4. The hammer strikes the extended stem on the mini-poppet, which opens a small amount, and air begins to flow through the small area between the stem and inside of the main poppet tube into the (as drawn) exhaust port.... The pressure starts to drop, but you have 215 cc of air at 3000 psi to get rid of, and is it flowing out through the tiny vent hole in the side of the stem, so it doesn't drop very fast.... Cracking the mini-poppet used up "X" amount of hammer energy....

5. A microsecond later, or so, the hammer hits the end of the tubular main stem, which still has a force holding it closed of 147-21 = 126 lbs.... OK, so maybe the pressure might have dropped to 2900 psi (I'm being very generous here), so the force to open it is now 122 lbs.... To crack the remainder of the poppet off the seat takes (122/21) x "X" hammer energy.... The sum of the two is virtually identical to what it would have taken to do this in one step, but it occurs in two steps, a microsecond apart....

6. The only other thing I can see which could change this, is if the pressure in the exhaust port could rise, in that microsecond, to a high enough level to reduce the pressure differential across the main poppet seal.... If, for example, it could rise to 1000 psi, then the pressure across the seat would only be 2000 psi instead of 3000, so the opening force would be about 1/3 less.... However, if the pressure in the exhaust and transfer port rose to 1000 psi, the pellet would already be starting to move down the barrel, reducing the pressure in the exhaust port, and increasing the pressure differential across the main poppet, making it harder to open again....

If there is something in this sequence of events I have missed, please point it out.... That is entirely possible, I was just trying to think through the process, with some theoretical numbers to help me....

Bob

[shorty]

I did the math as well.

160lbs to 180lbs on the main poppet at 3000psi.  1st poppet at 46 to 82 lbs.

In hopes that the minor pressure release from the tube or increase in pressure (or both) in the atmosphere pressure area helps open the secondary poppet.

I am not sure what's gonna happen. Were gonna find out though. Your good at pointing holes in theories so, please keep them coming. It helps. It really does-seriously.

Your not annoying me.... This can be something big if it works out.

[rsterne]

I guess we'll find out.... The force and energy required can't be more.... however, "leaking" air into the exhaust port could be detrimental if the pellet starts to move before the main blast of air hits.... It will be like the valve opening slowly.... more slowly than normal.... The best valve profile would be a "square wave", closed - open - closed, with no gradual or partial opening like we have now.... which is roughly a parabola....

Bob

[MichaelM]

personally I am no engineer... but I cannot possibly see a airtube dropping enough pressure fast enough to make a difference unless it had a very small plenum so you would be pretty restricted on power output to begin with....


only other way it could work would be from it bleeding pressure to the exhaust side and causing less of a pressure differential...  but I would think that ANY difference in pellet fit would cause the pellet to move easier or harder making the pressure difference pretty random causing some pretty random velocities.... not to mention the random movement of the pellet putting it in different positions in the bore when the full blast would hit it to do the work......

also seems like you would need to vent the outer tube the center poppet rides in which would allow even less flow.... and make for some fragile tiny parts....


these was just a handful of random thoughts done early in the morning so I am not responsible for the cohesion or rambling that may or may not be happening lol

[shorty]

Things seem to be gong well until I got to the .088"drill rod. Really hard to grind that small by hand on the bench grinder. Need some better tools for that.

Concept is nearly finished and I think I will begin on a test jig. I am thinking PVC pipe with shop air to see if the concept works.

Although, while fitting parts together, this is a really easy way to make a poppet stem at 2 different dimensions instead of grinding it just behind the poppet.

[shorty]

Next

[shorty]

next

[shorty]

Made a test jig using some PVC pipe.

Well, it didn't work.

Test jig holds air and poppets hold air. Pressed on the small one first and it was super easy allowing a nice hissing sound. Got to the main and all air released.

Did this a couple times and then slipped a piece of tubing over the smaller poppet stem to by pass it. Felt like the same amount of pressure both ways.

60 to 80 psi shop air. I couldn't tell a difference so I call it a flop.

Atleast something came out of it though. Being able to reduce the stem diameter behind a poppet when you make your own poppet without grinding.

[Taso1000]

Shorty,

Great work!  I commend you for trying out your theory.  How many filament materials did Edison try before succeeding? He persisted and figured it out eventually.  We need to keep the ideas coming to advance our hobby!

Nothing ventured, nothing gained.  Kudos to you Sir!  :-)

Taso

[rsterne]

Yep, glad to see you carried through with it.... sorry it didn't work out, a simpler way to reduce opening force on a poppet would be great....

Bob