Poppet Question for Bob

[JPSAXNC]

Hi Bob, I'm using a peek toilet plunger poppet, the diameter of the plunger is .250 with a 5 degree angle. The plunger begins to flatten out after a couple of shot strings. Do I need to increase the plunger angle or the plunger diameter, or both? Thanks

[JPSAXNC]

PS. The valve throat is .169 and the charge pressure is 3600psi.

[Motorhead]

Not bob .... But IMO run a 15* concave seat angle and 90* or flat face poppet

[JPSAXNC]

Hi Scott, Yes, that sounds like it would be more durable. So could I still use a .250 poppet diameter  over a .169 throat. I know the poppet would cover it, but do you think the poppet diameter should be bigger? Thanks

[Motorhead]

Due to the pressure your operating at, Poppet head POUNDING is going to be an issue.  Now generally I am running .025 to .040" sealing margins with PEEK poppets which taken to the larger margin would have your @ .170" throat sealing with a .250" poppet.  So where your at is a good place to start with the 15* seat profile suggestions.
So IMO you could drop size a bit, gain a tad easier opening valve at @ .220" if the degree of poppet recession appears to be better with the concave seat profile.

Bigger in poppet head is only going to INCREASE the force required to crack it open.  Also with greater area the force closing it will increase.

[JPSAXNC]

The problem I have is that  the air supply is tiny, so the slightest poppet bounce or chatter causes a major air loss. I need the same degree of stiction that the plunger type seal provides before it goes flat.

[Motorhead]

Are you using any sort of SSG or hammer de-bounce devise ?

[JPSAXNC]

There's no way to fit any type of de-bounce device. The gun uses a short stiff hammer spring that's shorter than the hammer stroke, so the hammer is free flight.

[JPSAXNC]

 I made a mistake. Originally the valve used a Delrin seat, since I was making a Peek poppet I thought I would make the seat out of Peek also. The Peek poppet hammered the Peek seat and eroded the surface of the seat. I made a new seat out of 304 stainless.

[rsterne]

If you make the seat a knife edge (concave on flat seat), it will flatten out until the closing force equals the compressive strength of the material.... and then stay at that width indefinitely....

Bob

[JPSAXNC]

Thanks Bob.

[luge007]

Can somone please elaborate on the poppet seat being "kinfe edge" with pictures/ diagrams please?


Also what is the advantage to running a 15 degree seat and a flat (?) faced poppet?  So then the outer edge of the poppet seats first on the conical seat, concentrating the pressure over a very small area (the outer corner/ edge of the poppet)?


I"m still learning the finer (ok basic) details of poppet/ valve design, please be constructive and understanding.
Cheers,
M

[nervoustrigger]

This:


Or you can apply the concave feature to the valve seat and use a flat poppet.  Either way, you get a concentration of force on a small sealing ring of the plastic poppet, encouraging it to deform on a microscopic scale to produce an airtight seal against the incompressible valve body.
 
My intuition tells me the concave poppet face is a little more forgiving of surface imperfections but in practice it seems like either one works nicely.

[Motorhead]

This:


Or you can apply the concave feature to the valve seat and use a flat poppet.  Either way, you get a concentration of force on a small sealing ring of the plastic poppet, encouraging it to deform on a microscopic scale to produce an airtight seal against the incompressible valve body.
 
My intuition tells me the concave poppet face is a little more forgiving of surface imperfections but in practice it seems like either one works nicely.

That would be a CONCAVE POPPET on a FLAT seat as shown.

A Concave SEAT has the angle and poppet is Flat at sealing surface.


I prefer Concave seats because the compressive force of poppet is slightly compressing the poppet INWARD at the seal being made at the outer most diameter or poppet head.

[nervoustrigger]

Oops, yeah I don’t know why I labeled the diagram that way.  Thanks for catching that, Scott.
 
Correctly labeled:

[luge007]

Thank You all, that makes more sense.