Has this ever been considered?

[mobilehomer]

Instead of a top hat shaped poppet, how about a ball? Seems like the sealing point would be better. Would the airflow be smoother? A spring guide could be added to the center of a SS style valve input in place of the orifice. The spring O.D. about 2/3 the O.D. of the ball. Just thinking outside the box.

[PikeP]

Instead of a top hat shaped poppet, how about a ball? Seems like the sealing point would be better. Would the airflow be smoother? A spring guide could be added to the center of a SS style valve input in place of the orifice. The spring O.D. about 2/3 the O.D. of the ball. Just thinking outside the box.

One of the biggest losses of 'flow efficiency' in our commonly used pcp valves is the 180 degree turn it makes as it enters the bore from your transfer plenum. That's why inline/air force valves outperform valves that are 180 out from bore by a nice margin that the valves 180 from bore out can never achieve..not only does the two 90 degree turns diminish some flow rate of air, so does the elevation of the transfer port itself.

Flow efficiency around the poppet may be good for something, nearly the same drag coefficient can be achieved with a conical shaped poppet as a spherical one, while a semi-sphere (half sphere) would be the best out of all 3 options, neither beats the other by any large margin so whichever of these 3 poppet designs you choose would likely work...

Now how much it aids in flow efficiency around the poppet is beyond me, I am sure it would help some...the only way to conclusively test this is to give it a go, make the two test conditions as close as possible minus the poppet design, record, rinse and repeat.  I don't think there is enough gains there to be worth my efforts, but if someone presented evidence that supported otherwise, I would be all about changing up my poppet! We can sit here and theorize all day, but until someone volunteers the time and effort we'll never know!

[rsterne]

I suggested a spherical poppet some time ago, but have never tried one....



The one shown above has the seat cut at 30 deg., and the sphere is incomplete from the seat contact to the stem, I thought a tangent from there to the stem made the most sense.... A hard material such as PEEK should resist deforming at the seat area the best, and a seat margin of 0.020" should be sufficient for most applications.... Don't forget that with any tapered seat, perfect concentricity is essential for sealing....

If you needed a valve spring, I would drill a pocket into the front of the sphere for it....

Bob

[a1rgunz]

FWIW - Here's a somewhat spherical poppet from a Sportsman 900:



And the valve seat:

[PikeP]

Looks like a crudely made custom poppet based on the machining marks and poppet material that sits below the seat..the area between the thinnest part of the stem all the way to where you can see the poppet head seats needs material removed unless the throat didn't need the slimming of the stem for flow to begin with, and its intent is purely to smooth the flow of air in a more streamlined way.

Hopefully one day someone takes 3 or 4 poppet designs, and run them across the chrony with no other changes made other than ensuring the valve is blown open all the way.

The larger the valve stem in the throat, and bolt probe tip in bore (if you run pin style opposed to blow thru/crescent moon shaped) the larger the separation of flow once air makes contact with it, doesn't matter if both setups run equal area for the air to pass through, the one with the smaller obstruction will absolutely outflow the one with a larger obstruction that creates a larger separation of air that is referred to as the boundary layer...

So finding all the ways to minimize the boundary layer in a pcp is great, will there be a poppet design that ultimately proves to create the smallest boundary layer leading to an increase in air flow and potential power output? I hope so, I am just too lazy to go build a bunch of poppets right now 

[JPSAXNC]

I'm currently using a spherical poppet, against a 90 degree seat.  They make the same power as a 5-7 degree toilet plunger type, run just as clean, (don't trap debris) are just as sticktionless, but far more durable than the toilet plunger design, with the same sealing area.

[JPSAXNC]

On the minus side, the spherical seal seems to be very bouncy. Even the SSG doesn't seem to be able to tame the bounce. I'm using a pretty heavy valve return spring, it takes 5 lbs. of force to crack the valve open against the spring. I'm ready to try a toilet plunger again.

[rkr]

Don't forget that with any tapered seat, perfect concentricity is essential for sealing....

Actually you don't need perfect alignment if you build a self centering valve like JB designed for BSA. The stem tunnel is larger than the valve stem and the stem is held in place by an o-ring that's in the valve tunnel. This allows slight tilting of shaft making it seal on conical seat even if it's not 100% concentric. Friction is also minimal if right size PTFE o-ring is used.

[Sbak]

On the minus side, the spherical seal seems to be very bouncy. Even the SSG doesn't seem to be able to tame the bounce. I'm using a pretty heavy valve return spring, it takes 5 lbs. of force to crack the valve open against the spring. I'm ready to try a toilet plunger again.

Thats actually quite interesting, how much overlap are you running on your plunger type poppets?

[rsterne]

The width of the seat margin required will depend on the material and pressure.... The harder the material and/or the lower the pressure, the narrower it can be.... I have used margins as small as 0.020" on PEEK poppets at under 3000 psi.... I don't go less than 0.030-0.035" on Delrin at that pressure, or it starts to extrude....

Bob

[JPSAXNC]

On the minus side, the spherical seal seems to be very bouncy. Even the SSG doesn't seem to be able to tame the bounce. I'm using a pretty heavy valve return spring, it takes 5 lbs. of force to crack the valve open against the spring. I'm ready to try a toilet plunger again.

Thats actually quite interesting, how much overlap are you running on your plunger type poppets? I had been using about .020 margins on the overlap, I made a new plunger with .050 over lap, hoping that the increased sealing area would help to control the valve bounce, and it did help at the cost of some velocity.

[PikeP]

I've run seat margins as low as .015" with peak, and .03" with delrin at my working pressures and seat OD. But I have a calculator that calculates practical margins for me that will keep the material from failing...so it depends on your working pressure range, and the size of the seat to determine optimal seat margin and material...

For example...

If I were to build a .177" caliber with a peek poppet on a .17"~ seat/throat and a max working pressure of 1500, I would go as low as a .0125" margin with peek.

If I were to build a .357" caliber with a peek poppet on a .362" seat/throat and max working pressure of 3000 I wouldn't really go lower then .025" for a seat margin personally...

Delrin would require at least twice the margin of the above.

[Sbak]

Thanks for the replies, my question had more to do with his observation of the spherical poppert being "bouncy" which i was interested in. That sounds to me like his poppet seat is cracking open more easily than he is accustomed to with a standard style poppet. I wanted to know his typical overlap to get a reference from one to the other. I too run 0.02-0.03 over throat diameter with peek for my poppets