Delrin vs. PEEK Datasheet

[SeanMP]

Yessir I would skinny them up to .010 beyond the bevel. The PEEK seems to be lots strong enough

[PakProtector]

thanks for the drawing Sean. I will likely shrink the seat by reducing the head diameter; it is easier to take a bit off the head compared to removing some from a fragile valve body...
cheers,
Douglas

[rsterne]

Well I guess I'm overboard on my PEEK seat thicknesses.... It won't matter on the .25 Disco I just did, as the valve seat is on a 45* angle.... but on .308/.357 Hayabusa valve, I used the full 3/8" PEEK head on a 5/16" throat (with an ~0.010" bevelled corner).... IIRC I rounded the OD of the poppet slightly as well, but I think the seat is 0.020" - 0.025" wide.... Do you think it's better to leave the OD corner of the poppet absolutely square and the same size is the OD of the intended seat (ie throat ID plus .024").... or make the poppet fractionally bigger with a radius on the outside corner to ease the flow.... I'm not talking a lot, but maybe like I did on the Hayabusa, head 1/16" larger than throat, with both corners rounded off?....

Bob

[rjorge]

Another source for regular PEEK:

Amazon Prime - 2 Day free shipping 

[Motorhead]

Yessir I would skinny them up to .010 beyond the bevel. The PEEK seems to be lots strong enough

Where I feel uncomfortable with such a narrow sealing margin is the fact that while we try and keep a close Stem to body fit so minimal air loss's happens. We still have a tad bit of stem wiggle that is at it greatest further from the body hole stem is protruded.
* This so happens to be the MOST on the seat side, with any run out present effecting the TIR ( Total indicated run out ) of head diameter to throat leaves us not having much leeway to staying concentric and even around the whole seal margin.

Valid concern .. or not

[SeanMP]

Bob

I would trim the entire head in order to eliminate the shrouding rather than ease the transition around the shrouding. Just seems to make sense to keep the flow as straight as possible especially at this choke point where the risk of a sonic detonation is at it's highest.

Scott

I understand your concerns here. If your worried you could allow for a .012 seat margin.

If you think about how a drill works in a lathe it has to follow the axial center of the work. If it tried to drill off axis the lathe would make one revolution and the drill would snap off. Yes there is a tiny TIR but the worst I've ever seen is about .002.

In use the stem could tip over leaving a wedge shape gap but because the force is acting equally all around the poppet it will naturally straighten the poppet out against the seat. The only time I've had trouble with this is when the stem is really snug and there is not enough room to allow the poppet head (which when spun on the lathe showed it's seat was not true to the stem) to settle.