Test of PEEK as a high pressure valve material

[Motorhead]

May also wish to look into Small HONDA gererators engine valves.  800-1500 watt stuff.
Think the O.S. model engine valves will end up a tad small for you guys ?
The O.S. Surpass 120's maybe

FS-120 Intake valve:

[rsterne]

Finally a few dimensions.... I'll add to this list as I get more.... How about a 0.559" face, Lloyd?....

OS FS-91 Intake valve is 26.2mm(1.031" ) tall, 3mm(.118" ) stem, and 11.2mm(.441" ) face.

OS FS120 exhaust valve is 32.6mm(1.283" ) tall, 3.5mm(.138" ) stem, and 12.2mm(.480" ) face. The intake valve has a 14.2mm(.559" ) face.

At the moment I have a few mid block Saito engines down, they all use the same valve, for both intake and exhaust.

 Head diameter is 0.470, stem diameter is 0.100, and the length overall is 1.025, all dimensions in inches. The FA-120 and larger Saito valves are larger.

 The OS and Enya valves are similar in size to the Saito line.

Bob

[csdilligaf]

  two questions.....Do you think glass filled Peek will be porous?  I do not get the same surface quality with glass filled anything.   Next, how hard to you need the valve to be?  55-58RC? I can machine some pretty hard stuff.

[lloyd-ss]

I don't know about the glass filled peek, but the glass filled delrin is not porous.
I think the stiffness of the valve material is very important as you don't want it flexing when the hammer hits.  I have punched the valve stem thru the valve head during a valve lock situation, so you the vavle heat tries to flex a lot.

I was reading on one of the physics forums and ran across a question that was so close to our situation that I had to smile.
The question asked how much "energy" does it take to lift a 2000 pound car off the ground.  I thought, "fairly simple, if you lift it a foot, then 2000 foot pounds." Wow, was I wrong.  One of the smart people answered it very well:
As you start lifting the car, at first you are just starting to unload the squish in the tires, so the first few inches are easy, then it starts to get harder.  Then as you continue, you start to unload the springs, and it gets heavier still.  Finally, when the springs are fully uncompressed and they start to leave the ground, only then do you feel the full 2000 pound load.  I think that is exactly what is happening in the PCP valve.  An increasing force gradient as the stem pushes on the valve and starts to change the valve head from concave to convex. I bet a lot of energy is used in flexing the valve head.
Lloyd

[SeanMP]

  Hahahaha
Scott
It's all good. Its still about PEEK but part of being geeky is a profound need to explore every possible tangent of a particular problem. We'll get there sooner or later...hopefully later and with a better understanding.

Bob
I am truly liking the idea of using a premanufactered valve. Those little widgits do take up an onerous amount of time to machine. My only concern is the length is a little short....BUT, I may be overestimating how much guide length I really need to stabilize the stem. Maybe it doesn't need to be captured all that well as the force would naturally settle it on the seat?? Yes no maybe?
Basic idea for me would be Throat depth + valve guide + .750 spring height (as Bob has razzed me in the past I'm intimately aware of what happens when you don't allow enough spring height )

Chip
Yes about 58C. I'm hardening O1 and tempering to 450F

Gents I'd be happy to make stems for anyones research proj. Sounds like Chip might be as well. He's machining stuff I machine stuff with....if ya know what I mean.

Lloyd
Yes I think all the time and movement just getting to the point of breaking the mass loose is absorbing a lot of your energy. I think if you can reduce that to minimums your going to be one giant step forward.

[SeanMP]

just as matter of interest here is a pic of some of the valves. Left is the current generation, middle is a .500" right is an early design the carried the seal on the stem.

[rsterne]

Lloyd, the seal material decompressing is the reason for the "1/2" in the FPE = 1/2 (force x distance) formula, as the initial force starts at zero, and only reaches full value (in your case 613 lbs.) just as the seal breaks free.... just like jacking up the car and unloading the tire sidewalls and the spring.... If there is energy being used to flex that seal material, it may be counterbalanced by the potential energy stored in the seal material during the compression of it on the previous cycle.... Yeah, there would be some heat generated and lost, but even if we get rid of the "1/2" in the equation, the FPE from decompressing the seat only goes from 1/4 FPE to 1/2 FPE.... I'm guessing that the 0.009" you measured as the deflection is only part of the story, because you weren't pushing on the stem to lift the valve clear, you were measuring it at "zero" stem load.... Just imagine the load on the end of the 3/16" stem pushing on the poppet head, not only compressing it there, but even stretching it between the end of the stem and the seat....

Sean, if you notice on that cross-section I emailed you, the valve seat and guide are intergral and incorporate a recessed spring seat so that the guide extends up inside the spring, allowing a shorter stem for a given stem and guide length.... Here is the pic I mean....



Bob

[rkr]

Hmm, why not use the valve seat from those engines as well? It's already well shaped for the purpose, just add an o-ring groove to the valve and embed that seat in the action.

[Big Bore Bart]

  These valve stems are easy to make.    I first soften the used auto valve with a torch and some firebrick.   Then chuck it up and start cutting.   I make the stem end first, that way the seat is perpendicular to the stem.  The spring seat is last.  A slight undercut as with plastic, allows a thinner margin and less lapping is required.   

Bob with your newer lathe, you should be able to crank these out by the dozen.    Mines a pre 1947 Atlas plain bearing 10"     You've even got Timken bearings.

The problem of wedging will still be there with any angle faced valve under the pressures we run in PCP's.

[Motorhead]

Hmm, why not use the valve seat from those engines as well? It's already well shaped for the purpose, just add an o-ring groove to the valve and embed that seat in the action.

Belief it or not ... but the guide and seat on these engines are bearing bronze.  Quite likely close to a 544 phosphor bronze.

In the engine application the spring rate is pretty low and valve is set down against seat softly via the cam profile as to NOT peen the seat.
Once valves closed the fuel burns and pressure spike is against an already closed valve.

an PCP air gun using the same valve COULD IN NO WAY use the same seat !!  The impact speed and pressure of the valve closing would mash & deform the seat in short order most likely.

Now having the STEM in bearing bronze or brass make far better sense than running in bare aluminum tho.

[lloyd-ss]

A lot of great ideas from everyone.  I am going to try something in the next few days and have a back to back comparison.
Lloyd

[Bill G]

Great point Scott.  Just wondering though, If the valve were tuned as Bob says, to close at 50% of barrel length, would it not be a much softer seating.  $64000 question is, how much is too much?  Obviously a cam driven valve has subtleties that are hard to match at any level.  Just a thought.  Then again, there is always going to be that guy who will operate one outside the specified parameter and ruin the valve. oops, no I've never done such a thing      .  I'm guessing that the operating duration are smaller with a PCP than a reciprocal combustion engine?? 

[rsterne]

Total duration of a PCP valve is about 1 msec, +-.... For an IC engine at 6000 RPM, that is 100 revs./sec, and an average valve is open for nearly 3/4 rev, so the duration is about 7.5 msec.... We're talking much shorter durations than an F1 engine, but then much smaller parts, too....

Bob

[PakProtector]

Total duration of a PCP valve is about 1 msec, +-.... For an IC engine at 6000 RPM, that is 100 revs./sec, and an average valve is open for nearly 3/4 rev, so the duration is about 7.5 msec.... We're talking much shorter durations than an F1 engine, but then much smaller parts, too....

Bob

LOL...maybe a sixties motorcycle GP 4-stroke from Honda maybe...23k red-lines...or maybe at most triple the duration of a PCP firing valve.

I also would suggest significant shortening of the valve stem, in an elastic fashion when the hammer strikes it. I have seen some rather silly stuff from rear-sprung valves. The tip where the hammer strikes it will be going full hammer velocity while the seat is still firmly stuck to its resting spot.
cheers,
Douglas

[Bill G]

that clears that up.  PCP is too fast for that seat

[lloyd-ss]

The comparison of PCP valves and engine valves is very interesting and something that I never really thought about.  But the PCP does usually have a smaller lift, correct?  I wonder if the acceleration and velocity of the two types of valves were mapped, how they would compare? I always assumed that the PCP valve had a lot less stress on it than an engine valve, even if the heat was ignored.
Lloyd

[rsterne]

Poppet valves typically have a lift of about 1/4 the diameter.... to get away from curtain effect and get maximum flow.... either in engines or PCPs.... The valves in engines can be much larger, of course, and therefore heavier.... The exhaust valve in a car opens against very high pressures, and high temperatures, so my gut feel is that the valve in a PCP has a much easier life.... I would be shocked if a valve (and seat) from a small engine wouldn't survive in a PCP....

Bob

[QVTom]

I'd have to agree that a PCPs life is easier.  In the case of the R/C 4 stroke, it was suggested  that the cam controls the closing rate preventing the rapid snapping shut of the valve like a PCP. Therefore, the bronze seat material would not be suitable for a PCP.  This is only partially correct in my view, these engines run 0.01" vale/rocker clearance, assuming a 1-1.5 rocker ratio the the last .015" of closure is uncontrolled.  Add the heat and millions of cycles I don't see why the R/C valve and seat would not work.

Tom

[PakProtector]

The PCP is opening the valve with no radial force. The engines can not claim that. The bronze guide no doubt helps the radial forces avoid chewing up the stem.
cheers,
Douglas

[QVTom]

^^ this too