Modeling PCP Valve Lift and Dwell

[PakProtector]

With mention of this Ertalyte I went looking at its specs. Looks to be about 2/3 of the way to PEEK from Delrin, and at about Delrin cost. I am sticking wid PEEK; the cost/time spent making the part is WAAAAY bigger than the material cost, and I feel like pushing the stress up to where PEEK is required. For stuff like pellet shooters, where stress can be reduced significantly at the cost of only a little bit of performance this stuff looks *BRILLIANT*.
cheers,
Douglas

[rsterne]

rkr.... don't worry about it....

Bob

[QVTom]

Bob, the stoutest spring I was able to get into a RS was 2.75" OAL with 19lbs/in.  Preload was  2.413" and compressed was 1.238 with a 1.2"stroke.   rkr has increased his throw a bit and added an extra spring but you should be able to get close with these numbers.

Tom

[rsterne]

Thanks, Tom.... Your setup produces a hammer velocity of 30.48 fps, an energy of 1.843 FPE and a momentum of 0.121 ft.lb./sec.... Increasing the stroke to 1.413" (same spring) gives 34.88 fps, 2.414 FPE, and 0.138 ft.lb./sec....

For comparison, my .357 Hayabusa (240 FPE) hammer develops 1.561 FPE and 0.176 ft.lb./sec, so less energy but more momentum (hammer is 145 gr.).... A stock Disco hammer develops 0.247 FPE and 0.045 ft.lb./sec. even though the hammer weighs the same as rkr's.... The key in his installation is the stiff spring (which can be cocked with the side lever) and the long hammer travel.... which allows for the very light hammer.... Using your spring and rkr's travel results in a cocked force of 33.25 lbs....

Now that I see the math, it makes perfect sense....

Bob

[PakProtector]

Some further low hammer energy openings. Marauder, under perhaps 2600 psi. 2563 valve body and a PEEK head on an O1 stem. OE closing spring. While I had it apart last, I was measuring hammer throw, and possibilities for increasing same. I tried perhaps a tenth of an inch preload on the spring when the hammer was in cocked position and pulled the trigger. I got a rather loud POP from the exposed port. Doubt it was enough air to fire...repeated the experiment a few times and if the hammer could hit the stem, it cracked it open audibly.

Now...what in the heck does this mean? I couple this with stories of valve lock where the full hammer energy can't open the valve. The rate at which velocity declines as pressure increases seems like it should be linear...but I don't think it is.
cheers,
Douglas

[rsterne]

No doubt about it,, Douglas, it takes very little to "pop" a valve open enough to hear it, even against considerable pressure.... I have had it happen just dropping a hammer into the tube under it's own weight.... However, the valve opens so little that the closing force is equal to the entire force holding the valve shut, while the hammer energy is so small that it only opens a thou or two, not enough to fire....

You were using a PEEK head, so the compression in the head was tiny compared to say Delrin.... The amount of energy required to crack the valve is the force against the seat in lbs. times the compression distance in feet, over 2.... If the force is 120 lbs. and the compression is only 0.001", the FPE to crack the valve is.... 120 x 0.001 / 24 = 0.01 FPE hammer energy....

Bob

[srkhan]

seams like i'm seating in a math class room without being a math student!