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All Springer/NP/PCP Air Gun Discussion General > "Bob and Lloyds Workshop"

Lloyd Has Been Busy Again! - Valve Pressure Testing!

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rsterne:
We have been in contact with Dr. Geoffrey Kolbe (yes, the Drag & Twist calculator guru) recently, as he is writing a book on the Internal Ballistics of Firearms, and is going to be including a chapter on PCP airguns....  During our discussions, he asked if anyone had investigated the pressure rise time and losses across a PCP valve, and of course Lloyd immediately took up the challenge.... All the photos here were taken by Lloyd, and are the property of Long Range LLC, Lloyd Sikes, who holds the Copyright, and must give his permission for their use (which I have)....

First of all, a sketch of the layout of the instrumentation, followed by a photo of the pressure sensor and location....







Since initial testing, Lloyd has changed the hammer sensing from a sliding contact to one that electrically senses hammer contact with the valve stem, to get rid of noise.... Here are the oscilloscope traces, taken at an air pressure of 1270 psi.... The upper (blue) trace is the pressure, and the lower (red) one is the hammer.... The first is at 5 mSec. per horizontal division, and clearly shows air-wasting hammer bounce.... It is about 15 mSec. after initial hammer contact, by which time any pellet would have left the muzzle....



The second is a 0.5 mSec, per division, and shows the valve pressure rise time in detail.... Vertical divisions on the O-scope trace are 500 psi high in both cases....



There is a huge amount of information contained in just these two traces.... Lloyd has duplicated them at 500 psi and 2030 psi as well.... So far, there is no barrel attached, the decrease in pressure at the sensor after the peak is due to slight leakage, likely where it is clamped to the transfer port.... The reservoir is 45 cc, and the wasted volume in the sensor is 0.22 cc.... As this testing progresses, I will post more information in this thread.... My thanks to my friend Lloyd for sharing this with us....

Bob

Spacebus:
Do airgun mfgs measure this kind of thing? I feel like hammer bounce prevention should be built into PCPs.

rsterne:
It's not that hard to do.... Either an SSG (Stopping Spring Guide) or even an SSS (Short Stiff Spring) does wonders.... The SSS is harder to cock, while the SSG can be easier than a conventional preloaded hammer, if it's designed correctly.... These tests don't mean much as yet, but once the barrel is attached, the area under the curve should represent the air lost to hammer bounce....

Bob

HunterWhite:
Amazing 😄.
This is the kind of stuff that keeps the airgun endeavor interesting 🤔.

Hunter

mobilemail:
Boy, it's about time Lloyd does something beside spoil those darn grandkids!!!   ;D ;D ;D ;D

Thanks Lloyd, and I hope you're having fun!!!!  I miss seeing you at the fun shoots.

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