Lloyd Has Been Busy Again! - Valve Pressure Testing!

[lloyd-ss]

Stan, Please, no concern whatsoever!
I remember that thread by George and the great lengths he went to. Hi arsenal of electronic equipment and knowledge of how to use it far exceeds mine.
Right now I am trying to establish what I consider to be a solid, repeatable baseline. There is a plan to eventually install a second sensor to measure pressure drops across the valve but it will take several iterations to get it right. It will take some time but it should be honest data.
Lloyd

[WhatUPSbox?]

Lloyd, in that long thread, there were a couple of things that may be relevant.
In this post https://www.gatewaytoairguns.org/GTA/index.php?topic=137566.msg1523638#msg1523638 I overlayed some of George's data onto one chart. The purple traces are pressure in the breech. The larger curve is an overlay of 3 shots with a pellet and shows good repeatability. The lower curve is a shot without a pellet. In that testing, the pellet generally started to move between 200 and 300 psi. It may be useful to monitor the pellet start of motion at least for a few shots. I realize oscilloscope channels are limited but I was able to track hammer motion and pellet motion on one channel using a resistor divider.

[sb327]

I had some ceramic pressure sensors (400bar) that I got for another project. Wondering what kind of info I could get on my pilot valve, I decided to give it a shot.

I had to make some housings for them and wire them into some instrumentation amplifiers. I set them to output 1v/1000psi (approximately).

I just got a new scope and I’m trying to figure the thing out. I thought I saved the traces to a usb (it said saving was completed) but they didn’t show up. I did take a couple of pictures of the screen though.

I have channel 1 on the pressure side and channel 2 at the slug. Looking at my trace shows the tank side (non regulated gun) pressure acting quite dramatic. I’m wondering if this is my test setup or kind of a ‘ping effect’. The chamber side shows a more sensible expectation.

Any words of wisdom from those who have done this kind of testing? I’m a novice in this area.

I’ll get some pictures of my sensors. Here are the scope pictures. I gotta figure out how to save traces…..

Dave

[WhatUPSbox?]

Very cool, interested in your setup. Looking at your scope spec, it has an external trigger. If that is an input, that could be used to anchor your time trace. Pellet exit is readily available, depending on the gun, hammer launch may be accessible as well.
Great work.

[sb327]

I tie the external trigger of the scope to my arduino signal going to my mosfet for the hammer solenoid. It is a 5v pulse and I pick it up on the rise of the slope.

Here are some more pictures. It’s a crude setup. Second picture is setup for calibrating the instrumentation amps. It’s a hydraulic porta power type pump. The last picture is the inside of the sensor showing how it seals.

Dave

[WhatUPSbox?]

Thanks for posting. Are those the AD620 instrumentation amp boards from Amazon, China, etc? Are you happy with them? I'm looking for an amp for an Endevco sensor I picked up.

[sb327]

That’s the ones. AD620

They’re cheap, that’s all I really know. I’ve never used an instrument amp so I have nothing to compare to.

Dave

[WhatUPSbox?]

Looks like you are set up to collect some interesting data.

[WhatUPSbox?]

It might be worth swapping the sensor locations just to make sure the tank side response stays there. Are those ceramic sensors sensitive to mechanical vibration (if you tap them)? Might be a response to the hammer strike.

[sb327]

That's a good idea. I'll try that.

I got my usb working and now it saves correctly. I also got rid of some noise by attaching a ground to my gun.

Here is the first shot.
4280psi
setting number 4 on my dwell potentiometer
971fps
96gr, 30cal, 24" barrel, 201fpe

first has cursor for voltage (1v=1000psi)
second is for time

Dave

edited to correct pic2

[sb327]

here is shot 2
pressure 4160
setting #7
970fps

Dave

[WhatUPSbox?]

Adding that ground to the gun did a great job on the noise. Can you describe the gun a little bit more? How does the solenoid hammer work? Is it driven in one direction only? What does the dwell period cover? Moving channel 1 to the solenoid to map its timeline?
Channel 2 is on the valve housing? What are the restrictions between the valve and the tank?
Really cool data. There is a rabbit hole for this testing where you suddenly want more channels. 

[sb327]

That’s a lot of info to go over. I have probably muddled Bob and Loyds thread enough here.

This test, for me, was to see how different actual dwell time vs my pulse time, not as much about internal pressures (like Loyd is looking at). I doubt my setup is near accurate enough. Lots of testing left to do.

The gun itself is in one of my build threads here, I’ll have to find it when I get some time and move this discussion to there.

Dave

[WhatUPSbox?]

Thanks

[oldpro]

 What a fascinating and informative thread!~ Thank you everyone.

[rsterne]

Lloyd is still working on the instrumentation, more to come soon!....

Bob

[WhatUPSbox?]

The instrumentation approaches may as interesting as the actual airgun results.