What you will need to do this effectively:
-something to test presser with (I used the pressure gauge attached to my LS)
-and airsoft BB
-some fairly strong smallish springs, I just got some industrial strength one at Ace
-1/4" OD, 1/8" ID vinyl tubing
-barbed coupling (optional)
(barbed fittings not shown)
I'm not going to do a full step-by-step write up, as the pictures should really explain everything. I'm more just going to go into some basic concepts.
First, here's and equation that Zeke came up for me a while back, to figure out the required spring constant and pre-load on the spring for a certain PSI (I'm fairly certain that the only units in this equation are inches, so don't worry about any conversions):
(spring constant)(pre-load in inches) = (psi)(area of sealer)
Now if we are focused a certain PSI, we set it up like this:
(psi) = ((springconstant)(pre-load)) / (area of sealer)
If you're using my set-up, you can assign 1/8 for (area of sealer), as that much of the BB will be sealing on the vinyl tubing.
Now, I never actually got around to using this formula, I just bought some springs and tried them out in a not fully glued together valve. I highly recommend this, as guessing and checking is far more reliable in this case. The formula comes into play if you're ordering springs online.
Here are some pics now:
Now, here's how you're gonna get the PSI you want. You're going to NEED a pressure gauge at your disposal.
Mutilate the pen to get the tube. Glue in a segment of tubing on one end. If you're using a barbed fitting, it doesn't need to be very long. This will be your air input end.
Now put in the BB, and then the spring. Put a segment of vinyl tubing in last, and compress the spring a bit. DO NOT glue the tubing in on this end, or you won't be able to find the desired pressure. Hook up the air input to a tee, with the other two airways connected to your pressure gauge and pump.
Pressurize the valve. Hopefully the pen tube will grip the tubing well enough that it won't shoot out or leak too much when you pressurize the valve. It'll leak a little, but it'll still work for the testing phase. The pressure on the valve will spike, and then jump down. Wait until you don't hear/feel (by plugging the end with your thumb) any more air exiting the valve. Record the pressure shown on the gauge. Rinse and repeat, but adjust the tubing in the air outlet for different pressure levels. Here's a pic to help you with your testing:
Once you get the pressure you want, mark how far the vinyl tubing is into the pen body. Apply glue, and put it to the marked length. There you go, you're done.
The valve in this write-up releases air at about 45 PSI. It was made for use on a RSCB'd 4B, as shown below.
Now you can loan your air guns out without having to worry.
What do y'all think?
Scroll down for update!
Edited by TantumBull, 17 October 2009 - 01:12 PM.