So, without further ado, I present the B.U.F.F. (Credit to Sharvil for the name, haha)
1 1/4" PVC
1 1/4" PVC tee
1 1/4" PVC coupler
1 1/4" to 3/4" PVC bushing (2)
3/4" to 1/2" PVC bushing (2)
1 1/4" PVC cap
3/4" PVC cap (3)
3/4" to 1/2" CPVC bushing
3/4" PVC cross
3/4" PVC plug
1/8" ID tubing to 1/4" NPT adapter (McMaster #5116k302)
Check valve (McMaster #2987K21)
OPV (McMaster #50265K23)
Bell Dual Action Bike Frame pump
Total: about $30, including the pump.
Now for construction!
NOTE: There is a new method for piston construction HERE that's much simpler. Would be easy to drill two holes and add the check valve to the rear. Plus, it seems to seal better.
First, we make the piston. Take two 3/4" endcaps (the flat kind you find at smaller stores, like Ace, True Value, etc) and cut them roughly in half. Take one endcap, drill a small hole, and install a McMaster check valve, with airflow going towards the interior of the cap. You will then mount the pieces on a roughly 2.5" piece of 3/4" PVC, as shown. The rings must be reversed in position, so that the flat, uncut sides face the ends of the piston. Use you super glue or other favored epoxy to put everything in place. Cut/drill a tiny hole in the side opposite the check valve, to bleed air into the chamber. Also put a craft foam circle at that end. Finally, Take your o-rings and slip them on. The piston is complete.
Now, the chamber: You need ~3 inches of 1 1/4" PVC. To compact my design, I sanded one end with my dremel until it was thin enough to stick past the "hump" of the PVC tee, so to speak. This was purely for compacting the design, and is not necessary, as the wall is thin enough that, without care, you can crack it, etc.
On the other end, put in a 1 1/4" to 3/4" bushing, with another bushing to reduce to 1/2". 1 1/4" to 1/2" Bushings DO EXIST, but don't seem to be very common at hardware stores, at least not in slip couplers (There were ones made for having threaded 1/2" PVC, I just decided not to use them). Hammer some 1/2" CPVC into 1/2" PVC, and place in the chamber. Place a 1/2" to 3/4" bushing at the end of that, to provide a flat sealing surface. Slide in your piston, and look at the marvelous seal!
Please note that you should use silicon grease on your o-rings and all that jazz. It helps.
Now to cap the chamber: This is where you have to take some guesswork. You only want the piston to have a small motion (1/4" at most), so you'll have to adjust the fit accordingly.
Using another 3/4" endcap, place (but not glue) in another 1 1/4" bushing. (I recommend just stepping down to 3/4" for the bushing, as you'll see later). Line it up to be flush with your 1 1/4" pipe, and test the piston movement manually with a pencil or something. Shave off the open end of the cap until you get the desired fit, then epoxy into place. put a craft foam bumper on the end of that, to help make the thing last. Finally, drill/dremel a bleed hole in the middle so air can actually pass. Now you can throw on a 1 1/4" coupler and connect everything. The chamber is complete.
Edited by Buffdaddy, 20 August 2011 - 10:57 PM.