For those of you who don't want to build a hammer valve out of metal (because metal parts are expensive O_o) this is a PVC alternative I came up with, now it's not perfect, but it's something you could use.
1) Start with 1/4'' nipple or piece of pipe 1'' long
2) Cut 1'' of 1/2'' PVC pipe
3) Sleeve nipple with electrical tape
4) Slide inside pipe and fill both ends with epoxy
* Make sure one end of the nipple and pipe are flush
5) On the flush side, super glue a 1/4'' metal washer
6) Super glue an O-Ring on the washer
* The I.D of the O-Ring should be bigger than the I.D of the 1/4'' washer
7) Plug the end with the washer and O-Ring into an PVC Male-->Female Coupling
8] What you should have
9) With a 1/2'' regular coupling, cut a piece of pipe so when you jam it into one end, both the coupling and the end of the pipe are flush
10) What you should have
11) Get those two pieces, join them
12) What you should have
13) I used these beveled washers
14) This is a 3'' 8/32 bolt with the 1/2'' O.D beveled washer super glued on, this is the stem, remember that O-Ring glued on top of the metal washer? This beveled washer seals that off real nice. =D
15) The 3/8 beveled washer seems to fit very snugly inside the 1/2'' PVC opening
16) Drop in the stem, the rest is common sense
El Producto Finito =]
Drill a hole where that circle is, that will be your port
The I.D of the 3/8 washer is very close to the diameter of the 8/32 bolt so you shouldn't lose that much air, I hope some of you guys find this useful.