SpudFiles

I just installed a onboard air compressor on my jeep and I'm building a coax to test it out. I have my golf ball barrel(48" sch80/sdr21) and I'm stumped on what size I should make my chamber out of 3 or 4 inch? Three inch will have less expensive fittings but less volume for air, with 4 inch just the opposite, though possible easily made piston just a three inch endcap and some rubber. Anybodies thoughs?

Use 4 inch. It will cost more but the end results will be wonderful compared to a 3 inch chamber.

Thats what I thought, Now just to find some on the cheap, and anybody know about the using a 3inch endcap as a piston thing I remember someone saying that they used one. Any idea?

A 3 inch endcap piston may have difficulty going into a 4 pipe. If that is the case you can construct a 3 inch piston using this thread.

Hi,

It could have been me with the endcap as a piston, but I use European, metric fittings.

Anyway, try see if you can find an endcap that will fit. Or, a plug with a piece of pipe glued on it. They make great pistons.

Hubb, why would the end cap need to go into a 4 inch pipe? It could also be put into the tee directly. But OK you will need to carefully file down the "lip" in there to make the ID exactly 4 inches everywhere.

A 4 inch valve, wow... I feel slightly compelled to construct a 110mm valve, just to beat you. But I have no Jeep and no compressor

If it only a few mm

Regards
Soren

A 3" end cap doesn't fit in 4" pipe, I know, well not here anyway in metric land.

@dongfang - he was wanting to build a coaxial so I would assume he was wanting the piston in the pipe. From the measurements I have, a 3" end cap is 4" in diameter while the inside diameter of 4" SCH 40 PVC is 3.5 inches.

I could put a 3 inch cap on the lathe and cut it down if there is enouth material, If not I can use those thin test caps, just cut the rim off and stack some up and bolt together. It what I used for my pingpong gun.

Hi Hubb*,

Aah I missed the coaxial part.

Regards
Soren

In the USA at least, a three inch sch. 40 pvc end cap fits inside 4" sch 40 pvc pipe with about a millimeter of a gap all the way around. I know this for sure, i read this thread and thought that that was the case but others had said otherwise, so i just went and tried it. and so having put a three inch end cap inside four inch pipe less than a minute ago, i can say for certain that it fits. if it doesn't then your fittings are different from mine somehow, but mine are regular sch 40 pressure rated pipe and end cap, just the usual stuff from home depot.