[AndyH]

You can also try getting a pipe plug and drilling a small hole in the plug and screw it in the exhaust port of the air valve. This will slow the exhaust and therefore slow the piston. It works well and you simply keep drilling out the hole till the desired piston speed is achieved. You can also get adjustable flow control valves. I like the pipe plug trick because once it is correct it can not be adjusted and messed up. I use this in industrial applications all the time.