I've got the red one from Robart and it works. However, trying to trim the needle valves was a pain. So I fixed them in place and put Loctite on the thread and then used some SMC one-touch fittings w/ a adjustible knob to better control the air flow. Anyway, check the side load on the shaft and see if you can keep the air from leaking out. Try it without the servo attached and double check the tube input/outputs.