I am working on a GE 25 ton, for the first time in probably 20+ years had the compressor making it's own pressure in the tanks. Others plumbed in the new compressor and I think they forgot some parts. AFAIK there should be a pilot valve between the compressor unloader and tank, they have plumbed the unloader valves right to the tank pressure, however it looks that maybe some compressors have the pilot valve built in?

Does anyone have a picture of the pilot valve? Maybe even a part #?

How old is the engine? We have a 23 ton GE, but it was built in 1941. I have the Army manual for it, that someone here was nice enough to send us.

You should have a NS-16 compressor governor connected to the main resevoir. The compressor unloader should then be plumbed into the NS-16s unloader port.