Most Anti G Valves will operate and look very similar to this one...
The pressure inlet is the air tapped from the engine compressor,through a pressure reducing valve and into the anti g valve where it will be regulated between zeroish and 10 psi - controlled by the weight operating against its return spring.The press to test button usually operates directly onto the weight so you push down on it to inflate suit and when you release it the suit should deflate.