Reversing Valve for Fluid Compressors — why the pump goes fwoosh-chunk

Steam drives the top piston; the rod drives the air piston below. At each stroke end the reversing rod trips the pilot — and steam SNAPS the valves over.

Amber glow = live steam · dim blue = exhausting · light dots = air. Thompson's fix: the stroke only triggers the reversal — steam pressure completes it, so the pump can never stall half-thrown.