A valve assembly includes a block with a chamber formed therein and a port for accessing the chamber. A fluid inlet passage and a fluid exhaust passage are formed through the block and communicate with the port. A main valve includes a head which is reciprocated into and out of engagement with a lower valve seat formed on a portion of the port. An auxiliary valve includes a head which is reciprocated through the port between a first position below the port and a second position above the port. A hollow cylindrical valve includes a central passage therethrough for fluid flow, and is disposed for reciprocating movement into and out of engagement with an upper valve seat formed on a portion of the port, the cylindrical valve closing the inlet passage when moved to the engaged position. The cylindrical valve passage is in communication with the exhaust passage throughout its movement. Apparatus is provided for sequentially moving each of the main valve, auxiliary valve, and cylindrical valve to sequentially introduce air from the inlet passage through the port and into the chamber, close the port from all fluid flow, and exhaust fluid from the chamber through the port and through the exhaust passage.