Abstract: An automatic lubrication system where grease is dispensed to injectors from a pump having a grease piston (42) reciprocated by a connecting rod from an oil piston (43) driven by alternating hydraulic pressure, is provided with air purge valves (41) associated with each injector. The air purge valves detect abnormal operation of the piston movement due to air in the grease by way of indicators (45) and (46) communicating with chambers in the pump, and open the air purge valve to dump air laden grease into a recovery reservoir (48). A sensor in the air purge valve warns the operator of purge valve operation, alerting the operator to a possible system malfunction.