The oil level on the pump should be checked every three months, when the plasma is ONMaintain the oil level between the Ma x and Min levels on the gaugeStandard frequency for changing the oil is appro x imately every 4, 500 hours Be careful when changing oil because the oil may have absorbed dangerous substances. The oil in the rotary pump on the interface side of a 7500 equipped with a hydrofluoric acid resisting introduction system is especially dangerous. DO NOT TOUCH THE OIL WITH BARE HANDS....