Working principle: 1. when the oil pump work output lubricating oil when the oil separator internal piston cavity oil storage. 2. at this time the rod extends, indicating normal oil storage. 3. when the oil pump stop working, the oil pump unpressure. 4. the oil in the piston cavity, by the spring action escort to the lubrication point, this process indicates the rod reset. 5. complete the whole action indicates that the oil is normal.