A relief valve is provided to prevent the lubrication pump from being overloaded. With unloading function, the oil pump can unload the oil pressure of the main line after it stops working to ensure that the next cycle of the quantitative distributor works normally, mainly used in grease lubrication systems. The oil pump can be equipped with a pressure switch (normally open AC220V/2A DC36/2A) to monitor the lubrication system main road breakage, loss of pressure or oil tank shortage. A digital display controller can be configured. Matching distributor: various grease distributors. Medium used: thin oil or grease 00#-0# lithium ester.