The two-stage vane pump is made up of two ordinary pressure single-stage vane pumps E and one pump body connected in series on the oil circuit. The rotors of two single-stage vane pumps are mounted on the same transmission. On the shaft, a two-stage pump is formed. The first stage pump draws oil from the fuel tank, the oil outlet is connected to the inlet of the second stage pump, and the output oil of the second stage pump is sent to the working system. Because the structural dimensions of the two pumps are impossible To do exactly the same, the displacement of each single-stage gear pump can not be exactly equal. For example, the displacement of the second-stage pump per revolution is greater than that of the first-stage pump, and the suction pressure of the second-stage pump is the first-stage pump. The outlet pressure is reduced, and the inlet and outlet pressure of the second-stage pump is increased; on the contrary, the load of the first-stage pump is increased. For this reason, the ratio of the installation area between the two pumps is 1: The proportional pressure valve (load balancing valve) of 2 can make the pressure difference between the inlet and outlet of the two single pumps equal, that is, the pressure load of the pump is equal, and the proportional pressure valve functions as automatic pressure distribution or load balancing. And the second stage pump output oil passage is respectively connected to the left and right end faces of the balance valve via the pipes 1 and 2, and is slipped. The area ratio of the spool is Ai: A2 = 2:1. If the flow rate of the first stage pump is greater than that of the second stage pump, Pi increases, so that p1:p2>1:2, so pIAl>p2A2, the spool is Push right, the excess oil from the first stage pump flows back from the part 1 through the valve opening to the inlet line of the first stage pump, so that the load of the two pumps is balanced; if the flow rate of the second stage pump is greater than that of the first stage pump The oil pressure pl is lowered, so that the piAl <p2A2, the balance valve spool is pushed to the left, and part of the oil at the outlet of the second stage pump flows from the tube 2 through the valve opening to the inlet of the second stage pump to obtain balance; If the flow rates of the two pumps are equal, the valve ports on both sides of the balance valve are closed. Two single-stage vane pumps are assembled in a pump body on the oil circuit, 夕 = Δpi + Ap2 , Qi = Q2 = Qo