Abstract: A vane type pump suitable for a hydraulic system comprises passages communicating with the underside of the vanes in the inlet quadrant with the surrounding of the drive shaft and passages communicating the underside of the vanes in the discharge quadrant with the discharge chamber, thereby the underside of the vanes can act as a set of additional little pumps while being ineffective at zero pressure. The undervane pressure in the inlet quadrant can be tested and adjusted at any time during the operation by a manometer and an auxiliary valve. The vane type pump in accordance with the present invention is adapted to various viscosities of fluid such as 1-38 cst, 50.degree. C., and it is possible to work at negative pressure without keeping the reservoir a certain relative height and without replacing the inner component. The pump works at a high volumetric efficiency and total efficiency all the time.