Most of the Rexroth oil pumps are positive displacement pumps. The characteristic of this type of pump is to achieve oil suction and pressure through the volume change of a closed space. When the closed volume increases from small to large, oil will be absorbed. On the contrary, from large to small It will press oil when Rexroth plunger pump is a more obvious positive displacement pump, just like a needle, the internal volume is changed by the movement of the plunger.