The circumferential piston pump is a rotary flow positive displacement pump design, which is well-suited for a wide range of applications due to its relatively low speed and inlet pressure requirements and large cavities. These designs have only two moving parts within the fluid chamber and hence have proven reliable. There is no sealing contact between the piston surfaces, which distinguishes this design from gear and screw pumps. External timing gears synchronize the circumferential pistons. As the circumferential piston rotates on the inlet side, the expanding volume draws the liquid into the pump. The liquid is forced out the discharge port by the collapsing cavity on the discharge side.