<P> Radial piston pumps are used especially for high pressure and relatively small flows . Pressures of up to 650 bar are normal . In fact variable displacement is possible . The pump is designed in such a way that the plungers are connected to a floating ring . This floating ring can be moved horizontally by a control lever & thus causes an eccentricity in the centre of rotation of the plungers . The amount of eccentricity can be controlled to vary the discharge . The suction & discharge can be totally reversed seamlessly by shifting the eccentricity to the opposite side . Hence both quantity & direction can be varied in a radial piston pump, just as in the Swash plate pump . </P> <P> Peristaltic pumps are not generally used for high pressures . </P> <P> Most pumps are working in open systems . The pump draws oil from a reservoir at atmospheric pressure . It is very important that there is no cavitation at the suction side of the pump . For this reason the connection of the suction side of the pump is larger in diameter than the connection of the pressure side . In case of the use of multi-pump assemblies, the suction connection of the pump is often combined . It is preferred to have free flow to the pump (pressure at inlet of pump at least 0.8 bar). The body of the pump is often in open connection with the suction side of the pump . </P> <P> In case of a closed system, both sides of the pump can be at high pressure . The reservoir is often pressurized with 6 - 20 bars boost pressure . For closed loop systems, normally axial piston pumps are used . Because both sides are pressurized, the body of the pump needs a separate leakage connection . </P>

What are the different types of hydraulic pumps