Roots pump
Roots pump , also Roots pump , is the name for Roots blower in vacuum technology . It is a rotary lobe pump that uses two symmetrical, counter-rotating rotary lobes to generate a pressure difference in a pressure range of 10 1 to 10 −3 mbar and works on the principle of rotational displacement. Each of the two pistons has the shape of a figure eight and both run off one another in a housing at high speed without touching each other or the housing wall. The distance between the pistons is about 0.1 mm. The scoop is sickle-shaped. The Roots pump requires a backing pump because it cannot cope with pressure differences of any size. It must be installed free of tension and as horizontally as possible.
The pumping process can be divided into four phases: In phase I, the gas penetrates the volume facing the recipient. During phase II, the volume is steadily increased until a sickle-shaped suction chamber is separated from the gas inlet side in phase III. In phase IV, the gas gains access to the pump chamber on the discharge side. The gas inside is compressed by the inflowing gas and expelled as the piston continues to move. At high speeds, despite the losses at the gaps (low conductance), a high pumping speed is achieved. The speed is limited by the centrifugal forces acting on the piston material.
The advantage of this pump is that there is no lubrication in the pump chamber. This is an important prerequisite for backing pumps for UHV systems. Due to the flow resistance and the different temperature coefficients of the pistons and the housing, the Roots piston pump itself requires a backing pump.
