How Does a Roots Vacuum Pump Work?

An appropriate amount of water is placed in the pump chamber as the working fluid. When the impeller rotates clockwise as shown in the figure, the water is thrown outwards by the impeller. Due to the effect of centrifugal force, the water forms an approximately uniform-thickness closed circular ring determined by the shape of the pump chamber. The inner surface of the lower part of the water ring is exactly tangent to the hub of the impeller, and the inner surface of the upper part of the water ring is exactly in contact with the top of the blade (in fact, the blade has a certain insertion depth within the water ring). At this time, a crescent-shaped space is formed between the inner interface of the impeller hub and the water ring. This space is divided into several small cavities equal to the number of blades by the impeller blades. If the lower part of the impeller at 0° is taken as the starting point, then the volume of the small cavity decreases as the impeller rotates 180°, and it is in communication with the suction port on the end face. At this time, the gas is sucked in. When the suction ends, the small cavity is isolated from the suction port. When the impeller continues to rotate, the small cavity becomes smaller, causing the gas to be compressed. When the small cavity is in communication with the exhaust port, the gas is discharged outside the pump. Once the impeller rotates one full circle, the space (small cavity) between the blades (small cavities) takes in and exhausts gas once. The several small cavities work continuously, and this process repeats, allowing the pump to continuously suction or pressurize the gas.