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Working principle of water ring vacuum pump/liquid ring vacuum pump The water ring vacuum pump (abbreviated as water ring pump) is a type of rough vacuum pump; the ultimate vacuum it can achieve is 2000–4000 Pa, and this value can be increased to 270–670 Pa when used in series with an atmospheric ejector. Water ring pumps can also be used as compressors, known as water ring compressors; they are low-pressure compressors with a pressure range of 1–2×105 Pa gauge pressure. Water ring pumps were initially used as self-priming pumps, and later came to be employed in many industrial sectors such as petroleum, chemicals, machinery, mining, light industry, pharmaceuticals, and food processing. Water ring pumps are widely used in many industrial production processes, such as vacuum filtration, vacuum water pumping, vacuum feeding, vacuum evaporation, vacuum concentration, vacuum rehumidification, and vacuum degassing. Due to the rapid advancement of vacuum application technology, water ring pumps have always been highly regarded for achieving rough vacuums. Since the gas compression in a water ring pump is isothermal, it can be used to pump flammable and explosive gases, as well as gases containing dust or moisture; therefore, water ring pumps are being used more and more often. An appropriate amount of water is placed in the pump body as the working fluid. As the impeller rotates clockwise as shown in the diagram, water is thrown outward by the impeller; due to centrifugal force, the water forms a closed ring of approximately uniform thickness, whose shape is determined by that of the pump chamber. The inner surface of the lower part of the water ring is in exact tangency with the impeller hub, while the inner surface of the upper part of the water ring is in contact with the tips of the blades (in fact, the blades extend to a certain depth within the water ring). At this point, a crescent-shaped space is formed between the impeller hub and the water ring, and this space is further divided by the impeller into several small chambers, one for each blade. If 0° at the lower part of the impeller is taken as the starting point, then when the impeller has rotated 180°, the volume of the small chamber increases and it becomes connected to the suction port on the end face; at this point, gas is drawn in. Once suction is complete, the small chamber becomes separated from the suction port ； As the impeller continues to rotate, the small chamber becomes smaller, causing the gas to be compressed ； When the small chamber is connected to the exhaust port, the gas is expelled outside the pump. In summary, a water ring pump relies on changes in the volume of its pumping chamber to achieve suction, compression, and exhaust, and therefore it belongs to the category of variable-volume vacuum pumps. Working principle of the Roots pump: Inside the pump chamber, there are two rotor elements in an “8” shape, which are mounted perpendicularly on a pair of parallel shafts. They are driven by a pair of gears with a gear ratio of 1 to rotate synchronously in opposite directions. A certain gap is maintained between the rotors and between the rotors and the inner wall of the pump casing, which enables operation at high speeds. Since a Roots pump is a vacuum pump without internal compression and typically has a very low compression ratio, high- and medium-vacuum pumps require a pre-pump. The ultimate vacuum of a Roots pump depends not only on the pump’s own structure and manufacturing precision but also on the ultimate vacuum of the pre-pump. To increase the ultimate vacuum of the pump, Roots pumps can be used in series. The working principle of a Roots pump is similar to that of a Roots blower. Due to the continuous rotation of the rotor, the gas to be pumped is drawn in from the inlet into the space v0 between the rotor and the pump casing, and then discharged through the outlet. Since the v0 space is completely sealed after inhalation, the gas in the pump chamber does not compress or expand. However, when the top of the rotor passes over the edge of the exhaust port and space v0 becomes connected to the exhaust side, the higher gas pressure on the exhaust side causes some gas to flow back into space v0, resulting in a sudden increase in gas pressure. As the rotor continues to rotate, the gas is expelled from the pump. Working principle of the vane vacuum pump The vane vacuum pump (abbreviated as vane pump) is a oil-sealed mechanical vacuum pump. Its operating pressure range is 101325~1.33×10-2 (Pa), classifying it as a low vacuum pump. It can be used alone or as a pre-pump for other high-vacuum pumps or ultra-high-vacuum pumps. It has been widely applied in production and research sectors such as metallurgy, machinery, military industry, electronics, chemicals, light industry, petroleum, and pharmaceuticals. Vane pumps can remove dry gases from sealed containers; if equipped with a gas trap, they can also remove a certain amount of condensable gases. However, it is not suitable for pumping gases with high oxygen content, those that are corrosive to metals, those that react chemically with pump oil, or gases containing particulate dust. The rotary vane pump is one of the most fundamental vacuum generation devices in vacuum technology. Vane pumps are mostly small and medium-sized pumps. Vane pumps come in single-stage and double-stage types. The so-called two-stage configuration involves connecting two single-stage pumps in series structurally. They are generally designed as two-stage systems to achieve a higher vacuum level. The relationship between the pumping speed of a rotary vane pump and the inlet pressure is specified as follows: at inlet pressures of 1333 Pa, 1.33 Pa, and 1.33×10^-1 Pa, its pumping speed must be no less than 95%, 50%, and 20% of the pump’s nominal pumping speed, respectively. A rotary vane pump is mainly composed of a pump body, rotor, vanes, end caps, springs, etc. A rotor is installed eccentrically within the chamber of the vane pump; the outer surface of the rotor is in contact with the inner surface of the pump chamber (with a very small gap between them), and two vanes equipped with springs are placed within the rotor slots. During rotation, centrifugal force and the tension of the spring keep the tip of the rotor in contact with the inner wall of the pump chamber, and the rotation of the rotor causes the rotor to slide along the inner wall of the pump chamber. The two vanes divide the crescent-shaped space enclosed by the rotor, the pump chamber, and the two end caps into three sections: A, B, and C. As the rotor rotates in the direction indicated by the arrow, the volume of section A, which is in communication with the suction port, gradually increases, indicating that suction is taking place. Meanwhile, the volume of space C connected to the exhaust port is gradually decreasing, and it is in the exhaust process. The volume of the centered space B is also gradually decreasing; it is in a compression process. As the volume of space A gradually increases (i.e., expands), the gas pressure decreases. The external gas pressure at the pump inlet is higher than the pressure inside space A, so the gas is drawn in. When space A is isolated from the intake port, that is, when it moves to the position of space B, the gas begins to be compressed, the volume gradually decreases, and eventually it becomes connected to the exhaust port. When the compressed gas exceeds the exhaust pressure, the exhaust valve is pushed open by the compressed gas, allowing the gas to pass through the oil layer in the tank and be released into the atmosphere. Continuous operation of the pump achieves the purpose of continuous pumping. If the exhaust gas passes through the airway to another stage (the low vacuum stage), is drawn away by that stage, and then compressed by it before being released into the atmosphere, this constitutes a two-stage pump. At this point, the total compression ratio is handled by two stages, thereby improving the ultimate vacuum level.