A brief discussion on the comparison of characteristics between screw vacuum pumps and liquid ring vacuum pumps

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Pump-type dry screw vacuum pumps and liquid (water) ring vacuum pumps: Working principle – Two rotors and the casing together form several chambers through which gas is compressed. The rotors rotate inward in opposite directions; these gas chambers move regularly from the inlet to the outlet side of the pump, allowing the gas to be transported out in a manner that minimizes turbulence, thereby enabling the evacuation of process gases. Driven by the liquid ring, the gas drawn in at the inlet mixes with the liquid ring, and suction, compression, and exhaust are achieved through changes in the volume of the pump chamber. A screw vacuum pump consists of components such as rotors, a casing, a gearbox, and a water cooling jacket. A liquid ring vacuum pump, on the other hand, comprises elements like a pump shaft, impellers, partitions, a casing, a vapor-liquid separation tank, heat exchangers, and pipeline pumps. Vacuum level – Regardless of the vapor content in the process gas, screw vacuum pumps can maintain a high level of vacuum (suction pressure range: atmospheric pressure to 1 Torr). Due to temperature variations of the working fluid in summer, the vacuum level may become unstable; in such cases, the suction pressure ranges from 60 Torr. Limit pressures – The maximum pressure for a single screw vacuum pump is between 5 and 50 Pa, while that for a single liquid ring pump is around 3300 Pa. This pressure depends on the type of working fluid and its temperature； To achieve a high level of ultimate vacuum, it is necessary to use it in combination with a Roots pump. It allows for operation at high pressures (up to 105 Pa, i.e., atmospheric pressure), with an evacuation rate of up to 2700 cubic feet per hour; thus, it has a wide range of operational capabilities. It can maintain a high evacuation rate from atmospheric pressure down to 1 Torr. The evacuation rate varies significantly starting from atmospheric pressure, and below 50 Torr, the evacuation rate of the liquid ring vacuum pump drops considerably. Moreover, prolonged operation at low pressures can lead to cavitation. The jacket of the vacuum pump requires a small amount of cooling water to dissipate the heat generated during compression, and this cooling water can be reused provided it remains clean. The working medium for a liquid ring vacuum pump is water or some other liquid substance, and the cost of processing such working fluids is relatively high. The consumption of fluids like water is also significant. Under the same suction pressure conditions, its power consumption is lower compared to other types of vacuum pumps ； The power consumption remains relatively constant; it varies depending on factors such as coolant temperature, flow rate, type of process gas, and vacuum level. Oil and gas recovery systems require simple daily maintenance, are easy to maintain, have few wear-prone components, and thus incur low repair costs ； It has a compact design and occupies little space; it consumes little water. However, its operation is complex, and the maintenance costs are high – the working fluid needs to be replenished or replaced regularly, as well as the pipes carrying the working fluid. Its price is high, but it represents good value for money due to the one-time investment required. At a lower level: Solvent recovery is applied in fields such as petroleum and chemical industries, machinery, mining, light industry, pharmaceuticals, and food processing – areas that include solvent recovery using vacuum drying, chemical manufacturing, oil and gas recovery, as well as aviation and aerospace. To achieve a recovery efficiency of over 98%, it is sufficient to install a solvent recovery device at the exhaust port of the screw pump. Liquid ring vacuum pumps, on the other hand, require an additional working fluid medium, along with accessories such as vapor-liquid separation tanks, pipeline pumps, and heat exchangers