Use and precautions for water ring vacuum pumps

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This post was last edited by lovestory on 2012-1-12 at 15:02. In water ring vacuum pumps, water is generally used as the working fluid. The energy acting on the rotor impeller is absorbed by the liquid and transferred to the compressed gas, which results in an increase in the temperature of the water ring. Some of the water in the water ring is compressed together with the gas and discharged outside the pump. Most of the heat generated during compression is removed. Therefore, it is necessary to continuously supply fresh water in order to maintain a constant operating temperature for the water ring pump. In most water ring vacuum pumps, the operating temperature is around 15–20°C, depending on the temperature of the water supplied. In fact, the ultimate pressure of a water ring pump is not that important, as different liquids will experience cavitation at pressures below 50–60 hPa, leading to damage to the pump’s components. When the pump approaches its limit pressure, the pumping speed is very low, and the water at the pump inlet begins to boil. When it reaches the pump’s outlet, the bubbles formed begin to burst. This will result in significant noise, and components such as the pump’s drive wheel and pump chamber will be gradually damaged. This phenomenon is commonly referred to as cavitation. Once cavitation occurs, a small amount of fresh air must be introduced through a valve. In this case, a small hole is made in the inlet pipe to allow for the quantitative addition of fresh material; if a gas injector is used, cavitation will not occur. Single-stage water ring pumps are suitable only for pressure ranges of 130–1013 kPa, with a compression ratio of 1:7. When the inlet pressure is below 130 kPa, a two-stage water ring pump is recommended. In a two-stage pump, the two pump chambers are connected in series, with a volume ratio of the working chambers of approximately 2.5:1. The ultimate pressure of a two-stage water ring pump depends on the vapor pressure of water. Assuming that the vapor pressure of water at the pump’s operating temperature is pH2O, the inlet pressure is pA, and the geometric pumping speed is Sth, experience shows that when the pressure is below 130 hPa, the effective pumping speed of the pump is SA = Sth(1-pH2O/pA). Given the low vapor pressure of oil, two-stage liquid ring pumps can also be used with oil as the working fluid, thereby achieving a lower ultimate pressure. However, when it is necessary to remove a large amount of water vapor, especially in cases of rough pumping and essential oil extraction, oil is rarely used as the pumping fluid in liquid ring pumps because the oil tends to absorb water and form an emulsion. If oil is used as the pumping fluid, the pump must also be equipped with an oil cooling device to dissipate the heat of compression. Three-stage or multi-stage liquid ring pumps are rarely used. However, liquid ring pumps are often used in series with gas ejectors, water ejectors, and Roots pumps.