Water ring vacuum pump is widely used in the pharmaceutical industry, such as vacuum evaporation, vacuum concentration, vacuum conveyor, vacuum sterilization, vacuum drying, vacuum packaging and vacuum mixed emulsifying process requirement. How to choose the proper vacuum pump reasonably requires some understanding of the principle of various vacuum pumps and the use of methods.
Water ring vacuum pump is water or other liquid as circulating working fluid through the change of pump content volume to achieve the purpose of vacuum extraction. It is impossible to get the inlet pressure lower than the working liquid steam pressure by using liquid ring pump. If the liquid steam pressure is close to the inlet pressure, it will cause cavitation erosion and damage to the pump. For example, at 15 ℃ water vapour pressure of 1.7 x 103 Pa, to avoid cavitation, allowing the minimum inlet pressure of water ring pump is 3.3 x 103 Pa. If the inlet pressure is lower than this value, the media with lower steam pressure, such as kerosene, styrene and ethylene glycol, should be selected.
The gas and liquid mixture from the outlet side of the pump flows into the separator, where the gas and liquid are separated. The gas discharged contains the vapor content equivalent to the vapor pressure of the liquid at the same temperature. Consider the price of working fluid and environmental protection. Operation mode of the main feature is the use of a large number of new liquid decreases, most of the liquid from the separator inside the pump, the pump entrance before joining cold liquid, make the pump inlet temperature constant basically.
If the liquid ring pump pumping toxic or harmful gases, or because of work need to work must use the high price of liquid, the separated in the separator gas can not be empty, should be recycled, while the separated liquid cooling by heat exchanger to pump fluid after normal working temperature, all return to the pump.
Usual operating conditions for water ring vacuum pump pump suction gas temperature is 20 ℃, and the air relative humidity is 70%, the inlet gas pressure of 101.325 kPa, water pump working liquid is 15 ℃. The temperature and steam pressure of working liquid seriously affect the pumping speed. The partial pressure of working liquid in the pumping chamber and the impeller chamber increases with the increase of temperature. Figure 3 shows are pumping gas is 20 ℃ dry air, and water for pump working liquid, in the pumping speed of different temperature 15 ℃ with SLt20 pumping speed SL15.20.
The pumped gas also affects pump performance. If the gas is made up of a mixture of air and steam, condensation can occur when the vapor is in contact with the cold working liquid, and the pumping speed increases. Using 15 ℃ water as working fluid, pumping a certain amount of air and water vapor mixture under different temperature of pumping speed SG15. Delta and 20 ℃ dry air pumping speed Sl15.20. Of course, the ratio of air to water vapor is different, and the effect on the pumping speed is different.
If conveying dry air, due to the heat capacity of small dry air, it was quickly cooled to working liquid temperature, the gas is pumped between the working liquid and the larger the volume of a gas decreases with temperature, the result can make the liquid ring pump pumping speed increase. If the gas is dissolved in the working fluid, it will be released as the working fluid enters the pump inlet side, resulting in a decrease in the pumping speed. The power required by the liquid ring vacuum pump is affected by the working fluid viscosity, density, flow rate and outlet pressure.
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