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Usually liquid ring vacuum pump performance curve is divided into shaft power curve and gas curve. (1) Shaft power curve Liquid ring vacuum pump operates at a certain rotational speed, uses normal temperature water as working fluid, and forms different suction vacuum through inlet throttling method to measure shaft power corresponding to suction vacuum point (usually indicated by suction absolute pressure). Then take the suction vacuum point as the abscissa and the shaft power as the ordinate and connect the shaft power under different vacuum points into a curve under the absolute vacuum range of 0-1013 hPa. (2) Extraction volume curve The liquid ring vacuum pump is operated at a certain speed, taking the vacuum point as the abscissa and the suction amount as the ordinate, and connecting the suction amount under different vacuum points into a curve under the absolute pressure range of 0-1013 hPa. According to industry habit, the volume of gas in the sample curve refers to the volume flow of the suction saturated air under the specified conditions (working water temperature of 15 ℃ and air temperature of 20 ℃). ③ liquid ring pump efficiency liquid ring pump products generally do not directly indicate the pump efficiency curve, but can be calculated as follows: Where n-pump efficiency; Pa - pump shaft power, kW; Pi. Pump isothermal compression power, kW. Pis a 38.37plV lg (pz / Pl) where P1 - pump inlet gas absolute pressure, MPa; V - pump inlet pressure pl, the amount of gas in the inhalation state, m3 / min; P2-- pump outlet Absolute gas pressure, MPa. In the selection, in order to more intuitive comparison of different types of pumps operating efficiency, you can also use the pump at the operating point of the exhaust per hour divided by the corresponding point of shaft power, in units of ms / (kW · h), the greater the value , The higher the operating efficiency of the pump. ④ Dry and wet air extraction curve The vacuum curve of the vacuum pump is tested with water as the liquid. During the test, the air volume measured in the atmospheric environment is regarded as dry air due to throttling through the orifice plate. In the wet test The amount of exhaust measured on the stage is referred to as the amount of saturated exhaust of the vacuum pump. Liquid ring pump products on the market, the gas curve is generally expressed in the suction pump capacity under saturation, referred to as moisture. V = Vo [p / (p-pl)] (2-33) Where V-- saturated extraction, ITl3 / min; V0 - dry air extraction, rn3 / rain; p- - point of absolute pressure, hPa; P1 - corresponding to the working water temperature under the saturated vapor pressure, hPa. 2. Vacuum pump selection Vacuum pump selection, the following situations: ①In actual conditions, temperature, operating temperature and product performance curve of the test conditions are inconsistent, the need for temperature and water temperature correction. The operating point of the required amount of exhaust gas amended to the amount of gas under the conditions specified in the sample, and then selection. Where V - vacuum pump gas volume under specified conditions (working temperature l5 ℃, inlet temperature 20 ℃, available in product samples), m3 / min; Vs - the amount of gas required for the actual conditions, rn3 / rain; Ka - temperature correction factor; Kw - water temperature correction factor. Plt - the actual working water temperature corresponding to the saturated vapor pressure, hPa; Tw - the actual working conditions of working water supply temperature, ℃; Ta - the actual working conditions was pumping gas temperature, ℃. In the actual application process, the water temperature and the air temperature may also be corrected by the relevant and verified empirical pupil line. If other liquids are used as the working solution, the correction can be made according to the application experience of different working solutions. ② The actual working conditions and the conditions prescribed exactly the same or after the water temperature, temperature and amended conditions consistent with the provisions of the product samples can be directly selected. If the product performance curve does not correspond to the speed, can be used to select the insertion method. Changes in speed and gas volume is proportional to the change in shaft power and speed is proportional to the square of change. V1 - need to use the amount of pumping; curse - sample speed can be found; V - performance curve at the speed of n pumping volume; / - / 1 - insert speed; Power; P - 轴 speed under the shaft power. (3) When the gas to be drawn is dry air and the performance curve of the product sample is saturated air, the dry and wet gas conversion will be carried out according to the formula (2-33). ④ In the following two conditions, it is recommended that the equipment manufacturer choose according to the application experience: the difference between the characteristics of the drawn-in gas and the air at room temperature is large; the density, viscosity and vaporization pressure of the working fluid are greatly different from the normal temperature water, Concentrated sulfuric acid to do the working fluid.