Measurement of pumping rate of Roots vacuum pump
The constant pressure method is used to measure the pumping rate of Roots vacuum pump. The inlet of the pump is directly connected with the experimental cover, and the outlet of the pump is connected with the front oil seal mechanical pump. A vacuum gauge is set at the inlet and outlet to measure the pressure. The flowmeter is connected with the experimental cover through the regulating needle valve. After starting the vacuum pump and reaching the stable working condition, the measurement can be carried out. The pumping rate should be measured from the appropriate value close to the limit vacuum until the allowable inlet pressure of the pump is nearly stopped. At least four points in each order of magnitude should be measured, and their dispersion should be in accordance with the ratio of 1,2,5,7, such as 1xl0-2, 2x10-2, In the measurement process, after adjusting the needle valve to a certain pressure, the pressure data can be recorded after at least 3min after the pressure reading on the vacuum gauge is stable. If the pressure is changed, the uniform value of pressure in the measurement process should be selected.
The structural dimensions of the test cover are specified in the Ministry of standards (jb1875-73), and its structure is shown in Figure 7-2. The inner diameter D of the test cover should be equal to the inlet diameter of the pump.
In the equipment for measuring the pumping rate, the vacuum gauge used should be seat type compact vacuum gauge and oil U-type vacuum gauge, and calibrated by the compact vacuum gauge with an accuracy of more than 10%. The air intake plane of the vacuum gauge should be parallel to the air flow direction. It is necessary to have the second-order accuracy in the measurement scale for the flowmeter used in the flow measurement.
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