1.Cavitation of centrifugal pumps.
The cavitation phenomenon of centrifugal pump refers to the partial vaporization of the conveyed liquid due to the saturated vapor pressure at the conveying temperature equal to or lower than the pressure at the pump inlet (actually the vane inlet), which causes noise and vibration in the pump. In severe cases, the flow rate, head and efficiency of the pump are significantly reduced. Obviously, cavitation is not allowed to occur in the normal operation of centrifugal pumps. The key to avoiding cavitation is to install the pump at the correct height, especially when conveying volatile liquids with high temperatures.
2.The centrifugal pump is installed at a height of HG.
The permissible vacuum height Hs is the maximum vacuum that can be achieved at the pressure P1 at the inlet of the pump. The actual allowable vacuum height hs value is not a value calculated according to the formula, but a value measured experimentally by the pump manufacturer. This value is attached to the centrifugal pump sample for the user's reference. It should be noted that the Hs value given in the centrifugal pump sample is based on clean water as the working medium, the operating conditions are 20, and the pressure is 1013 The value at 105pa. When the operating conditions and working medium are different, a changeover is required.
1) The centrifugal pump delivers clean water, but the operating conditions are different from the experimental conditions. hs1=hs+(ha-10.33)-(hυ-0.24) It can be converted according to the following formula.
2) When the conditions of the transported liquid and the villain are different from the experimental conditions, two steps of conversion are required: the first step is to determine the Hs1 detected in the pump sample according to the above formula, and the second step is to convert Hs1 into H according to the above formula. s.
2. Centrifugal pump cavitation head δh.
For oil pumps, NP SHΔH is used to calculate the installation height. In other words, NP SHΔH was obtained from the oil pump sample, and its value was also measured with clean water at 20°C. If you are transporting other liquids and need to be calibrated, please refer to the relevant books in detail.
From a safety point of view, the actual installed height of the pump should be less than the calculated value. In addition, when the calculated hg is negative, it means that the suction inlet position of the pump should be lower than the liquid level of the storage tank. Example 2-3: A centrifugal pump finds that the allowable vacuum height hs=5 from the sample7 m。The total resistance of the suction line is known to be 15mh2o with a local atmospheric pressure of 981 104pa, the dynamic pressure head that inhales the liquid in the pipeline is negligible.