【Daily Question: Pump Equipment】Short Answer Question, 3/8/2019
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The last edit to this post was made by 3983596_FPPZ on 2019-3-8 at 09:20, with the file bk14.jpg. The operating conditions of the device are as follows: the medium is LPG (liquefied petroleum gas); at the rated flow rate, the pressure at the pump inlet is 0.94 MPa (G), and the device operates in reverse flow mode. The operating temperature is 25 degrees Celsius, at which the vaporization pressure of LPG is also 0.94 MPa (A). A centrifugal pump with a net positive suction head of 3.4 m. Without considering the impact of temperature changes, is this pump operating properly? Please provide the calculation process. Answer: It can be used normally. The NPSHA of the device is equal to the inlet pressure (relative) + atmospheric pressure (absolute) – vaporization pressure (absolute), and this value is greater than the pump’s NPSHR plus 0.6 (as a safety margin). 0.94 + 0.1 – 0.94 = 0.1 (approximately 10 meters of water column), and 10 > 3.4 + 0.6 = 4
It should be possible, after all, there is a gauge pressure of one atmosphere, which translates to a significant difference in height in meters. Piping resistance isn’t mentioned, and it generally isn’t very high either. If the pipe diameter at the inlet is too small, it is possible that excessive resistance will occur, leading to pump cavitation.
Sure. Without considering friction, the pump inlet pressure (G) + atmospheric pressure – the vapor pressure of the medium at that temperature (A) = effective net positive suction head. Approximately 10 meters of water column is greater than 3.4 m + 0.5 M
It can be used normally; the NPSHA of the device is equal to inlet pressure (relative) + atmospheric pressure (absolute) – vaporization pressure (absolute) > pump’s NPSHR + 0.6 (safety margin). 0.94 + 0.1 – 0.94 = 0.1 (approximately 10 meters of water column), and 10 > 3.4 + 0.6 = 4
Yes, 0.1+0.94-0.034-0.94>0
It can be used normally; the absolute pressure at the pump inlet, as calculated, is 1.04 MPa, which is higher than the vaporization pressure.