Why can't the inlet of centrifugal pump be negative pressure?
Therefore, the centrifugal pump inlet pressure can be negative, and negative number, should be used to pump cavitation margin and liquid saturated steam pressure parameters to specific calculation. Sometimes, the liquid saturated steam conveying pressure is very high, such as the 9 m water column, then the minimum pressure of the pump inlet should be equal to 4+9=13 meters, the atmospheric pressure is higher than 3 meters, not only for negative pressure, even higher than the atmospheric pressure to work properly.
Can be negative pressure ah, the negative pressure here refers to the pressure is less than the atmospheric pressure, but the pressure can not be too low, to prevent water vapor below the saturated vapor pressure, so that water vaporization, cavitation phenomenon, the centrifugal pump will be considered.
However, the centrifugal pump will have its import pressure requirements, which is to prevent cavitation, that is, the fear of the delivery of liquid at low pressure will occur gasification. Centrifugal pump has an important parameter called NPSH, for example relating to the inlet pressure, the pump NPSH, 4 meters, it means that the absolute pressure of imports should be higher than the saturated steam conveying fluid pressure of liquid column is 4 meters high, so, when it is at a temperature of saturated vapor pressure for water transport 2 meters, 4+2=6 meters minimum inlet absolute pressure. Because the absolute pressure is 10 meters water column atmospheric pressure, at this time the entrance negative pressure is 10-6 meters =4 meters water column.
The entrance can be a negative pressure. You can often see someone pumping water from the pool. How can you pump water if it is not negative pressure?
