Why are slurry pumps with a large net positive suction head used for liquefied petroleum gas unloading?
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Sliding vane pumps are commonly used for unloading liquefied petroleum gas. These pumps have a high NPSH, usually above 2.5. Given that the height difference between the liquefied petroleum gas tankers and the pumps is quite small, how is unloading still possible? By the way, I would like to ask: 2.5 meters is the net positive suction head for water. When calculating the net positive suction head for liquefied petroleum gas, does one need to multiply this value by 2 (assuming the density of liquefied gas is 0.5, which is half that of water)? Assuming no friction losses, must the liquid level at the inlet of the sliding vane pump be 2.5*2=5 meters? ； 2.5 meters are still enough.
The sliding vane pump is a positive displacement pump, and the pressure at its inlet is already low. Positive displacement pumps have self-priming capability, which is usually evaluated by the suction vacuum height. This vacuum head = 10-NPSHr. The greater the NPSHr, the worse the self-priming ability of the positive displacement pump. For positive-displacement pumps with strong self-priming capability, unloading liquefied gas is no problem. Cavitation problems are more likely to occur when using a centrifugal pump to discharge liquefied gas.
Is the medium in gaseous or liquid state as it passes through the pump?
Can a sliding vane pump be used for loading and unloading liquid ammonia? The manufacturer can offer better performance.
Does that mean a split-case pump can operate normally even when cavitation occurs at the inlet (i.e., when the pressure is below the saturated vapor pressure at that temperature)?
Vacuum head = 10 – NPSHr. This vacuum head applies to water pumps, right? The saturated vapor pressure of water is very low, whereas that of liquefied gas is quite high
The sliding vane pump is equipped with a safety valve, which addresses the issue of transporting gas and liquid together and is suitable for applications requiring a low net positive suction head
Sliding vane pumps can be used to discharge liquid ammonia; you can send me a message for details
I would like to ask: if the sliding vane pump already has a safety valve, is it still necessary to install another safety valve at the pump’s inlet and outlet during design?