LPG centrifugal pump
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Our liquefied gas centrifugal pump has to start and stop frequently due to insufficient throughput, and the inlet pressure does not reach the designed level. The seals get damaged frequently; could it be that insufficient inlet pressure leads to cavitation? Does anyone know the formula for calculating the net positive suction head? ? ? {:3_65:}
NPSHa = Pc/rg + Hg – Hc – Pv/rg, where Pc is the pressure at the liquid surface, and Hg represents the backflow height; a negative value is assigned if suction is involved. Hc represents the pipeline loss; Pv is the vaporization pressure of the medium, r is the density of the medium, and g is the acceleration due to gravity (9.81). All values are calculated using absolute pressure. The frictional loss in the piping along a typical inlet is around 2 meters per 100 meters; adding the local losses from valves and filters gives the total loss
Cavitation is caused by insufficient outlet pressure. Increase the diameter of the pump’s inlet pipe, or reduce the size of the outlet valve
If a single-face mechanical seal is used, it is recommended to switch to a tandem seal
Pumps with low inlet pressure are prone to cavitation, and their mechanical seals tend to fail easily.
This post was last edited by backcat666 on 2018-7-31 at 15:41. The cartridge pump uses a tandem double mechanical seal without pressure, i.e., a face-to-back arrangement; the flushing scheme is P52+P11+P13, and it performs very well
Previously, for liquefied gas propylene as well, we used bag pumps with pressure-free mechanical seals; the newer pumps now are bag pumps equipped with pressure-type mechanical seals and a 53B flushing system. We still don’t know how they will perform in practice, as we lack experience with using the 53B system
If the nitrogen storage bag is not in use, it’s P52:lol