2 replies to this topic

[betty]

Hi all,

I want to ask about balancing drum, a device to compensate high axial thrust in multistage pump. Only multiple impeller pump will use such balance pump? How does it affect the pump?

thank you very much..

[breizh]

Hi Betty,

Will it help?

http://d-tech_hu.web...ochures/WDX.pdf

Breizh

[pavanayi]

Betty,
Normally, balancing is used in centrifugal pumps/compressors which have a big enough difference in suction and discharge pressures (usually multistage devices) and which will hence have a comparitively high axial thrust (on a HP--> LP direction). This reduces the load on the thrust bearing on the LP side of the machine. Continuous loading of this thrust bearing for long periods will lead to failure of the bearing.
Also, it is important to note that when a balancing drum/disc is used, there will be leakage from the HP side into the balance drum, which will be recycled to an appropriate location within the pump/compressor. When due to wear the leakage rate increase, the amount of fluid recycled within the pump/compressor increases thereby reducing the efficiency of the machine.

Another way of reducing the axial thrust in some multistage centrifugal pumps are when the stages (impellers) are configured on the pump shaft in such a way that the discharge stage is somewhere in the middle of the pump (not at one end). I have seen BFW pumps which had suction pressure at 1.5 barg and discharge pressures at 150 bar g use this method to reduce the thrust.

The type of thrust reduction to use (to arrange impellers or to use balancing) is dependent on the geometry of the pump. Axially split pumps favour the impeller arrangement whereas barrel pumps usually have the balance drum.

I hope this has answered your query. Please note, this is a chemical engineer's understanding of the pump/compressor internals. Please refer to a mechanical engineer/pump manufacturer for better understanding of the whole concept.