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Pump Destaging


In many applications the required differential head of a pump may decrease
because of a change in specific gravity, or in system pressure requirement. In
such event, its head can be reduced by reducing its speed, if the pump is driven
by a variable speed driver such as VFD, engine, or turbine.

If a pump is connected to a constant-speed motor, its head can be reduced by
trimming the impeller diameter or, in multistage pump, by de-staging the pump.

Destaging is the removal of one, or more, impellers to reduce the head developed
by a multistage pump. In many situations, destaging is preferable to trimming the
impellers. Examples of these situations are: [ * ]

If done properly, destaging will have no, or minimal effect on pump efficiency.
The proper procedures for destaging a multistage pump are: [ * ]

In this example of a destaged horizontal pump there are ways the destaging can
be improved. These are: [ * ]


[ * ] Some information are excluded on this article.
Read more.


R: 0110-PUDE
C: operation, hydraulic re-rate
F: destaging
Questions


I have an application for a 6-stage vertical pump with 12" diameter bolted bowls.
My client wants to destage the pump to 4 stages but, for operational reasons,
wants to remove the two impellers only and retain all of the 6 bowls. Does anyone
have a formula for calculating the head loss through the two "empty" 12" bowls?


Why do we need to re-size the throttle bushing when destaging only one impeller
in a 10-stage pump, and what are the calculation basis for the new bushing size?
It seems to us that the pump thrust bearing should be able to handle a 1/10th
reduction in pressure.


I work in a power generation plant. Due to fluctuating demand we find ourselves
changing rotors with different stage configuration on some of our pumps. I noticed
that, depending on the manufacturer, some rotors are balanced by changing
either the balance pieces at the center, or by changing the throttle bushing and
sleeve at  the high pressure stuffing box. The different balancing methods are
creating confusion among our shop personnel. What are the reasons for this
difference, and should Hi or API come up with a unified balancing method in their
standards?


Comments?
Related topic

Magnitude and direction of axial thrust in destaged pump
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