Page 87 - Know and Understand Centrifugal Pumps

Know and Understand Centrifugal Pumps

is 348 gpm. The process engineer should instruct the operators to
always maintain the flow above 350 gpm unless he's prepared for pump
failure and stalled production.
In the third example, the line terminates at 53%. This means DO NOT
run this pump at less than 53% of the BEP. 53% of 4500 gpm is 2385
gpm. Because this is a firewater pump and because firemen need to
throttle the nozzles on their fire hoses, then we need to install a
pressure relief valve on this system with a discharge bypass line so that
the pump dumps the restricted water (less than 2400 gpm) back into
the suction tank or lake. If not, this firewater pump is likely to suffer
bearing failure during an emergency.
The operating window is the effective zone around the REP on the
pump curve that must be respected by the process engineer and/or the
operators of the pump. How far away from the BEP a pump can
operate on its performance curve without damage is determined by its
impellers suction specific speed.

Open impellers
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Impellers are also classified as to whether they are:

1. Totally open,
2. Semi-open (also called Semi-enclosed), and
3. Totally enclosed.
Most totally open impellers are found on axial flow pumps.
This type of impeller would be used in a somewhat conventional
appearing pump to perform a chopping, grinding, or macerating action

Figure 6-16
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