I thought that rated flow & rated pressure of a centrifugal pump is at BEP. But
as I am looking at some pump manufactures curves, I see that the rated flow &
pressure point is at left side of BEP. If a fire pump is suggested to work at
it's rated capacity, so why it is not at BEP?
Look at the pump curve with marked BEF and rated capacity here at
http://www.esmaeili.org/Pump.jpg
I have seen some definitions for rated capacity, rated pressure and rated
speed in FM approval standard for as below:
Rated Capacity: Capacity at rated pressure and rated speed.
Rated Pressure: Pressure developed by the pump when operating at rated
capacity and rated speed.
Rated Speed: The speed for which the fire pump is listed and appears on the
fire pump nameplate.
I know that a fire pump shall furnish not less than 150 percent of rated
capacity at not less than 65 percent of total rated head & the shutoff head is
limited to 140 percent of the rated head.
All the above definition are related to each others, i would like to know how
rated capacity & pressure of a centrifugal pump are determined by listing
companies like UL. I am not looking for a very technical answer, I just want to
know it simply.
For example, for the curve you can see at http://www.esmaeili.org/Pump.jpg
The speed for which the fire pump is listed is 1470Rpm so rated speed is
1470Rpm, so let's say UL to determine the pump curve will run the pump at
1470Rpm at suction lift of 15 ft at various flow rates to generate total head,
power, and efficiency curves. The best efficiency point in curve is BEP but how
can UL determine the rated capacity and pressure of the pump?
Imagin that you have a chinese pump, you have only a pump curve sheet, the
pump is not listed, and there is nothing about rated capacity of the pump
written on the pump plate, as per NFPA 20 the pump shall furnish not less than
150 percent of rated capacity at not less than 65 percent of total rated head,
but you don't know where is rated capacity to check if the pump can satisfy
NFPA 20 requirements, then what will you do to determine rated capacity?
NOTE: I know that using non listed fire pumps are not allowed by NFPA, this
is only a scenario for determination of rated capacity.
Thanks for your attention in advance.
Reza
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