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# Pump Speed Vs. Torque Characteristic Curve

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## Pump Speed Vs. Torque Characteristic Curve

(OP)
Hi all,

We are dynamically modelling  motor and associated pump in SKM PTW. We ahve obtained the motor characteristic curves with associated inertia.

However, we only managed to obtain the pump inertia and rated torque. We have requested our Mechanical team for the pump speed vs. torque but all they have instead is a pump performance curve that indicates the head and associated flow rates in gallons per minute.

Is it possible to derive the pump speed vs. torque using the pump performance curve? Is the pump speed vs. torque ONLY obtained from the pump manufacturer as an independent curve data?

### RE: Pump Speed Vs. Torque Characteristic Curve

T = 5270 * BHP/N

Where:

T = torque
BHP = brake horse power
N = speed (RPM)

Being

BHP = Q *TDH*SG/(3960*efficiency)

Where:

Q = flow (gpm)
TDH = total dynamic head (feet)
SG = pumped fluid specific gravity

Take also a look at the link below

http://centrifugal-pump.org/speed_torque_curve.html

### RE: Pump Speed Vs. Torque Characteristic Curve

A good question would be 'what type of pump is this?'  One could assume a centrifugal, but that's not necessarily the case.

### RE: Pump Speed Vs. Torque Characteristic Curve

http://www.engineeringtoolbox.com/pumps-speed-torque-d_1114.html

or Google "pump speed torque curve"

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

### RE: Pump Speed Vs. Torque Characteristic Curve

(OP)
First of all, thank you for all your replies.

The starting time is computed as a function of several factors: a) motor and pump inertia, b) motor and pump torque vs. speed, c) motor terminal voltage at different currents (during motor acceleration with pump connected)and d) system impendance/voltage drops during acceleration. Some programs like ETAP would perhaps have an built-in typical centrifugal pump torque vs. speed curve and do curve fitting using the pump rated torque and inertia.

Therefore, deriving the speed vs. torque curve is essential.

### RE: Pump Speed Vs. Torque Characteristic Curve

"Therefore, deriving the speed vs. torque curve is essential."

What is your question?

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

### RE: Pump Speed Vs. Torque Characteristic Curve

(OP)
My question was how to derive a speed vs torque curve from a pump performance curve which was already answered and my thanks for the assistance.

Artisi, the formula for torque in the link you have sent, what is the value of "K"? Are there industry values of K depending on the type of pump? OR is the constant K be obtained from the pump manufacturer to come up with a calculated (estimated) torque vs speed curve?

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