×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Pump Speed Vs. Torque Characteristic Curve

Pump Speed Vs. Torque Characteristic Curve

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

You can calculate the required power BHP=(GPM*H*Sp.Gr.)/3960/eff for any rpm
and from T=5252*HP/RPM calculate the torque or :
The torque=Trated*rpm^2/rpmrated^2 at any rpm.
 

RE: Pump Speed Vs. Torque Characteristic Curve

One can get the flow, head, and power for 7anoter4's equation from the centrifugal pump affinity laws:  gpm2/gpm1=rpm2/rpm1, h2/h2=(rpm2/rpm1)^2, BHP2/BHP1=(rpm2/rpm1)^3.  Assuming you're talking about a centrifugal pump.

RE: Pump Speed Vs. Torque Characteristic Curve

Pump torque is a function of many factors other than speed alone.

RE: Pump Speed Vs. Torque Characteristic Curve

The mechanical engineers should be able to provide a system resistance diagram (which can then be related to pump shaft speed, though pump affinity laws).

I assume you are starting DOL and hence can obtain a Torque / Speed curve for the motor.
You either know or can find a relationship between motor and pump speed.
Knowing" alpha = T (motor torque available - pump resistive torque) / I (motor + pump etc inertia) and

and alpha = dw (change in shaft speed) / dt (time step)

You can assume a dw (say 100 th of the final shaft speed - though you need to try refining to ensure you have selected a suitable dw) and step along the "dw's" until the final shaft speed, whilst calculating "dt" along the way. The sum of "dt's" is your starting time.

I have previously evaluated the starting time by computational methods (stepping in Excel). Definite solutions exist (cf computational methods), though for what you are doing it may be easier and accurate enough to do via computational methods.

Regards,
Lyle
 

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.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources