Pumps with VFDs 3

[sdbarry]

Dear Fellow Members

This is Sulaiman Dawood working as a Project Engineer in Energy Futures Consulting.

I am doing a project for a client and I am stuck at pump analysis with VFDs.

The nameplate of a pump is attached along with the pump curve.

Can you please guide which curve to use with the nameplate's parameters? Also, how will the pump input power change if we reduce the rpm, given that BHP is 18.8kW on the nameplate?

Looking forward to your guidance.

Best Regards

Sulaiman

 

[LittleInch]

Do you really know virtually nothing about pumps?

First get the KSB chart for nominal 3000 or 2950 rpm.

Then to find the impeller diameter of pump find out where on the 3000 rpm chart, a duty point of 500 US GPM and 125 ft head sits. That becomes your curve which is in parallel with the min and max diam curves.

Then for a VFD the performence of any point on the curve changes more or less in proportion to the affinity laws.

Flow is proportional to the relative speed compared to 3000 rpm. So say 3750 rpm or 25% more than 3000 will give you 25% more flow. 2250 rpm 25% less
Head is proportional to rel speed ^2. So 25% more speed is 56% more head, equally 25% less is 56% less head
Power is proportional to rel speed ^3. I think you get the drift now??

But you can't exceed the power of the motor without it going up in smoke.

Does that make sense?

 

[bimr]

Based on your limited knowledge of pumps, you will be well advised to contact the local pump supplier and review the application with him.

 

[Snickster]

That is not the curves for the 2900 RPM pump speed as indicated on the nametag. That curve is for a 3500 RPM pump speed as indicated on the curves at the top. You need to first locate 2900 RPM pump curves. I looked on KSB website link below and could not find the RPK model. Perhaps it is an obsolete model. Where did you get those pump curves?

KSB product catalogue for efficient pumps & valves

KSB offers highly efficient pumps and industrial valve solutions including all technical data. Find the best KSB solution for your application and needs here.

www.ksb.com

Once you find the correct pump curves you can proceed as Little Inch described unless you can find the actual reduced RPM curves then you don't have to manually use the affinity laws.

 

[GD2]

IMHO, best you call the KSB vendor to give you a presentation and take a training with a Third Party training provider. From your question, I feel, you will mess up this project if you are a novice and without a knowledgeable Supervisor.
There is too much to learn and know about pump before you take responsibility and accountability.

 

[georgeverghese]

Agreed the speed on the titlehead on the pump curves does not match the nameplate speed.
Agreed, the symbology used on the pump curves is not clear.
What you need is pump curves for a given pump (RPK 80-200) at various speeds, while the pump curve you've posted is for various impeller configurations at a fixed speed of 3500rpm. Perhaps the reason for reaching out to E-Tips is because you're not getting much out of KSB at the moment.

 

[sdbarry]

That is not the curves for the 2900 RPM pump speed as indicated on the nametag. That curve is for a 3500 RPM pump speed as indicated on the curves at the top. You need to first locate 2900 RPM pump curves. I looked on KSB website link below and could not find the RPK model. Perhaps it is an obsolete model. Where did you get those pump curves?

KSB product catalogue for efficient pumps & valves

KSB offers highly efficient pumps and industrial valve solutions including all technical data. Find the best KSB solution for your application and needs here.

www.ksb.com

Once you find the correct pump curves you can proceed as Little Inch described unless you can find the actual reduced RPM curves then you don't have to manually use the affinity laws.

Thanks @Snickster , you identified correctly. The motors installed have a year of manufacture of 1993.

I am waiting for OEM support. Meanwhile, I've identified 200 mm impeller matches our requirement.

 

[sdbarry]

IMHO, best you call the KSB vendor to give you a presentation and take a training with a Third Party training provider. From your question, I feel, you will mess up this project if you are a novice and without a knowledgeable Supervisor.
There is too much to learn and know about pump before you take responsibility and accountability.

Thanks. You are right. I'll have asked the KSB support team.

Meanwhile, my supervisor will also go through my calculation as well.

 

[sdbarry]

Agreed the speed on the titlehead on the pump curves does not match the nameplate speed.
Agreed, the symbology used on the pump curves is not clear.
What you need is pump curves for a given pump (RPK 80-200) at various speeds, while the pump curve you've posted is for various impeller configurations at a fixed speed of 3500rpm. Perhaps the reason for reaching out to E-Tips is because you're not getting much out of KSB at the moment.

Yes @georgeverghese , I've asked ksb support team as well. I am short on time, which gave me an idea to consult experienced persons.