Flow rate change in centrifugal pump without changing impeller size or motor power or motor speed 5

[Nick47]

Hello,
There is centrifugal pump with constant speed (no VFD), as per pump curve it can provide different flow rate which will cause to have different DH.
How would it be possible to have higher/ lower flow rate from the pump without changing the impeller size, motor speed, and no change in suction and discharge line?
Thanks for your advise.

 

[1503-44]

Every system can be different, but there are commonalities in typical well-designed systems, and those do not deviate widely from my 30% flow away from BEP rule of thumb. If you are almost always between 80-100% BEP, control valves will do the job better and always at less cost. If you spend 40% or more of the pumping time at < 75% BEP flow and reduced head output works for the system curve, vfd are typically better for single unit systems.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[Valvecrazy]

I agree. At flow rates well below BEP a VFD maybe wasting a little less energy than a control valve. But a VFD is not "saving energy" as varying the speed will cause more energy used per gallon pumped, similar to a control valve.

 

[pierreick]

Hi,
About VFD I encourage you to take some time to read the document attached.
Edit:

https://www.google.com/search?ie=UTF-8&oe=UTF-8&q=Inverter.&btnG=Search&domains=https://

http://www.pumpfundamentals.com&sitesearch=https://www.pumpfundamentals.com

Pierre

 

[Valvecrazy]

Good article. Been around a long time and written with bias.

In conclusion we hope that this guide encourages the use of variable
speed pumping, in appropriate applications, leading to cost savings from
both reduced energy consumption and increased pump system reliability.
John Bower
Manager of Engineering and Technology
Flowserve UK
(Chairman of the VSD Group)

With PD pumps or when the head can be reduced VSD can save energy. But I do not think centrifugal pumps with a high static head should even be mentioned in an article about VSD energy savings.

They need to greatly expand on this quote.

However, in systems dominated by static head, the pump efficiency
changes with the speed. It is typically reduced at lower speeds and hence
energy savings may not always be realised (see Section 4.2.2)

I have not been able to document anything but energy losses with VSD using centrifugal pumps at high static head.

 

[1503-44]

"But I do not think centrifugal pumps with a high static head should even be mentioned in an article about VSD energy savings." Ditto that. Vsd with high head is a loser. As is vsd and constant flow.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[moideen]

Thanks to all the consultants, LI, valvecrazy, and 1504, I enjoy participating in an interesting subject with experts, which is a little complicated to me. As LI stated, VFDs are not always suitable for all systems, especially in static-dominant or constant static-head applications like booster pumping. I totally agree.
LI stated, “This flattens the system curve and also means lower flow heads higher pressure than your assumption of head being directly proportional to flow^2.”
What I depicted on the curve is that, when VFD is used to reduce the flow, the head will be following the affinity law (final speed (1194/1490)2*159=102 ft/hd. Instead of VFD, the system curve moves to the left when regulating the balancing valve, and it points at 172 feet/hd.


The problem with the world is that intelligent people are full of doubts, while stupid ones are full of confidence.
-Charles Bukowski-