Parallel VFD Pumps Speed setpoint 1

[FilipRST]

I have two VFD pumps emptying wet well. It is defined Duty 1 and Duty 2 Start and Stop setpoint and pumps minimum and maximum speed.
If we have just one (Duty 1) pump running speed is easily defined by the slope (MaxSpeed-MinSpeed)/(Duty1StartLevel-Duty1StopLevel).
In case when the level is above Duty2StartLevel we will have two pumps running in parallel (Duty2StopLevel is above Duty1StopLevel as it is Duty2StartLevel above Duty1StartLevel.
What would be the speed of the pumps running in parallel? Thank you for any help and ideas.

 

[LittleInch]

Both need to be the same speed.

Why the vfds though?

What are you controlling on?

Trying to keep a constant flow?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EdStainless]

Do the pumps match?
Will they see the same pressure at the intake?
This is good in order to keep them seeing the same conditions.
When we did this we would slave pump 2 off of drive 1 so that they would run frequency locked.

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P.E. Metallurgy, consulting work welcomed

 

[bimr]

More information is needed, such as pump curves, pump HP, type of pump, system headloss, etc.

 

[goutam_freelance]

Assuming that you intend to keep two pumps running in parallel for some time when level is above duty2StartLevel. The pump speed has to be same otherwise the lower speed pump will not take load. The load will be distributed among the two pumps depending on Q-H curve of each pump. If there is small variation in Q-H curve one pump will pump little more. All the pumps need to have drooping Q-H curve to be able to run in parallel.

Engineers, think what we have done to the environment !

https://www.linkedin.com/in/goutam-das-59743b30/

 

[LittleInch]

My response assumes both pumps are "identical". If they aren't then it would be a different answer.

But we don't really know what you're control point is.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Artisi]

At the moment, the only thing we are sure of is that both pumps will operate at the same discharge head, anything else is crystal ball gazing


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.)

 

[1503-44]

You don't know that yet. The pumps are running in parallel, but it is not stated to where each pump's discharge is connected.

 

[Artisi]

1503-44,well it was an assumption, and if not connected we know even less.

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.)

 

[FilipRST]

The application is related to the collection system and pumps are pumping out to the same discharge point.

 

[georgeverghese]

Careful there, you may be deadheading pump 2 when you first start it at min speed, if the head developed at min speed is less than the superimposed head.

 

[Artisi]

Same discharge point via a common discharge line?

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.)

 

[1503-44]

Artisi, Happy to see your danger in making assumption warning is back.

FilipRST Can you design an electrical supply without knowing the circuit configurations? Pumps are only half of your system. You need to explain how the pipes are connected, diameters, lengths and end of pipe discharge pressures.