Pump Speed Adjustment - Ramping

JohnDG, states it pretty good.

Its great to have a starting point, but depending on your system, you start with your starting point and you make adjustments from there.

And of course having the same pump size for both pumps is a requirement.... (even though I have seen different pump sizes in parallel), With the same pump size and impallar size, this improves efficiency to keep the pumps from fighting each other.

One thing that you obviously want to avoid is and surges that would cause water hammer.

As my dad would say, "The fifty-cent answer". Well done by the way. I would have nothing more to add.

.

My wife wouldn't be near as polite.

You wouldn't happen to have any links or directions to who's designing / manufacturing such intelligent real time systems ?

1. Maintaining "set point" value in any process is critical to the process outcome.

Set point(s) in any process must be optimized for maintaining safe, stable, reliable control of the process.

In this case dangerous over-pressurization of the piping system could be caused by allowing both pumps to operate at their maximum output level rather than make them maintain a process set point value.

I am sure the designer (engineer) based the pump criteria on system limitations and process demand therefore any major deviation from design specifications could result in unwanted control issues and possibly equipment failure.

It is not a ever good idea to operate any equipment outside design specifications.

If the design does not meet process requirements, the system requirements must be re-evaluated and all aspects taken into consideration, then all of the system equipment updated or modified to safely accommodate the change in operation.

2. If the pumps are not operating at the same speed, there will be surging created in the system pressure and flow which can/will be detrimental and/or hazardous to the pumps, pump motors, and the piping system components.

3. The method used for ramping of the motor speed is determined by the type of speed control used and/or the programming method selected.

4. Depending on drive type and design; stepped motor speed changes can be limited and controlled by drive design parameters or may be left up to the drive programmer.

The factory Installation and Operation Manual on the drive(s) should contain answers to these and other questions.

Thanks everyone for great and detailed answers, it really means a lot!

For the Set points, how would those be selected, based on calculation only, or maybe by testing during the commissioning stages?

IMHO, they should be a calculated value that is confirmed during commissioning, and adjusted as needed to operate as specified prior to final signoff. To what extent that is can vary based on complexity of the overall design and the knowledge base of the designers, but ultimately shouldn't matter too much to you as client should it?

Calculating guessing the set points is fine, but, pump curves and performance figures from the pump manufacturer will never match the performance you get from a pump after it is plumbed into the system and started and run.

A1) Because if it didn't, then either too little or too much water would be flowing. The reason for changing the speed of the pump is a change in the pressure/flow characteristic of the system into which the flow is being fed; no change in pump speed would mean too little or too much water being delivered.

A2) Because if they weren't, assuming the pumps are identical, then the faster pump would pump virtually all the water and the slower pump would pump virtually none so there would be no point in running the second pump.

A3) Because if it were step-wise then it wouldn't be a speed ramp. The ramp is there to obviate the risk of water hammer in the valves and pipework.

A4) See A3 above.

<...waiting for the review of pump specialist...> It might be a long wait, because this stuff is actually Control Engineering and Process Engineering.