Pumps control - advice

plutonium · Jun 21, 2017

Hi forum,

I would like to know the best way to control work of 3 pumps depending on working hours. 2 of 3 pumps should work, while 1 should be stopped but ready to start.

After X hours, pump with most working hours should stop and the one which was stopped, should start.

And cycle repeats again after X time.

Thanks

Saffa · Jun 21, 2017

Wearing out all your pumps equally sounds like a good idea.. but it's not. We prefer a 75/25 ratio so that when one pump is on its last legs, your reserve pump still has some life left in it.

As for the rotation logic... just totalize hours. When a pump becomes duty, it's "rotation Setpoint" becomes current run hours + X hrs. Then when your total hours equals that, you trigger a duty rotation.

That way you can assign X hours to P1 and 2, but X*0.25 to P3 and retain some life in it.

boneless · Jun 21, 2017

I agree with Saffa, however we run for a much shorter time. Generally we would run the standby pump for about an hour every day. This way you are sure your pump is operational, but would be less likely to break at the same time.

You should make sure you can start/stop the pump on the fly as well, some applications do not like that. You would be better off changing duty status when the pumps is stopped by the process.

metwally.mustafa · Jun 21, 2017

Saffa said:
Wearing out all your pumps equally sounds like a good idea.. but it's not. We prefer a 75/25 ratio so that when one pump is on its last legs, your reserve pump still has some life left in it.

As for the rotation logic... just totalize hours. When a pump becomes duty, it's "rotation Setpoint" becomes current run hours + X hrs. Then when your total hours equals that, you trigger a duty rotation.

That way you can assign X hours to P1 and 2, but X*0.25 to P3 and retain some life in it.

can you describe in details these type of operation please . it will be helpfull if there is a PDF file or a paper

PLCnovice61 · Jun 21, 2017

plutonium, please excuse my cynicism(which seems to be endless),
what you really mean, without PLC details, please supply code how to do it and hurry UP(l know you didn't say ASAP).
Of course he could have searched the never used before "flip flop".
Funny how later it it is the more cynical l become, maybe l meant how later l drink re above!

Saffa · Jun 21, 2017

I read this forum on my phone, so do not normally have easy access to code.

Let's take another approach which results in less liver damage for PLCnovice61.

How about you show us what you've tried, and tell us what isn't working, then we'll give you some suggestions.

daba · Jun 21, 2017

Why does everyone want to balance pump run hours ...

I've done several posts on this subject... my post title says it all...

Totally agree with Saffa, and boneless for checking that a pump designated as a "standby" will actually run if needed...

Whatever algorithm you come up with should minimise multiple concurrent pump failures, or maintenance schedules.

OkiePC · Jun 21, 2017

Unless it is a brand new installation (all new pumps), balancing run hours is just fine. Often in the water industry it is important that all pumps run so that no liquid stagnates in any lines. Using run hours is a simple way to figure out "who's next lead", but most of the time, I use a rotation that just cycles through all the available pumps. I keep track of run hours for each pump, but only once was I asked to use least run hours as the basis for "lead pump".

As stated, there are always more conditions to determine the run order but with three pumps or less it is usually not too hard to write the logic to make sure the pump you want to lead with is ready. Most of the systems I work on have physical "HOA" selector switches, SCADA and/or Local HMI mode controls as well as "VFD ready" inputs and "fail to start" alarms that can take a pump out of the sequence if for any reason it does not start within a few seconds after being called. All of those considerations need to go into the logic.

plutonium · Jun 23, 2017

Saffa said:
Wearing out all your pumps equally sounds like a good idea.. but it's not. We prefer a 75/25 ratio so that when one pump is on its last legs, your reserve pump still has some life left in it.

As for the rotation logic... just totalize hours. When a pump becomes duty, it's "rotation Setpoint" becomes current run hours + X hrs. Then when your total hours equals that, you trigger a duty rotation.

That way you can assign X hours to P1 and 2, but X*0.25 to P3 and retain some life in it.

Thanks for info.

So basically good idea is to use first 2 pumps + once a day for half an hour to use third just to see if it is alive and to prevent stalling or other faults due inaction.

PLCnovice61 said:
plutonium, please excuse my cynicism(which seems to be endless),
what you really mean, without PLC details, please supply code how to do it and hurry UP(l know you didn't say ASAP).
Of course he could have searched the never used before "flip flop".
Funny how later it it is the more cynical l become, maybe l meant how later l drink re above!

Luckily you are wrong.

daba said:
I've done several posts on this subject... my post title says it all...

Totally agree with Saffa, and boneless for checking that a pump designated as a "standby" will actually run if needed...

Whatever algorithm you come up with should minimise multiple concurrent pump failures, or maintenance schedules.

Unfortunatelly investor is who wants that to work in that way. I will try to talk to him and change his mind.

OkiePC said:
Unless it is a brand new installation (all new pumps), balancing run hours is just fine. Often in the water industry it is important that all pumps run so that no liquid stagnates in any lines. Using run hours is a simple way to figure out "who's next lead", but most of the time, I use a rotation that just cycles through all the available pumps. I keep track of run hours for each pump, but only once was I asked to use least run hours as the basis for "lead pump".

As stated, there are always more conditions to determine the run order but with three pumps or less it is usually not too hard to write the logic to make sure the pump you want to lead with is ready. Most of the systems I work on have physical "HOA" selector switches, SCADA and/or Local HMI mode controls as well as "VFD ready" inputs and "fail to start" alarms that can take a pump out of the sequence if for any reason it does not start within a few seconds after being called. All of those considerations need to go into the logic.

Installation is brand new and is used for pools water circulation through filters. Pumps will have soft starters to prevent pressure kick during start up.

GTUnit · Jun 23, 2017

Search or Google "Pump Sequencer logic" for a bunch of examples.
Many VFDs listed as having "pump" features have built in sequencer and lead lag configurations were they talk to each other and handle the switch overs. Very cool.

Saffa · Jun 23, 2017

GTUnit said:
Search or Google "Pump Sequencer logic" for a bunch of examples.
Many VFDs listed as having "pump" features have built in sequencer and lead lag configurations were they talk to each other and handle the switch overs. Very cool.

I have never had much luck with these. I have received a few jobs to go and "fix" these set ups which were specced by consultants. They work ok until something goes wrong... Had one sewage lift station overflow into the harbour because the controller inside cards decided that a pump had done too many starts so it took it out the sequence. So the next pump started doing too many starts so its controller did the same until all 3 pumps were unavailable.

Had another almost do the same when one drive lost its level signal. So it sat there as the duty pump, telling the standby one "don't run, I'm duty and the level is low".

I realize PLCs or RTUs can also be programmed with dumb things, but when you have a good "standard" program, it's nearly impossible for anyone to inadvertently break things by incorrectly configuring a drive. Even my most technologically challenged sparky can connect the 10 control wires required for my standard drive interface, and change the 6 odd parameters required.

GTUnit · Aug 10, 2017

Saffa said:
I have never had much luck with these. I have received a few jobs to go and "fix" these set ups which were specced by consultants. They work ok until something goes wrong... Had one sewage lift station overflow into the harbour because the controller inside cards decided that a pump had done too many starts so it took it out the sequence. So the next pump started doing too many starts so its controller did the same until all 3 pumps were unavailable.

Had another almost do the same when one drive lost its level signal. So it sat there as the duty pump, telling the standby one "don't run, I'm duty and the level is low".

I realize PLCs or RTUs can also be programmed with dumb things, but when you have a good "standard" program, it's nearly impossible for anyone to inadvertently break things by incorrectly configuring a drive. Even my most technologically challenged sparky can connect the 10 control wires required for my standard drive interface, and change the 6 odd parameters required.

You make some very valid points and I will definitely keep them in mind.

Pumps control - advice

plutonium

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Saffa

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boneless

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metwally.mustafa

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PLCnovice61

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Saffa

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daba

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OkiePC

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plutonium

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GTUnit

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Saffa

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GTUnit

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