Automatic Duty change operation of Pumps

Hi Experts,

I have confusion on the automatic duty change operation of pumps when they are controlled by a PLC in auto mode.

I have seen in control panels that there are 2 modes auto and manual.Manual is the regular start and stop function controlling the pumps.I have confusion on how pumps operate in auto mode controlled by PLC?



Hearing for your valuable response.

Thanks,
Akash

it depends on what the demands were. in my case one pumps starts, then if level still rising second one starts. when the job is done stops. next time first starts pump with less runtime if both are OK (ready and in auto mode).

Or u can have duty changeover after a specific period of time .. say 24 hrs or a week

Hi All,

Thank you for the quick response.It shall be of great help and useful if you could provide PLC programming logic for the Automatic Duty change operation of Pumps.

Thanks,
Akash

I don't like alternating master pumps like that. If you do so, what will probably happen is both pumps will wear out and fail at the same time or in close proximity to each other. Ideally you should have a dedicated master pump that stays the master pump until it needs to be replaced. THEN you switch over to the other pump, which will have much fewer hours on it. You keep that pump as the master until IT breaks down, and keep going like that. Unless there's some advantage to having pumps with an equal amount of wear, I don't see why anyone would do that.

Akash,

If you are sure that you need to do this Pump alternating, then before anyone can help you, you will have to list the brand and model of your PLC, and which version of the programming software that you are using.

There are hundreds of different models of PLCs, and many versions of software. One program that I might write for you may not work for your PLC.

Another tip is that for your specific PLC software, you will need to use a timer or timers that can time for how long each pump should run before switching. Then you will need to set up some alternator logic (also often called "flip-flop" or "toggle" logic).

Hi All,

I'm preferring to do the sample program on S7 1200, TIA Professional, SP2.

The Control philosophy comprises of 3 pumps ( 2 Duty and 1 stand by ). Pump operation needs to be controlled by the PLC ( in auto mode ) with the following function, apart from the regular manual mode of start and stop of pumps in the control panel.

- Constant pressure control through continuously variable adjustment of the speed of the pump.

- PID Controller with the adjustable PI parameters.
-Constant pressure at set point, independent of inlet pressure.

Please note, pumps need to be started based on the pressure in the network.Under normal operation, the system will remain pressurized. All pumps need to be stopped when set point (P1) is reached.When pressure falls below P1, the pump which is assigned as Duty should start automatically on VFD and should run until P1 is maintained.If it could not able to do this, Assist Pump should start automatically until P1 is maintained.If any of the Duty pumps fails, stand by should come in to action.

Also, pumps need to change there Duty in next cycle automatically ( Assist pump should come as Duty pump and Duty pump should come as Assist pump for the next cycle ).

Does Counters find solution for the Duty change automatic cycling operation of pumps?
Kindly help me up in sharing the programming logic.

Hearing for the valuable response.

Thanks,
Akash

brstilson said:

I don't like alternating master pumps like that. If you do so, what will probably happen is both pumps will wear out and fail at the same time or in close proximity to each other.

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I don't see a problem here. If motors (pumps) are important on some particular site one should hold to maintenance service schedule, and that is usually x runtime hours or yearly. so if you service pumps yearly i do not believe that they would fail in approx. same time. usually service will tell you if it is time to replace it. it is also not good for motor to stand by for long time. also, pumps do not have to necessarily change at same time, you can set the changeover after each 100 or 200 hours

akashu said:

Does Counters find solution for the Duty change automatic cycling operation of pumps?
Kindly help me up in sharing the programming logic.
Akash

Click to expand...

i'd go with runtime hours compare. if 1 < 2 then latch bit for P1_next, else unlatch it.
If P1_next then first start P1 else P2
If one is in error then

• if only one needs to run do nothing (just signal error)
• If both needs to run then start spare P3

So you'll have duty change over between P1 and P2, and spare will start only when P1 or P2 are out and both needs to run (or, which is unlikely, if both fail)

PS: i think there's a typo. you need to have two pressure points, one setpoint and one treshold.

brstilson said:

I don't like alternating master pumps like that. If you do so, what will probably happen is both pumps will wear out and fail at the same time or in close proximity to each other. Ideally you should have a dedicated master pump that stays the master pump until it needs to be replaced. THEN you switch over to the other pump, which will have much fewer hours on it. You keep that pump as the master until IT breaks down, and keep going like that. Unless there's some advantage to having pumps with an equal amount of wear, I don't see why anyone would do that.

Click to expand...

I've seen it done this way to ensure that both pumps are exercised. For instance if one pump runs all the time for three years, then fails and the other is seized solid as its not been run then you immediately have a complete loss of production while both pumps are repaired. If you cycle them it's true that they will have a similar amount of wear but they probably wont both fail at exactly the same time and when one fails you replace it and purchase the parts to replace the other the next time they changeover.

Edit: you could cycle them based on different intervals Pump 1 swaps every 5 days, pump 2 swaps every 4, giving them both exercise but ensuring that one pump always has more wear on it than the other.

Everyone's got their own take I guess, it also depends on preventative maintenance and the particular application.

Balash, I should have read your later posts as you've already suggested variable changeover rates, Apologies!

Cheers,

Lee

Also, pumps need to change there Duty in next cycle automatically ( Assist pump should come as Duty pump and Duty pump should come as Assist pump for the next cycle ).

Does Counters find solution for the Duty change automatic cycling operation of pumps?

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Counters are not normally used for the alternator function. There have been many versions of the alternator logic for ALlen Bradley RSLogix PLCs posted on this site. Do an Advanced Search on this site for keyword "Siemens alternator". You should find about 3 posts but only one seems to have a solution method.

http://www.plctalk.net/qanda/search.php?searchid=3170133

Thanks Lancie1.

Akash

Give me an email address and I will send you a function block for a pump alternator if you dont already have it.

Since nobody has posted to the thread in the last three years, I think its safe to assume the OP has either solved the problem or moved on to bigger and better things.

brstilson said:

I don't like alternating master pumps like that. If you do so, what will probably happen is both pumps will wear out and fail at the same time or in close proximity to each other. Ideally you should have a dedicated master pump that stays the master pump until it needs to be replaced. THEN you switch over to the other pump, which will have much fewer hours on it. You keep that pump as the master until IT breaks down, and keep going like that. Unless there's some advantage to having pumps with an equal amount of wear, I don't see why anyone would do that.

Click to expand...

In my experience the likelihood of both pumps wearing out a exactly the same number of operating hours is much lower than the certainty that a pump that sits idle for long periods of time will fail shortly after starting because the bearings and stuffing box have deteriorated from sitting there.