16 pumps in parrallel (Pressure control)

plcsoftvsd

Member
Join Date
Sep 2007
Location
23 15 13.2 N 77 27 28.75 e
Posts
132
Hi,

The project is as under...

a)16 centrifugal pumps of which 4 pumps have Variable speed drives and will pump water into a common discharge manifold.

b)The objective is to keep constant water pressure 4.1 bar.

c)The VSd driven pumps to start first and when the demand is not met by these 4 pumps then the other pumps(with no VSD) will kick in till the pressure is achieved.

d)I have started writing a program using a Twido PLC with one analog input ( 4-20ma) from a Pressure transmitter (Discharge pressure) and one PID controlled analog output 0-10 vdc which will be parralled to all the four drives.

e) When all four VSD's are ON and still the analog output value is higher than 5 VDc then the other pumps will kick in.

f)Now the tricky part is to keep all the pumps to have same running hours.

I have attached a draft twido program ..appreciate any ideas/corrections.

Cheers.
 
Last edited:
Your solution is easy. Buy four drives with pump/fan/rotation software in them. ABB is one of those brands but there are likely others.

Let each drive run one pump variable speed and add or subtract three more across the line as needed. No need to write anything accept, I suppose, a check.

Do a search for PFC Macro and you will see exactly what you are asking for.
 
Your solution is easy. Buy four drives with pump/fan/rotation software in them. ABB is one of those brands but there are likely others.

Let each drive run one pump variable speed and add or subtract three more across the line as needed. No need to write anything accept, I suppose, a check.

Do a search for PFC Macro and you will see exactly what you are asking for.


Oops,..i have to tell..at present the 4 quadraplex skids are already working but they tend to fight each other since the 4 VSDs are trying to achieve the same pressure.

That is the reason i thought of using 1 PLC and give the output from PLC to all VSD's ( they are Altivars from Schneider).

cheers.
 
I am not a pumping expert, but I was always sure that pumps are being cascaded for higher pressure and paralleled for higher productivity.
That is, the productivity may be maintained constant in the mentioned application, not the pressure.
Am I wrong?
 
Last edited:
I am not a pumping expert, but I was always sure that pumps are being be cascaded for higher pressure and paralleled for higher productivity.
That is, the productivity may be maintained constant in the mentioned application, not the pressure.
Am I wrong?


As the demand (water requirement) went up more pumps were added in parrallel.

Upto 3 skids it was fine but now we noticed that the pressure was fluctuating.

cheers.
 
You mentioned "4 quadraplex skids".... Do you have 4 independent systems? It sounds like you have 4 pump stations, each designed to function alone, but connected at the discharges, and all set to the same pressure. If this is the case, do the lag pumps sequence on based on 4 different PLC's all running the same program?

If so...... I agree that you need to take control of all 16 pumps with 1 PLC. And like DickDV said, 1 PID process loop controlling all 4 PLC driven pumps.

If you MUST "auto-equalize" the remaining 12 pumps, do it by storing "run time" for each pump in the PLC, and select the pump with the least time to start NEXT.

I prefer "auto-alternation" instead, which can be accomplished with a shift register or "ring counter".

Stationmaster
 
You mentioned "4 quadraplex skids".... Do you have 4 independent systems? It sounds like you have 4 pump stations, each designed to function alone, but connected at the discharges, and all set to the same pressure. If this is the case, do the lag pumps sequence on based on 4 different PLC's all running the same program?

If so...... I agree that you need to take control of all 16 pumps with 1 PLC. And like DickDV said, 1 PID process loop controlling all 4 PLC driven pumps.

If you MUST "auto-equalize" the remaining 12 pumps, do it by storing "run time" for each pump in the PLC, and select the pump with the least time to start NEXT.

I prefer "auto-alternation" instead, which can be accomplished with a shift register or "ring counter".

Stationmaster

Yes you are right Stationmaster.....they are 4 skids designed to work alone but now are running in tandem.

Hope the program (attached earlier is in the right direction..)

The running hours balancing is the tricky part...do you have sample program on that...?.

cheers.
 
Last edited:
No, I don't have a sample program for your application, but the principal is simple. You can accumulate seconds, (1 second clock pulse, plus pump "X" running, plus single shot, = add 1 to register "Xsec" for example), then "minutes", then "hours", for each pump. Equalizing "hours" is probably adequate, so you determine the "Xhours" register with the least "hours" using compare logic.

Because you have so MANY pumps, your process and program becomes large, but not impossible.

Consider instead though the alternative I mentioned: "auto-alternation". No mater HOW many pumps you have, it remains simple. Simply use a shift register to build a "ring counter" with 12 bits (1 for each pump). Shift the set bit by one position every time a pump starts. When it's time to STOP a pump because demand has been reduced, stop the pump that started longest ago. Your hours wont stay exactly balanced, but they will be close enough for most applications.

The OTHER benefit to auto-alternation is that if you send a pump out for repair, it won't ALWAYS be selected as the lead pump when it goes back in service until it's hours catch up like with auto-equalization. In a large system like yours, you ALSO want to make sure every pump runs once in a while to prevent rust build-up. Auto-alternation will guarantee this where auto-equalization will not.

I don't have the ability to open your sample program and text document right now, so I don't know what platform you're using. I'm trying to be "general" in that respect but give you some ideas. Hope it helps.

Stationmaster
 
Running them equal hours ( or nearly equal) has more to do with keeping the pumps in motion to avoid them getting stuck due to raw water scale on impeller and also to keep bearings in good condition.

Many a times a pump which is not being used for long will trip on overlaod due to the above mentioned conditions.

cheers.
 
Running them equal hours ( or nearly equal) has more to do with keeping the pumps in motion to avoid them getting stuck due to raw water scale on impeller and also to keep bearings in good condition.

Many a times a pump which is not being used for long will trip on overlaod due to the above mentioned conditions.

cheers.

No one said you should not exercise the pumps. Of course you should.

You can take solace in the fact that most will agree with you. It has been discussed some here before. Roy and I are in the minority. Not that big of a deal.
 
Last edited:

Similar Topics

dear all.. i am designing the Sea Water Intake pump which the 4 pumps will be operated parallel, and 1 pump will be as stand by pump The pump data...
Replies
3
Views
128
Hello Guys, I have tried the programming but can't twist my mind to make it work correctly. I'm using S71200 and TIA Portal. My system has...
Replies
1
Views
182
I have been reading everything I can find on the P_LLS the last 2 days but I am still having trouble understanding how the P_LLS swaps beyond 2...
Replies
9
Views
546
Hi, I started off my career in PLC programming doing water/wastewater on AB around 20 years ago, but then moved overseas a few years later and...
Replies
57
Views
11,866
Good morning everybody, I hope you are very well. I share with you the information of the PLC LOGO! Siemens and expansions that we have...
Replies
4
Views
1,058
Back
Top Bottom