Vertical pumps Showing lower individual consumption when working in parallel than when working alone 5

[Romesff01]

System - Take water from a well both pumps connected to a collector and booster pump to take water to destination.
Initial intention by building a collector - to increase the caudal of water at the end location and increase pressure at booster pump.

Why do I have a difference of consumption when using 2 vertical pumps in parallel?
Does it has to do with a collector not being well dimension?

 

[waross]

and increase pressure at booster pump.

And that seems to be working.
Look at your pump curves.
Higher pressure generally means a higher dynamic head.
That moves the operating point further up the pump curve resulting in less flow in each pump compared to running one pump only.
Less flow means less work is done and less power consumed by each individual pump.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Skogsgurra]

There's also the fact that you seem to measure amperes only. If you want to measure actual power consumed by the motors under different conditions, you should look at watts instead. You pay the utility for consumed kWh - not for ampere-hours.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Romesff01]

Thank you for you reply everyone.
1. No utility consumption I am running Generators outside of Grid.
2. although everything you said was corrected I am still wondering why is my Amperes Higher for the motors on vertical pumps. Individually their Amperes are higher however in parallel it seems like they are contain.
In other words why can´t I go higher on Pressure or Caudal when I have both vertical pumps working.

 

[Skogsgurra]

You still have to pay for the generator fuel?
But that was not my main point. If you do what Bill says. And then look at a Osanna/Circle diagram* to find out how your cos(phi) changes with load, you will understand.

If I had the time, I would take you by the hand and lead you through the steps needed. But I think that it is better that you do the homework on your own.

*This one is a good and useful one:

https://en.wikipedia.org/wiki/Circle_diagram

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Romesff01]

I believe I am not expressing myself well. My question has to do with me knowing if is possible that the pump-motor will be able to give more than is giving when in parallel.
This is not about energy consumption
I am just wondering if is possible that my system is restricting the Pump - Motor.
The system was created so we could use multiple machines at the same time, looking at the values I took I get the sensation that someone the system is restricting the pump - motor full potential.

 

[Romesff01]

Coting....
" When the mechanical load on the rotor is low the slip rate is lower, the back emf is higher, so the current allowed to flow is reduced (and the resulting power drawn is low). "

" When the mechanical load on the rotor is high the slip rate is higher, the current flowing in the rotor circuit increases, the back emf is lower, so the current allowed to flow is increased (and the resulting power drawn is high)."

 

[Skogsgurra]

The circle/Osanna diagram shows exactly that. Have a thorough look at it, especially how power factor changes with load, and do not assume that we do not understand what you are trying to tell us. In fact, the situation may be the opposite.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[VEBill]

"...both pumps connected to a collector..."

Would it help to consider what would happen if you had N of these pumps? All connected to the same collector. Where N is varied from 1 towards infinity.

When N is very large, each of the individual pumps would be flowing almost zero. Their outputs might as well be capped, when considered from the point of view of each pump.

"I am just wondering if is possible that my system is restricting [each] Pump - Motor."

Clearly yes.

It's just that N=2 is nowhere near N = infinity, but it's twice one.

All this barely qualifies as a first approximation, but hopefully it is aligned with a more detailed analysis as others have described.

It's probably a safe assumption that the relationships here (N versus your questions) are at least monotonic, meaning curves that are always headed in the roughly same direction.

 

[Romesff01]

we had 3 pumps-motor in the same collector, and we stop using all 3 because there was no noticeable increase of pressure or Caudal.

 

[Romesff01]

Agree. And thank you.
I was not disagreeing with anyone, in fact I was agreeing, since i have one f3ew information, i was asking if what i thought was actually possible looking at the information i posted.
Thanks everyone for the help

 

[waross]

The situation that you describe is normal for two pumps pumping into the same collector. Flow will generally be more, but not twice as much. With more flow from two pumps the dynamic head will be greater and at a higher dynamic head the output of each pump will be less.
I had one extreme case where 15 HP pumps were pumping sewage to a disposal field up on a mountain side.
The disposal field was moved higher up the mountain and the increased dynamic head pushed a single pump almost off the pump curve.
It was pumping so little that running 24/7 barely kept up with the flow.
When the second pump came online because of high levels the increase in dynamic head caused the flow through each pump to be so little that the pumps started churning. This heated the water to the boiling point. With the pump casings filled with steam instead of water, the flow stopped completely.
When the priming ports on the pumps were opened super-heated steam was released.
The heat of the super-heated steam burned the paint off of the pumps.
Your case is not extreme.
Your readings are normal for such a system.
As others have pointed out, the relationship between work done and current is not linear due to the power factor changing with the changes in the load.
However, more current generally means that more work is done.
Take a look at this explanation of pump curves.
Pump Curves
You will see that increasing the head, as shown by your pressure increase when two pumps are running, will reduce the required HP.
After your head increases past the Best Efficiency Point, The flow will also be reduced.
The comments concerning two pumps in parallel are correct but over simplified.
They are based on a constant head.
In your application, the dynamic head is greater when two pumps are working.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Romesff01]

Agree. But like I explain not even documentation of the pumps I have. That's why all my assumptions where base on test run of 3 vertical pumps, although I didn't put the values of the 3ª Pumps in there but yes you are right.
It´s never double but difference is noticeable.
I believe next step would be analyze the system to see if i can do something in order to use 3 pumps-motor and increase my pressure and thus increasing caudal of horizontal pump.
Once again thank you for all recommendations and knowledge it really helped

 

[waross]

Hello Romesffo1.
I have edited my last post to include a link to a pump curve tutorial.
But on reviewing your data it seems that with two pumps running, your pressure increases about 38% while your flow increases about 3%.
It looks as if you are operating much too far up the pump curves.
You should try very hard to obtain the curves for your pumps.
If you can supply us with the make and model of the pumps, we may be able to help.
It is probably not worth while to run two pumps in parallel without serious system changes.
First identify the bottle-neck.
Then try to correct that.
The 38% increase in pressure with two pumps is a strong indication that the collector piping may be undersized.
However the booster pump may be expected to deliver more flow if the inlet pressure has increased 38%.
We need a sketch of your system showing where the pressures are measured.
The actual head in meters between the water level in the well and the point where the pressure readings are taken will also help.
If possible send us the following information:
1. Vertical distance from the water level to the well head when one pump is running.
2. Difference in pressure between the well head and the inlet of the horizontal pump.
3. Pressure difference across the horizontal pump with one vertical pump running.
4. Pressure difference across the horizontal pump with two vertical pumps running.
5. A description of the discharge of the horizontal pump. Does it discharge into an open tank or pump into a closed system?
6. If discharging into an open tank, the vertical distance between the pump discharge and the discharge into the tank.
7. The horizontal pump discharge pressure when running.
8. Make and model of all pumps.
Yes, I know that this is a lot of work, but guessing at a solution that doesn't fix the real problem is worse.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[electricpete]

Good analysis and questions by waross

op: another things I was wondering:
You have two pumps in parallel and they're drawing substantially different current.
Are these parallel pumps and motors supposed to be identical in design?
If so, then obviously the difference in current is not expected. Suggests most likely one of the pumps is degraded.




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(2B)+(2B)' ?

 

[Skogsgurra]

Agree. A good strategy, it seems. PLS again.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[waross]

Pete and Gunnar. Thank you sirs. Stars are nice. Your kind words are much nicer.
Good point on the pumps Pete.
I noticed that but compare compare the discharge volumes when one pump is running.
186:170 M³per hr. Quite close. The difference may be different piping or machining tolerance on the pumps.
The data suggests that these pumps are operating so far up the performance curve that a very little mechanical difference may make a very large difference to the flow rate.
Note that when both pumps are running together, the pump with the highest current is hogging the load.
With one pump running, one pump delivers 9.4% greater volume. (186/170)
With both pumps running, one delivers an additional 6 M³per hr. (192-186)
and the other pump delivers an additional 2.5 M³per hr. (172.5-170)
Of the increased flow of 8.5 M³per hr, one pump delivers 70.6% and the weaker pump delivers less than 30%.
When the pumps are operated that close to cutoff, a very small mechanical difference will make a very big difference to flow and energy use.
I suspect that at 50% of the present head, both pumps would match performance within 1% or 2%.
But, like you, I at first noticed the current difference.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[waross]

Romesff01;
A proposed solution.
First let me mention again my similar problem.
The head was approximately double after the change.
The pumps were not submersible. A pump shop mounted a belt drive pump and a 30 HP motor.
The motor sheave (pulley) was a little bigger and ran the pump a little faster than the motor.
This developed a higher cutoff pressure. The ratio was well calculated and the 30 HP pump gave comparable performance to one of the 15 HP pumps at 50% of the head.
You obviously cannot belt drive a submersible pump, but you can make it turn faster.
The maximum pressure or cutoff pressure is limited by the diameter of the impeller and the square of the speed of rotation.
Raising the speed and the cutoff pressure has the effect of moving the pump down the pump curve to a much more favourable operating point.
With the pumps that far up the curve I suspect that the current is quite a bit below the rated current. I anticipate that you will be able to deliver enough water with one pump.
Yes, a VFD will be expensive. Any other solution may be less effective, and any other good solution may end up costing more than a VFD.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Romesff01]

I wish I had but I am dealing with very old pump-motor and everybody saying that the documentation was lost.

 

[Romesff01]

I will see if I can get something from the tags.



----------------------------------------------------------
waross (Electrical) 8 May 19 17:59
Hello Romesffo1.
I have edited my last post to include a link to a pump curve tutorial.
But on reviewing your data it seems that with two pumps running, your pressure increases about 38% while your flow increases about 3%.
It looks as if you are operating much too far up the pump curves.
You should try very hard to obtain the curves for your pumps.
If you can supply us with the make and model of the pumps, we may be able to help.
It is probably not worth while to run two pumps in parallel without serious system changes.
First identify the bottle-neck.
Then try to correct that