Related to Flow Summation

No

I am assuming this is about centrifugal pumps pumping water.

The increased flow in the delivery line will mean increased friction and therefore the duty pressure of the pump will increase.

If you have a look at the pump curve you will notice that the delivery would be less to deliver against the higher head. The individual delivery of combined pumping will therefore be less.

You will also notice that the efficiency would be less (if the single pump well selected) It may even be advisable to rather have a bigger pumping to deliver the desired flow.

Exact changes can be calculated if more info is known.

If the discharge line is infinite diameter or zero length, then the flows will simply sum...

I believe we, at KrisDel ^TM Products, have such a pipeline in stock.

Del

Would that be the pipeline stock with the internal groove for increased velocity or the one with the external groove for increase heat transfer to the air?

Any chance that the hole in the pipe is on the inside....

If I understand the question correctly, I need to disagree with Hendrik. You are stating that you have a flow transmitter on each individual pump as well as a flow transmitter on the main header. Lets ignore the fact that this is seldom seen in practice because it is a waste of money to measure both individual pumps and the entire system. On multi-pump systems you are typically only interested in the total flow unless the two pumps draw from separate systems and even then you would only meter the individual pumps and not the main header. Why? Because they would need to be the same. Basic mass balance says that with no accumulation, input equals output. The sum of the two pump flow meters must equal the flow reading of the header flow meter. Any difference between the two would be in the instruments themselves not in the actual flow. This is another argument against double metering. The question of which one is right. The discharge pressure has no bearing on the question.

Now, if the question was if each pump were run individually and produced a certain flow, would these pumps produce the same flow if both were run at the same time, the answer would be no as Hendrik explained.

I am curious if there would be loses at the point of confluence as to effect some small back-pressure on the pumps and therefore cause a reduction of the pump efficiencies or discharge flowrate, and consequentially reduced combined output from the rated?

Here is another way of looking at Hendrick's argument I think: Transform the situation into its Electric circiut analogue in which the pumps are EMF and the flowrates are related to currents, now will the increase in current at the common circiut line cause an increase in resistance (pressure) high enough to reduce the amount of current flow? Now keep in mind that the electrical resistance R of a wire increases with Temperature, and the Temperature increases with higher current flow.

Just a thought

Dear Andrew,

The Pumps are identical in both the working and specification. You dont need to worry about that. My problem is only with the TX, as the discharge pressure of both the pump are identical and the service in both the pump are also same (diesel), even the discharge pipe line's diameter is same as the common discharge line's diameter.My question is will the common discharge flow will be the summation of the individual pump's discharge flow? Clarify?

Andrew is right, You should check the meters and installation in case of any discrepancy.

Just a few more options.

Two identical pumps in a dual system may deliver different flows. This may be because of slightly more wear on one pump, Tolerance discrepancies, different piping, or malfunctioning valves. rpm variations, bad drive etc.

With only one pump in operation the flow will be more than halve (unless a flow restrictor is present) This is because of less friction in the delivery line. A single pump may consume more power.

Please give an indication what your problem is.

Rhetorical question - if one put two batteries in parallel, would one get twice the current? The answer is no, because the system characteristic needs to be taken into account.

The flow will be somewhere in the middle of 350m3/hr and 700m3/hr, and the system characteristic, together with the two pump curves, will determine exactly where.

Dear RAJU

Individual passes flow sum equal to main head flow. you will get som small +/- error it is not big issue because this error will come due to calibration error and transmitter efficiency.

OK Thankyou

RAVIVARMA

I agree with Andrew on this. The questioner didn't describe the individual pumps, only their Flow TX's. The pumps may be totally different pumps. One could be 100 GPM (I'm in the US) and one could be 200 GPM. Both pumping into the same line they would definitely not deliver 300 GPM together. The individual meters could be used to see what each pump does individually as opposed to the total flow. But whatever each individaul meter reads, they will, indeed, total the flow as displayed on the common meter. This is, of course, assuming that the three meters are accurate.

Dear concern,

The Pumps are identical in both the working and specification. You dont need to worry about that. My problem is only with the TX, as the discharge pressure of both the pump are identical and the service in both the pump are also same (diesel), even the discharge pipe line's diameter is same as the common discharge line's diameter.My question is will the common discharge flow will be the summation of the individual pump's discharge flow? Clarify?

Actually, no. The indivudual pumps running alone will not pump the same amount with both pumps running. Let's say that Pump #1 pumps 500 GPM alone. Then you turn #1 off and turn on #2. It also pumps 500 GPM by itself. Now you turn on both pumps. The flow can never equal 1000 GPM with both pumps running under the same conditions. Each pump, assuming as you said that they are identical, will contribute half the total flow, whatever that may be. If the flow with two pumps running is 850 GPM, each pump will be delivering 425 GPM. You can verify this by observing the individual flow meters that you have installed. Each should be pumping the same and these two should equal the common flow meter. This, of course, is in theory. Little differences in the manufacture of the pump itself, imperfections in the inside of the piping, all these can make a difference in the flow coming from each pump. However, if you are within a few percentage points of one another, you can assume they are equal. That, is not precise engineering, I know, but it is reality.

At the risk of beating a dead horse, the flow in the common discharge pipe must equal the sum of the individual pumps. If, in the course of one minute, each pump pumped 200 gallons of fluid, the common header must also show that 400 gallons has passed. Otherwise, where did the extra liquid go? Please don't focus on the discharge pressure, it must be the same on each pump as it will also be the same as the discharge pipe if they meet close together. One thing that does concern me is that the discharge pipe is the same size as the individual pump discharge pipes. Typically the pump pipes are smaller than the common header as they will not be expected to pass as much flow.

The Answer is still a varible as the pumps as much as we would like are not identical and the power provided by the motive force will also fluctuate but with that considered the pumps can be additive but I have seen a pump become dead headed as the sister pump provide near 80 percent of the total flow. refer to the pump curves as indicated when reviewing the flows and only if you measure at the discharge of the pumps ahead of the check valves will you know what each pump is flowing. Again small changes in impellers and HP in the driver will not allow the flow equation to be 1/2 of the flow distributed to each pump. But running each motor individually will deliver nearly the same flow at a measured pressure.