Pumps in series

[mfqd13]

Hi,

I have a specific situation to study but i would like to receive some opinions and i will put the question in a very basic way so that i can start from scratch.
I've attached a pdf file with a simple drawing.

Assumptions:
- Both pair of pumps are working at 50Hz
- Each pair of pumps has equal pumps but the 1st pair has different pumps from the 2nd pair.

Questions:
1) If i have the 1st pair of pumps with a greater nominal (catalogue) flow than the 2nd one witch will be the flow passing both groups? (forgetting that bypass line iwth the second consumer)
2) Assuming that exists that bypass line with a 2nd consumer, what will happen in this situation? What should be the flow in this by pass line?

I didn't put any numbers so feel free to put some to give examples.

Thanks

 

[mfqd13]

I forgot to attach the file...

 

[TD2K]

The consumers set the flow, the pumps (assuming these are centrifugals), simply move to the appropriate spot on their curve.

Let's say the consumer after the first set of pumps takes 100 units/time. The second consumer also takes 100 units per time. The flow through the first pair of pumps is 200, 100 goes to the first consumer and 100 goes to the suction of the second set of pumps. The pump curves will tell you the resulting pressures.

Typically, there's something like a surge tank on the suction that sets the pressure at that point but you'll need to look at your point.

 

[mfqd13]

Ok, so let's say that the 1st group of pumps as a volumetric flowrate of 200 m3/h and the 2nd group of 100 m3/h.

Now, look at the new diagram (in attachment) where the 2nd consumer was substituted by an open tank.
What should be the flowrate going through this line to the opened tank? It depends on the head avaiable at the outlet of the 1st group of pumps, correct?

Thanks!

 

[TD2K]

Maybe we need to define the terms we are using. When you say the flow rate of the first group of pumps is 200 m3/hr and the flow rate of the second group of pumps is 100 m3/hr I'm assuming that is the total flow rate. By conservation of mass, the flow to the open tank has to be the difference, 100 m3/hr.

If the 200 m3/hr and 100 m3/hr are the pumps' rated flow rates and they are centrifugals, that's another question and you can't solve it with the information you've got.

 

[mfqd13]

Sorry, i was talking about the nominal flow rate capacity of each pair.
Of course, if the 2nd pair in operation mode only works with a flow rate of 100 m3/h the 2st pair will adjust it's working point in the curve, but i was talking about the nominal capacity.