load in parallel

[Greg80]

Hi...
A simple question but I cannot remember it
I have closed loop consisting of :
- a circulating pump.
- 5 loads in parallel

I know the system resistance curve and the pump curve .. and I know the operating point...

My question is I will add another load in parallel with small pipe run and low pressure drop (the pressure drop of this load is very low comparing to the other loads).

So I need more flow ..
I will add an additional pump to satisfy the flow rate required.

My question is : does the system resistance curve changes in this case ?

Thanks

 

[Greg80]

The question in other words...

Does the operating point of a pump will be affected if new parallel lines are added ?
These new lines have lower pressure drop than the existing ones.

00000 -------------------------- existing line
Pump -------------------------- existing line
000000 --------------new line (pressure drop lower than the existing lines)
000000 --------------new line (pressure drop lower than the existing lines)

I think the system curve will stay the same -- so the intersection point of the system and pump curve will be the same ...
Please correct for me if I'm wrong

 

[BigInch]

Sure it does. After all, you are adding another opening to the existing system. Pressure and flow will try to escape there, so it must go lower, showing you can get more flow with less pressure. That's why you need another pump, right.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[Greg80]

So the system curve will still the same but the operating point will change as the flow rate will increase ..
Is that right ?

 

[rneill]

Correct me if I'm wrong but you have a pump curve and a system curve and the operating point is the intersection of these two curves.

If all you do is add a new parallel line then the operating point must shift (lower pressure and more flow) but since the pump curve did not change (it is based on the physical characteristics of the pump only) this means that the system curve had to change in order to achieve this new operating point.

If you want to maintain the same system pressure (to satisfy the original lines) then you need to change the "pump" curve in order to move the intersection point of the new pump curve and the new system curve back to a point with the same operating pressure but more flow. In this case you might be able to tweak the existing pump (there is usually some room to change impellers or operating speed, etc.) or you could add another pump in parallel.

 

[BigInch]

Yes that's correct! The pump curve and all its parameters stay the same, the system curve's parameters will change and you will find each former head value moves to the right. The operating point will move with the system curve to the new intersection point.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/