Delta-P and flow in a series pump circuit

[stc4025]

I am trying to solve a flow issue with our mold coolant system. I know that the higher the Delta-P in a closed single pump system the better your flow. If you were to take the discharge of that pump and plumb it into the inlet of a second pump in-turn connecting the second pumps discharge in to the inlet of your initial pump does the Delta-P theory invert? The lower the Delta-P the lower the restriction in the system increasing your flow in the circuit?

STC

 

[trashcanman]

" I know that the higher the Delta-P in a closed single pump system the better your flow."

Please explain how a higher pressure drop makes the flow better. All it does is increase pumping power requirements and possible create noise.

For pumps in series, the flows are equal, the heads developed are additive.

The lower head the pump sees, the more flow it can produce. Look at the pump curve.

 

[ChrisConley]

To add to trashcanman's comment: if you need more flow (and are adding a pump) you need to add the pump in parallel to the original pump.

Other ways to increase flow in the system are to decrease resistance in the system, increase the speed of the pump, or add a larger impeller.

 

[stc4025]

I should have phrased that better. My engineers are telling me that the higher the delta-p the better and more turbulent the flow. My question is in relation to the secondary pump that I have installed on the machine to increase flow with the resources that I have available. I have a double parrallel pump closed loop system that is divided into 16 individual lines at every machine. With only the machine I was working on open to the system I wasn't acheiving the flow that they wanted to see in the individual line "8gpm". I was only seeing 2.4gpm. If both pumps were on and the pressure was increased to 125psi on the discharge my flow became 3.6gpm After extensive replumbing in the machine I saw a very slight increase in flow. Slight meaning I could have read the meter from a different angle and achieved the same progress. I then took a 7.5HP pump and plumbed it in series with the other pumps on the outlet side of the molds, effectively drawing the water through the molds and forcing the discharge up the return line to the main return header,to overcome any restriction they may be present in the machine and return line. I worked beautifully I increased the pressure from my primary pump to 125psi and my gpm jumped to 7gpm. Over the phone they were ecstatic. Upon looking at the machine they got all flustered that the delta-p had diminished, "we need to increase your delta-p to increase the flow" I was then told. Having a 55psi delta-p that had diminished to 15psi. I explained to them that I believed that the series pump would invert the theory on that. As the pressures in the system equalize the flow is increased and the restrictions are overcome. What are your thoughts?
Thank you
STC
Attached is the initial tests I did on the system. The setpoint is a diff pressure controller on the pump skid.
I didn't have time to do extensive testing on the new arrangement before they took it over.