Parallel Vertical Turbine Sump Pump again...

Ok, Here is what I have 2 sump pumps in parallel. 1250 USGPM each. operation right now with (65 psi - 0 psi)*2.31= 150 ft Head (if my calculation is correct.. there is no supply pressure because it is pulling from a sump, right??). Now what is my estimated FLOW RATE from this configuration as it sits??? I appreciate your help because again, I am no pump expert... I realize I could get this info of the pump curves but I only need a rough estimate and I think that 1250 GPM X 2 = 1500 GPM is too rough an estimate.

CAF

 

Of course, I meant 2500 GPM on that last calc.

 

[electricpete]

I'm assuming you don't have the ability to measure gpm, but you have nameplate info from the pump.

If so, I think that anyone who answers will require some additional info to estimate what 1250GPM is based on. Is there an associated total head? Perhaps a horsepower rating?

Also to get a little more accurate we would want to consider what is the fluid density (this changes the dp for a given volume flow-rate) actual and assumed by the manufacturer, what is the speed actual and assumed by manufacturer, and pump suction elevation assumptions.

 

How and where do the pumps discharge? And yes the sump is supplying pressure, if it wasn't, then the pumps would not be in the liquid....

Bob

 

i'm a beginner here and have a simple question:
is a sump pump a centrifugal pump?
any help...thanks in advance.

 

[stressriser]

You really are not going to get the answer to this question on this forum, you are going to have to do some work. I see two options:

1) You need to combine the system curve with the pump curves. Usually the two pumps are not the same size. You really need to look at a graph to understand. Capacity will not increase at heads above the maximum head of the smaller pump. A second pump will only operate when its discharge head is greater than the discharge head of the pump already running. At a point of equal pressure, the two pump curves join as a combined flow rate, the intersection of this combined flow meets a point from the system curve for total output. You need all four curves.

2) Measure it yourself. Find a nozzle, there must be a drain or fitting somewhere that you can tap into. Start both pumps, fill a bucket, time how long it takes to fill, weigh the water and then calculate into gallons. Look up the weight of water at a specific temperature if you need to be that accurate, but then again you shouldn't use this method if you need that much accuracy.

The depth of the water supplies pressure. Every inch of water supplies an inlet pressure to the pump. Since this is a sump pump, I imagine that the water level changes. (?) So the supply pressure will drop as the water level lowers.

Also, we are assuming that the pumps discharge into a common header. Otherwise they are not in parallel, they would be considered separate systems and you could add the two together as you are trying to do. If they do in fact discharge into a common header, you need to look at the curves or make the measurement.

The pump curves come from the manufacturer of the pumps. The system curve comes from the engineer that designed the system. The system curve is usually done first to choose the pumps. The system curve also depends on a constant pressures, so if the water level is dropping at the pumps, this curve gets hard to follow. In this case, the lower water level will have a system curve, and the higher water level will have a system curve. These two curves will intersect the pump curve at two diffrent points indicating the extreme operating points, and yes, two different flow rates. If you add another pump curve to this, you are going to have a multitude of flow rates at any given time, depending on the water level of your reservoir. What happens when you put two pumps in parallel, of the same size, is that the curve flattens out, thus making the system a little more reliable when system demands change.

I'm sure I have only confused you, but I think this proves Bob's point that he makes so often... get an engineer to help you.

 

[JeffHofacre]

I am assuming this system was designed for only one of the two sump pumps to be running. The discharge piping is common to both pumps. A check valve is installed after each pump. Therefore the pressure drop of the discharge piping was likely designed for the 1250 gpm flow case. If this is correct you will not get double the flow when you start the second pump. You may get 1400 gpm, 1800 gpm, even 2000 gpm, it all depends on how the system resistance.

If you truly want double the flow you need to have a separate discharge pipe for each pump.

I agree with stressriser's comments.