well field pump sizing

[drain]

I'VE POSTED THIS ALSO IN THE PIPING FORUM.
Does someone with experience in parallel pump operations, using well fields and two discharge heads have time to look over my procedure below and comment. Or direct me to resources where I can check myself. I haven't done a parallel operation with 2 discharges before and may have missed a few steps. Thanks for your precious time.

My data is below for use of two constant speed pumps discharging directly into two tanks:

Well #405 -- rated Q = 175 USgpm, static lift range 440 - 525 ft

Well #407 -- rated Q = 250 USgpm, static lift range 395 - 450 ft

Both connect to a common main some 500 ft downstream, then discharge to two tanks at different elevations. Here's what

Planned procedure is as follows:
1)calculate suction and discharge losses up to the manifold for each pump. Plot separately.
2) calc losses for combined flow from manifold onwards to each tank with high and low C-values
3)plot max and min system curve for static lift range from manifold to discharge for combined flow, then superimpose on plots in 1)
4)Add the pump curve to each plot, then subtract the losses in 1) from the pump curves to re-plot pump curves (explained in Pumping station design, 2nd Ed)
5)Add revised pump flows together to create a curve for combined pumps
6) determine operating points for each pump individually, then combined
7)check that pumps are working at 80% of shut off head

 

[Kawartha]

drain,

I assume that this application is 2 water wells, with either vertical turbine or submersible deep well pumps. Please confirm.

Why do you have such a wide static head range (85' in one case and 55' for the other). Is this because of the change in well water level after pumping starts? You should really analyse the system based on drawdown levels in the well (highest static head). This should be based on the recharge capability of the well. In other words, the static lift should be based on the long term liquid level in the well during pumping (at the design flow rate for each well). The performance of the well will be provided by the well driller during development of the well.

With the potential flow rate from each well, calculate the head loss in the piping to the header for each pump. Then calculate the total head from the header to the 1st & also to the 2nd tank, based on the flow to each tank. Adding the static lift to the overall friction losses will provide the head required for each pump.

Make sure that you provide pressure gauges at each pump discharge (also at the manifold) and butterfly valves (or other valve type) to ensure the correct flow from the wells (this will control where each pump operates on its individual performance curve). You will also want to provide flexibility for changes in well performance as the well productivity changes over time.

You will have to check operation for one pump (or the other) only in operation to ensure the pump will operate on its curve.

I'll try to respond to comments which you may have.

 

[drain]

Kawartha
2 water wells. submersibles. Static range is from two factors: 1) we're pumping to two tanks vertically separated by about 40 ft, and 2) I've approximated the variation in drawdown vs pumping duration from what driller recorded during testing in order to estimate a change in available suction head.
I've also been wondering if throttling will occur if I put a 250gpm pump in well 407 and a 175gpm pump in well 405. Both meet the manifold about 500 ft downstream.
Thanks.
drain

 

[drain]

Kawartha

Now back in the office and can give you better info.

Well # 405 407
Fixed elevations, feet Grade 351.1 377.3
Pump intake below grade -229.7 -178.8
Below grade water levels Static -9.8 -9.8
During pump test 3 hrs -49.2 -31.2
12 hrs -82.0 -37.7
2.8 days -114.8 -45.9
High water elevations Tank 751.3 751.3
Pond 788.8 788.8
Low water elevations Tank 739.9 739.9
Pond 785.5 785.5
Flow rates, usgpm during pump test 150 120
Hydrogeo recommended 175 250

Unfortunately, long term yield recommended by hydrogeo has not been tested although the fractures are 30 ft and 10 feet.

Thanks a lot for your help.

 

[Kawartha]

drain,

I need a little time to think about your application, so will probably not be able to do a thorough review for a couple of days. In the meantime I would consider the friction losses in the discharge pipe from the manifold to the highest tank. The friction losses between the 1st and 2nd tank should be based on the expected flow rate to the 2nd tank. At tank #1, I would install a control valve (butterfly probably) for flow control into tank #1.

This means adding the friction losses for Pump #405:
a) from pump #405 to the manifold at design flow,
b) from manifold to Tank #1 based on design flow for both pumps,
c) from Tank #1 to Tank #2 based on the design flow rate to tank #2,
Add this to the total static lift (lowest expected water well elevation to highest Pond elevation.

Do the same for Pump #407, also at your design flow rate. Use the same friction losses for manifold to the Pond as calculated for Pump #405

Hope this makes sence.

 

[drain]

KAWARTHA
If you're interested and have the time, I oculd email you the spreadsheet with the system curves.

Tom (DRAIN)

 

[Kawartha]

Tom,

I'll try to have a look at the spreadsheet this weekend. Send to rburri@pathcom.com. Try to send it tonight or early tomorrow morning because I am in the process of changing to high speed connection tomorrow.

Regards,

Richard