Two Pumps in the same well

[Tom101]

I have a well that supplies water to a dormitory for college students.  I only have one well with 12" casing and about 400' deep.  The pumping level is about 300' and the static water level is 220'.  My problem is that most of the time the dormitory will be using an average of about 30 GPM but, during peak times could use as much as 400 GPM.  I need to install a pump that will deliver 400 GPM at 70 PSI but, most of the time the dormitory will be using less than 30 GPM.  I know that when controlled with a Cycle Stop Valve it will not hurt my pump to vary the flow from 5 GPM to 400 GPM.  However, this will take a 75 HP submersible which will only drop to a 40 HP load when restricted with the CSV.  Is there anyway I can get a second pump to fit in this same well so I could be using a 7.5 HP pump for low flow and still be able to use the 75 HP when needed?

[Jeff Fletcher]

To put two pumps in the same well where the casing is not large enough for two pumps to hang side-by-side, you will have to use a Wesly Tool. This adapter allows you to hang both pumps on the same drop pipe. The smaller pump will hang on the drop pipe above the larger pump. The 4" Cycle Stop Valve(CSV) and plumbing at the top of the well is the same as a normal installation with one exception. You will need to install a 1.25" by-pass around the CSV with a solenoid valve and a ball valve. This by-pass allows us to set the minimum flow for the larger pump so it will allow this pump to shut off when the flow can be handled by the smaller pump.

Typical settings will be as follows. Pump#1 (7.5 HP) pressure switch settings ON 70# Off 80# with low pressure cut off switch set at 55#. Pump #2 (75 HP) pressure switch settings ON 65# Off 85# with low pressure cut off switch set at 55#. The pressure tank should be pre-charged to 50# and the pressure relief set at 90#. With these settings this is how it will typically work. The pumps are in a no flow condition and you start using 15gpm. The pressure in the pressure tank drops from 80# to 70#. At 70# the pressure switch for pump #1 starts the 7.5HP submersible.  The CSV is set at 70# and the valve regulates and holds 70# steady. The CSV will hold this pressure until the system uses more water than the 7.5HP can provide which is approx. 45-50 gallons . When more than 50 GPM is being used the pressure drops to 65# and the pressure switch for the 75HP closes which starts the 75HP pump. When the 75 HP starts a relay will cut out the 7.5HP and energize the solenoid on the 1.25" bypass which will be set to flow 30gpm. The system was requiring over 50gpm when the pressure dropped enough to start the75HP. The minimum flow through the bypass and CSV is now 35gpm. Because system usage is over 50 gpm the CSV will hold the system pressure at 70#. When the system usage drops below 35gpm the bypass will allow the 75HP to build pressure to 85psi and the pressure switch shuts off the 75 HP pump. Since there is still usage in the system the pressure will quicly drain the tank down from 85 psi to 70psi and the 7.5HP will come on and take care of the low flow conditions.

System settings overview.
Cycle Stop Valve set at 70psi
Pressure tank pre-charge 50psi
7.5HP Pump #1 Pressure switch On 70psi Off 80psi
#1 Low pressure cut off set at 55psi
75HP Pump #2 Pressure switch On 65psi Off 85psi
#2 Low pressure cut off set at 55psi

We can provide drawings, pictures, and wiring schematics to help you understand the process a little better.

Hope this gives a general understanding of the way we can do this.

Call or email if you have any questions.

Jeff Fletcher
800-652-0207

[Tom101]

Thanks Jeff!  That makes sence.  What is a low pressure cut off used for?

[Porky Cutter]

Wow, I never thought of that, however it's quite simple when you think about it.

[Dennis Haney]

Example Drawing

[Porky Cutter]

A drawing is even better. Thanks.

[Cary Austin]

It seems simple when you see a picture and hear it explained so nicely, but a lot of thought goes into keeping it simple and making it work so beautifully.  My hats off to Jeff for making this work so well.  I hear the customer is happy and basically says he hasn’t had to give the water supply a second thought since start up of the system.  Maybe Jeff can get us a picture of the installation and possibly a few words from the operator or owner?  Good Job!

[Ron Kyger]

Here is a picture from the installation. It shows the bypass that Jeff had specified and the valve. The installation was done in a vault.

[Cary Austin]

Thanks for the picture Ron.  No news is usually good news but, have you heard anything from the people at Wala Wala College about what they think about the performance of this system?

[Ron Kyger]

I agree, no news is good news. I haven't heard anything from them. I will be checking in with them in a couple weeks when I am down in that neck of the woods. Last I heard, they were fighting the soft start ramp time on the big pump. If the demand was too much too fast, the pressure would fall off significantly before the big pump ramped up to speed.

That picture turned out all right for a camera phone, huh?