Irrigating From Three Different Pumps

[Tom101]

Dear Dennis Haney.  Someone at your office said you could help me.  I have three pumps in different locations that feed into the same irrigation system.  One is a centrifugal pump, 5 HP DHJ Sta-Rite, that draws water from an irrigation ditch.  Another pump is a 70 GPM 5HP Sta-Rite submersible in a well that is about 80' deep.  The last pump is a 3 HP Goulds  33GS30 submersible also in an 80' deep well.  How can I make these three pumps work together and supply any amount of flow required by the homeowners?  I need at least 50 PSI on the system.  One problem is that the homeowners could open up too much water.  If pressure from the 70 GPM well pump is too low. The pump produces 100 GPM and the well starts making sand.

[Dennis Haney]

Tom101,

To incorporate three pumps in different locations into one system, all you need is:

A Cycle Stop Valve per pump
A pressure tank per pump
An on/off pressure switch per pump

In your application, you will also need a low pressure cut-off switch for each pump.  If you open up so much water that pressure falls to 40PSI, then the low pressure switchs will turn off the pumps keeping them from pumping sand.

Let's call the pumps as follows:
33GPM 3HP submersible - Pump 1
70GPM 5HP submersible - Pump 2
5HP centirfugal - Pump 3

Pump 1 - use a CSV2W 1.25T 50-120 Cyle Stop Valve set at 70PSI
Pressure switch set at 70PSI on / 80PSI off
Low pressure cut-off set at 40PSI

Pump 2 - use a CSV3B2T Cycle Stop Valve set at 60PSI
Pressure switch set at 60PSI on / 70PSI off
Low pressure cut-off set at 40PSI

Pump 3 - use a CSV3B2T Cycle Stop Valve set at 50PSI
Pressure switch set at 50PSI on / 60PSI off
Low pressure cut-off set at 40PSI

When you start using water, pressure in the tank will drop from 80PSI to 70PSI and start pump 1.  If you open up more water and pump 1 cannot keep up, pressure will drop to 60PSI and start pump 2.  Open up even more water and pressure will drop to 50PSI and start pump 3.  This ensures that you will always have at least 50PSI on the system.  
Close off water, and system pressure will climb shutting off the pumps accordingly.

If the pumps shut down on low pressure, they will have to be manually re-started.  This means that the water usage will have to be closed off and the low pressure switch on pump 1 will have to be bypassed so that the pump will be able to start and bring system pressure above 40PSI.  Some switches have this bypass feature built in, but some do not.  For the switches that do not,  a simple light switch or toggle switch will work.

In selecting the pressure switches, you need to pick a switch that will allow a 10PSI differential between on and off.  Exapmle: on at 50PSI - off at 60PSI.  

Please see below for how this will look.

Thank You,

Dennis Haney
Cycle Stop Valves

[Tom101]

Thanks for the drawings and explanation.  Two more questions please.  Only Pump #2 has a problem of pumping sand if the pressure gets too low and the volume too high.  Is there any way to just keep this pump from over pumping the well and not have the entire system shut down on low pressure?  Also those pressure switches that work at 10 PSI bandwidth are expensive.  Is there anyway I can use the old Square D FSG-2 switches that I have?

[Dennis Haney]

Yes,

By overlapping the pressure switch settings,  and using a CSV3B2T with a BPPA feature on Pump 2, we can accomplish the same thing.

BPPA stands for Back Pressure Pilot Assembly.  This is just a sustain pilot plumbed in conjunction with the regulating pilot on the Cycle Stop Valve.  The BPPA will ensure that a constant back pressure will be held on the pump.  In your application, 60PSI.  In other words, all the 70GPM pump will deliver is what it can at 60PSI .

Set the pressure switches / Cycle Stop Valves as follows:

Pump 1 - On at 65PSI  / Off at 80PSI_CSV at 70PSI
Pump 2 - On at 55PSI  / Off at 70PSI_CSV at 60PSI_BPPA at 60PSI
Pump 3 - On at 45PSI  / Off at 60PSI_CSV at 50PSI

You might want to consider using a Cycle Sensor on Pump 3 since you did away with the low pressure cut off protection.  Just in case the irrigation ditch runs dry.

Try this link.
http://www.cyclestopvalves.com/products.html#cyclesensor

[Cary Austin]

Excellent post Dennis!  Your explanations and drawings are very well done.  I’ll be looking for this in our competitors installation instructions very soon.  Too bad it will never really work with their slow reacting, fully closing type valves.