3 Pump Irrigation Setup - Double checking my plans

[garugaga]

Hello Cary,

I recently retrofitted a CSV3B2T in our greenhouse so we could have constant pressure instead of manually turning the pump on and off when we needed water. Other than some pulsing issues that I hope to have under control now it's working great.

Now that springtime is upon us I would like to get our outdoor production on constant pressure and am looking at a cyclestop solution after it worked so well in the greenhouse.

This year we are upgrading to 2 10 HP pumps and 1 5 HP pump. At our location we only have single phase power available which is why we can't get a motor sized larger than 10HP.

We have 2 separate fields that each will have a 10 HP pump dedicated to them with the 5HP handling the constant pressure on a pressure switch and being behind a cyclestop.

I know that you recommend that each pump have it's own cyclestop valve but I think that I will be able to get around that because the 10HP pumps will be called on via our irrigation computer and not from a pressure switch.

The 5 HP pump will not be used for mass watering, it will only be used when we are hose watering.

This is an image of what I am planning on building: imgur.com/a/UvAcm (you'll have to copy and paste, I'm not allowed to post links)

I will run the 5hp pump on a relatively low pressure, maybe 35-50 on the pressure switch with the cyclestop holding pressure at 40 PSI.

The 10HP pumps build 60-65PSI and when we are mass watering they never drop below 50 PSI so the pressure switch should never cycle the 5 HP pump while mass watering.

The main reason why we are doing it this way is to save our 10HP pumps. A 10 HP single phase motor really shouldn't be ran for less than an hour, with our irrigation computer I can guarantee that in it's logic.

Also, we will never need the 10HP unless we are running the irrigation valves and we never run the irrigation valves without the irrigation computer so there's no need for them to be pressure controlled.

Also, I am very price sensitive and 1 $1000CAD valve is a lot more easy to sell to the powers that be than 3 $1000CAD valves.

Do you see any potential roadblocks with this install?

[Cary Austin]

As long as the irrigation controller turns on enough sprinklers to exactly match the output of the pump it will work.  However, a 10HP at that pressure will pump maybe 150 GPM.  So you will probably have considerable water hammer when starting and stopping those pumps at 150 GPM.  A CSV would make each pump start and stop at 5 GPM, not 150 GPM, which eliminates any water hammer.

Normally $1000 for a 3" and $647 for a 2" CSV is considerably less than a bunch of large pressure tanks or a VFD controller.  Having a CSV on each pump is still an inexpensive way to control the pumps and eliminate water hammer.  I find that 50 GPM or so pumps can work off a pump control relay or an irrigation timer.  But anything larger than 50 GPM usually causes a lot of water hammer when starting or stopping the pump.  It doesn't take too many broken lines from water hammer to make a CSV on each pump seem very affordable.