No tank irrigation system.

[DallasT]

I am installing an irrigation system supplied by a submersible pump. the well was just recently drilled and is producing 45gpm at 74 feet total depth is 125 feet. I am installing a 3hp 27 gpm pump. I know what the pump and delivery requirements are but I'm not sure how to plumb it without a pressure tank. The system will be powered by a generator tied in to a breaker box through the controller to the pump. Similar systems we have installed that free flowed to either irrigation or to ponds did not have pressure switches or low pressure cut out switches installed. They were manually operated and monitored during operation. There was no concern of over pumping. The wells were running 5hp pumps pumping 85 to 100 gpm at 50 feet. They regularly run 72 hours straight. Since this well is new I'm concerned of the possibility of over pumping. Should I install a low pressure cut out switch and how do I plumb it without the tank? Can I cap off the tee that feeds the tank and still have a switch, gauge and pressure relief valve on the tee? any input recommendations or suggestions would definitely be appreciated.

 

[Valveman]

You do not need a pressure switch if you are manually turning the pump on and off. Just connect directly to the sprinklers. I would add a 75 PSI relief valve just in case the pump comes on and no sprinklers are left open. In this way the pressure will be determined by the number of sprinklers are being used. You can still use a Cycle Stop Valve on a manual system and it will maintain 50 or 60 PSI constant down to as little as a 3 GPM zone.

The 3HP, 27 GPM pump is made for a much deeper well. A 50 GPM, 3HP will give you 60 GPM from 125' total head and is much better suited for such a shallow well.

 

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[DallasT]

Thank you Valveman for the information. Maybe I chose that pump for the wrong reason. I wanted something that could deliver the volume I needed to cover two acres but not over pump the well. This is a new well so I don't know for certain what the actual continued capacity will be. As a safety measure should I install a low pressure cut out switch? If the pump is running unrestricted free flow and the well runs out of water will the pump continue to run if there is no kind of limiter installed in the system?

 

[Valveman]

40 PSI for the sprinklers adds 92' of head to the 74' pumping level for a total head of 166'. At 166' of head a 2HP, 25 will pump about 35 GPM and a 3HP, 40 will pump about 47 GPM. You cannot use a low pressure cut off pressure switch without using a pressure tank. Even then a low pressure switch is not a reliable way to protect a pump from running dry. The 2HP can use a Cycle Sensor to protect the pump from a dry well. But we no longer make larger Cycle Sensors for 3HP and larger. But you could find a Symcom, Littlefuse, or other brand of pump protector that uses amps instead of pressure to protect the pump/motor.