Pump start water hammer on wellhead sprinkler

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Rusty123

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My house is on a private well. 3/4 hp submersible pump, 20 feet static head, 80 gallon pressure tank.

Lawn sprinkler system is teed off wellhead. Soon after buying the house, I noticed severe water hammer and pump cycling when sprinklers were running (neither of which occurred with indoor fixture use). I strongly considered installing a CSV to reduce the cycling (I even bought one), but first I decided to change out sprinkler inserts to increase flow. After lots of experimentation, I was able to balance sprinkler flow with pump output for all zones, which resolved the excessive cycling.

But I still get a pretty severe water hammer when the sprinklers activate and the pump starts for the first time. I suspect this is because the initial sprinkler flow causes the water to flow from the pressure tank out of the house, and the pump start causes a sudden flow reversal into the house.

I’ve thought about installing a pump start relay (in addition to the pressure switch) to force the pump to start as soon as the sprinklers activate, but I’m leery of a sprinkler zone failure causing the pump to run continuously and over-pressurize or burn up.

Any other solutions?
 

Valveman

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You probably have a check valve above ground. Remove that check valve and water hammer on pump start will go away.

Oh, and your sprinkler zones SHOULD be set to keep the pump running continuously. It is the cycling on and off that will burn up your pump.
 

Rusty123

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You probably have a check valve above ground. Remove that check valve and water hammer on pump start will go away.

Oh, and your sprinkler zones SHOULD be set to keep the pump running continuously. It is the cycling on and off that will burn up your pump.

I’m not aware of any above ground check valves (other than the BFP on the sprinkler branch), but I’ll give it another look.

With regards to the continuous pump running - I didn’t word that very well. My concern is with continuous pump running *with no flow*, such as would occur if a sprinkler zone valve malfunctioned.
 

Valveman

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A pump start relay actually causes the pump to run against a deadhead if the sprinkler valve fails to turn on the sprinklers. When using a pressure switch and tank, the pressure switch will shut off the pump if that happens. Either way a 75 PSI pressure relief valve is a good idea to prevent deadheading the pump. Sometimes even a pressure switch fails to turn off the pump, and the prv will pop off enough water to keep the pump cool.
 
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