Controlling Well Pump Cycling
by Damian Zawacki,
John Deere Landscapes Technical Training Manager

"My well pump is constantly cycling on and off. How can I alleviate this problem?" This is a question that troubles both turf managers and irrigation installers. To understand cycling, let's review a little background about deep well pumps. Deep well pumps are generally "submersible," which means they are installed underground (in the water table below) with all the pump controls located above grade where it is nice and dry.

Once installed, the pump is turned on and off by water pressure, which is controlled by a "pressure switch." If the water pressure is too low, the pump turns on. If the water pressure is too high, the pump turns off. This process of turning on and off is called cycling.

Unfortunately, cycling can be very destructive to a well pump because it shortens the life of the motor and puts excessive wear on the control components. Our goal is to minimize cycling as much as possible, while achieving optimal irrigation coverage.

"How can we control pump cycling"? We can control cycling with a couple of different methods.

Method #1

The least expensive solution (and easiest) is to adjust the pressure switch, which is located on the pump controls. Sometimes the pressure switch is set too high or too low for your particular application. Adjusting the "off" pressure (also known as the "cut-out pressure") is as simple as turning the adjustment screw. However, don't turn it too high, otherwise the pump may never shut off.

A second adjustment screw on the control panel is for the "differential." This is the difference (in PSI) between the on and off pressure setting. A standard setting is 20 PSI, but it can be increased for less cycling.

Adjusting these two pressure settings is a very simple process, but if you are not familiar with pump cycling, you may need to talk to the manufacturer or well driller before making these changes. Remember, adjusting of the pressure switch inaccurately may adversely affect the operation of the pump (which means the pump may never shut off).

Method #2

The pump may be cycling because the pressure tank is waterlogged. If the pump hardly ever cycled in the past, but now is a common occurrence, the pressure tank may no longer have air in it.

Pressure tanks act as a holding tank for water and air. There must be air pressure in the tank to help minimize cycling. When the pump is off, the air forces the water out of the tank. When the pump is running, it replenishes the water into the tank for the next cycle.The tank is usually charged with air pressure equal to or slightly less than the "turn-on pressure" (also known as the "cut-in pressure") of the pump. If the pump turn-on pressure is 40 PSI, then the tank air pressure should be 38 PSI.

When recharging a pressure tank with air, first completely drain out all the water. The tank must be completely void of water prior to recharging it with air. Once we recharge the tank with air, the gate valve to the tank can be opened to allow water refill the tank.

Method #3

There may not be enough demand for the pump. If we install an irrigation system that is in operation for several hours day, the pump should turn on and off only once - at the beginning and end of the irrigation program. If it cycles every five minutes, we are not operating enough sprinkler heads, thus not creating enough demand.

The sprinkler system might be demanding 10 GPM, but the pump needs to run 15 GPM to prevent it from reaching the off (high cut-out) pressure setting. Designing the sprinkler system to match the output of the pump is a necessity. There are two ways to determine the output of the well pump, prior to installing the sprinkler system.

First, review the pump performance specs from the well driller or pump manufacturer. This is the easy method, if it's a new well and we can contact the well driller.

Second, figure the output by creating a "test demand." By turning on several faucets, one at a time, you will get an idea how much water the pump is producing. Once you turn on enough faucets so that the pump runs continuously you will have the optimal performance point. You could turn on additional faucets, but once you start exceeding the optimal point; the pump will produce less pressure, creating inefficient performance.

For example, turn on three faucets and listen for the pump to cycle. If its cycling, turn on a forth faucet. If you have four faucets on and the pump stops cycling (which means its running continuously), then four faucets will be the optimal point. If you operate five faucets or more, the pump will start producing less pressure, and will adversely affect the irrigation system.

With four faucets operating, you can measure how much water is coming from each faucet, which determines the optimal performance point.

The best way to measure the faucet output is with a bucket and a stopwatch. Measure how much water you are getting from each faucet, then adds them all together. This will give you the optimum point in GPM or gallons per minute. If we design the irrigation system at the proper gallons per minute the pump will not cycle unnecessarily.

Method #4

Lastly, you can add a cycle stop valve to control cycling. This device automatically chokes back the output of the pump to match the output of the irrigation system. Essentially, the "constant speed" pump becomes a "variable speed" pump that will ramp up or down to match the sprinkler requirements. The cycle stop valve is installed at prior to the pressure tank and pressure switch. Essentially, the cycle stop valve has to be the first (or beginning) component on the system.