A low pressure cut-off switch is used to shut a pump off if you have a big leak, or if the well is pumped dry. But there are times when a low pressure cut-off switch cannot detect and protect the pump against dry well conditions. This occurs when the well pumps dry just about the same time as the people in the house shut off the faucets. While refilling the pressure tank, the pump loses prime and is unable to pump the pressure tank up to the cut-off pressure. And because there are no faucets open, the pressure tank does not drain down to the really low pressure setting that shuts off the pump for safety. So unless someone accidentally opens a faucet in the house within a few minutes, the pump, pipe, motor, and everything else gets hot very quickly. Getting away with this more than a couple of times without burning up the pump is just luck.
In really deep wells, or when using a Dole valve, the pump is restricted to very low flow (almost deadhead). With some pumps there is very little difference in the amp draw between deadhead and dry well condition. The pumptec and Cycle Sensor both look for low amps to determine a dry well condition.
Once the pumptec calibration button is pressed, the pumptec takes a snapshot. This determines the low amps for a dry well, by setting the low amp trip point 25% below the snapshot. When the amps are already low from a deep well or a Dole valve restrictor at “snapshot” time, the amps will not drop an extra 25% when the well is completely dry. I am not even sure what the “sensitivity” button on the newer versions of the pumptec is for. I think it reduces the 25% to a lower amount. You maybe able to make a pumptec “sensitive” enough, if you adjust this setting until the pump shuts off, after you are sure the well is pumped dry. I was told even the older models have a sensitivity dial. You just have to open the case to get to it. But I am not certain of this. Either way it seems like a trial and error type of setting.
The Cycle Sensor has a digital display that shows the amps in real time. You can actually see the amps at which the well is pumping water and compare to the amps when the well is pumped dry. The actual low amp trip setting needs to be between these two numbers. The Cycle Sensor can be set in 1/10th of an amp increments. So for instance it can be set to detect a dry well at 4.8 amps, even when the pump produces water at 4.9 amps and only drops to 4.7 when the well is dry.