Cycle Sensor: General Information
The Cycle Sensor is a system monitor that detects Rapid Cycle and Dry Run and reacts to either of
these conditions by shutting down the pump. It does not control or prevent rapid cycle or dry run
but protects your pump in the event these problems occur. This sensor was designed for a pump
that is controlled with a Pump Control Valve such as a Cycle Stop valve and/or is installed with
enough pressure tanks to prevent a rapid cycle condition. The pump must also be supplied with
enough fluid to prevent dry run which causes the undercurrent condition.
These units continuously display the load characteristics of the motor when it is running. When a
fault is detected, the relay will shut off power to the pump and display RCYCL for Rapid Cycle or
DRY for a Low Current condition. The unit can be reset by pressing the manual reset button or by
shutting off power to the unit and then powering back on.
The "Rapid Cycle" feature of this relay monitors the duration of time the pump is on. If the pump
"run time" is shorter than the Cycle Sensor minimum set time, the pump will be shut down before
damage from cycling occurs. Length of acceptable minimum pump run time is adjustable and can be
set for as little as 0 seconds to as much as 600 seconds. (Rapid cycling can be caused by water
logged or improperly sized tanks, improper pressure switch settings, control malfunctions, broken
check valves, and chattering contacts.)
This "Rapid Cycle" feature only allows for a manual reset. This means that when a rapid cycle is
detected, the pump is turned off and it will remain off until the Cycle Sensor is manually reset.
Undetected "short cycling" can lead to multiple problems such as submersible pumps unscrewing
themselves from the drop pipe and falling into the well, water hammer, contact failure, stripped
splines or couplings, broken pump or motor shafts, and ultimately system failure.
The "Dry Run" feature of the Cycle Sensor, unlike other similar relays that look for dry run
conditions, can detect the minute differences between the low current achieved when the pump is
restricted by a Cycle Stop Valve (or any other valve that restricts the pump to match a low flow
demand), and the slightly lower current that occurs when the pump has actually run dry. (For
example, if the inlet to the pump became clogged with debris and low current is not detected at
this point, the pump and or motor could be destroyed from a lack of cooling flow. Low current can
also be caused by cavitation and broken pump shafts or couplings). After a 10 second delay, the
pump will be shut down before damage from running dry can occur.
This "Dry Run" feature allows for either a manual reset or a timed restart. The timed restart is
adjustable from 0 minute to 300 minutes to allow low producing wells to recover before the pump
automatically restarts. The manual reset option is designed to protect systems where the loss of
the water supply would be out of the ordinary but a possibility.
Note: Standard overloads do not detect dry run or rapid cycle conditions until damage has
occurred and some part of the electrical system has failed. The Cycle Sensor does not control or
monitor overload conditions nor is it meant to replace standard overloads, which normally come in
the motor or motor starter.
The Cycle Sensor is available in three models:
Model CS1PH1-2HP works with 230V single phase pumps from 1/3HP to 2HP,
Model CS1PH3-15HP works with single phase pumps from 3HP to 15HP, and
Model CS3PH1-500HP works with three phase pumps from 1HP to 500HP.