A constant pressure system involves 4 main components:
1: Controller
The Controller can run off of either single phase or three phase power and comes in a variety of voltages. This provides power to the pump motor and speeds it up or slows it down according to the demand.  In order for the controller to be able to do this, it takes the incoming a/c (alternating) voltage and changes it to a dc voltage (similar to a battery).  After it does this it is able to rebuild the voltage that powers the motor into differing magnitudes in relation to the work that needs to be done.
2: Pressure Sensor
The pressure sensor sends a signal to the controller that is related to the pressure in the water line. The controller will take this information and will speed up or slow down the pump.
3: Three phase motor
This system uses a three phase motor. This type of motor allows for greater speed control and better performance at lower speeds compared to a single phase motor.
4: Pressure Tank:
The pressure tanks used in a constant pressure system are very small compared to a conventional system. These tanks should be at least 10% of the pumps maximum flow rate in gpm.
   For example a pump that could do 25 gpm (gallons/minute) 25x.10=2.5 gallon tank.
   A Standard system at the same flow rate would require at least a 50 gallon tank to
   give the pump a 2 minute reserve to prevent unwanted cycling.
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