Constant pressure device is fully automatic water booster pump system.It works as follows: When the artificial device to automatically start running,first detecting the presence of water, to ensure that the water pressure is less than the set pressure.If the pressure is less than the set then start accumulating the running time of a little water  pump for frequency water supply; when the water pressure is still less than the set pressure, and detection lasted more than two minutes, turn the power frequency , start the next pump in order to achieve a constant frequency operation pressure water supply (if more than two pumps, it is determined the cumulative running time). When the water use is reduced at this time (ie, the current state of operation, the water pressure is greater than the set pressure), the water pressure will be increased, then the variable-speed pump will reduce the frequency, when the frequency is below 20HZ  and lasted more than 5min, stop the first starting pump , ensure first start first stop, so that the use of two pumps cumulative time difference is small. When there is no water that water pressure is zero, the device automatically shut down to protect the pump and motor. When water consumption increases or a burst pipe that pumps   the phenomenon all started and longer than the set up requirements such as 30 min or less than the set pressure, self-alarming. After the power failure, when power on, the PLC will detect the voltage and the water pressure . If it is normal, no alarm signal   after each start the device according to the preset pressure to start constant pressure  water booster pump system.