The oil pressure difference controller maintains a certain pressure difference in the area where the pressure difference needs to be established. For example, the discharge pressure of the compressor lubricating oil should be 0.1~0.2MPa higher than the pressure inside the crankcase in order for the compressor to operate normally. When the pressure difference reaches a certain level, the air pressure difference controller should proceed to the next program operation. For example, when the pressure difference between the inlet and outlet of a coiled air filter in an air conditioning system exceeds a certain value, it indicates that the filter material cannot continue to work and should be automatically replaced with a new material. At this time, the pressure difference controller can be used to automatically operate.
1.Types of pressure difference controllers
Pressure differential controllers are divided into mechanical and electronic pressure differential controllers based on their sensor structure.
The mechanical differential pressure controller is mainly divided into diaphragm type and spring type, and the deformation of the diaphragm or spring itself causes the actuation switch to act, causing the electrical signal to be output. Therefore, its accuracy is very low and unstable. Mainly used in some industrial places with low requirements for pressure difference accuracy. Common brands include Honeywell, Johnson, and Siemens.
The core of an electronic pressure difference controller is a pressure difference sensor. The pressure difference controller introduces pressure to the pressure difference sensor through two pressure detection ports, and its force acts on the wafer structure inside the pressure difference sensor, thereby changing the sensor capacitance. Then, electronic circuits are used to detect this change, and through an A/D converter (analog to digital), the relative stress, i.e. the pressure difference, is converted into a standard electronic signal, Then, the microprocessor outputs electrical signals based on logical settings.
Wafers have much higher structural stability than membranes or springs, so the accuracy of electronic differential pressure controllers is much higher than that of mechanical differential pressure controllers.
2. Working principle of pressure difference controller
The differential pressure controller is a protective device used to prevent damage to the bearing shells of refrigeration compressors due to insufficient lubricating oil pressure. If the oil pressure cannot be established within 60 seconds after the refrigeration compressor is started, the pressure difference controller will automatically cut off the power supply to ensure the safe operation of the system.
The working principle of the pressure difference controller is to act on two opposite pressure sensing elements (bellows). The force generated by the difference between two different pressures is balanced by the spring if it is less than the set value. Due to the action of the lever, the switch is turned on to the electric heater in the delay mechanism. Within a certain delay range (about 60 seconds), the delay switch is activated, and the motor power is cut off to stop the compressor. At the same time, the heater stops heating. The delay mechanism of the controller is equipped with a manual reset device. When the compressor stops due to the inability to establish oil pressure, the controller cannot automatically reset after action. It is necessary to press the reset button again after troubleshooting to connect the delay switch in the delay mechanism to the motor power supply and start the compressor.
The shell cover of the differential pressure controller is equipped with a test push button to test the reliability of the delay mechanism. When the refrigeration compressor is running, it will be pushed or pushed in the direction of the arrow, and the pushing time must be greater than the delay time. After a certain delay time, if the motor power can be cut off, it indicates that the delay mechanism can work normally.
