A pressure relay is an element in a hydraulic system that activates electrical contacts when the fluid pressure reaches a predetermined value. A pressure relay can also be defined as a hydraulic component that converts pressure into an electrical signal. The customer can adjust the pressure relay according to his own pressure design needs to achieve the function of outputting an electrical signal at a certain set pressure.
Pressure relays are circuit switches controlled by electrical signals. When the discharge pressure of the compressor exceeds the set value or the suction pressure is lower than the set value, it can cut off the circuit and protect the safe operation of the refrigerator. In small refrigeration devices, pressure relays with high and low pressure are generally used, and FP type pressure relays are common (see Figure 159). It is composed of high and low pressure bellows, balance spring, lever mechanism, amplitude adjustment mechanism and electrical contacts. When the pressure changes, the bellows expands and contracts, and the electrical contact is pushed through the lever mechanism to cut or connect the circuit. The function of the low-pressure control element is to control the evaporation pressure of the refrigerant not to be too low to avoid the refrigerator working at unnecessary low temperatures and wasting electric energy.
The low-pressure capillary 1 on the pressure relay is connected to the suction pipe of the compressor i. When the evaporation pressure is lower than the set value, the low-pressure bellows 2 expands due to the action of the spring 3, so that the low-pressure thimble 4 retracts into the bellows ; The low-pressure lever 5 rotates in the direction of the hour hand due to the action of the spring 6. When the contact plate 7 connected to the lever moves upward, the contact 19 is tripped, and the circuit is cut off. The compressor stops working; when the pressure in the evaporator gradually rises to the two fixed value, i; the low-pressure bellows is compressed; The thimble extends from the bellows, rotates the entire lever in a clockwise direction, and causes the contact plate to drop onto the contact 19, connect the circuit, and the compressor restarts.
The function of the high-pressure control element is the same as that of the low-pressure, except that the condensing pressure is controlled not to be too high to avoid accidents. The high-pressure connection 9 is connected to the compressor exhaust pipe. When the exhaust pressure is higher than the set value, the high-pressure bellows 10 is compressed, the high-pressure thimble 12 pushes the lever 13 to move, the high-pressure circuit breaker 14 is turned up, the contact plate is pushed up, the circuit is cut off, and the compressor stops working. As the refrigerant vapor is continuously condensed in the condenser, the exhaust pressure continues to fall. When it drops to a certain value, the high-pressure thimble and the lever move in the opposite direction, so that the contact plate and the contact are connected, and the compressor resumes operation. .
Adjustment method of pressure relay:
(1) Adjustment of low pressure. Adjust the low-pressure adjustment screw T according to the pressure value corresponding to the required evaporation temperature: when a higher evaporation temperature is required, use a screwdriver to turn the low-pressure adjustment screw T counterclockwise; if a lower evaporation temperature is required, adjust it clockwise Screw T.
(2) Adjustment of high pressure. In order to ensure the safety of the operation of the refrigeration device, most of the pressure relays in the refrigerators with sub-water-cooled condensers are mainly used to prevent the cooling water from being interrupted, or the condensing pressure caused by the cooling water flow rate is suddenly increased rapidly, resulting in serious accidents . The high pressure value is generally set at 1Q ~ 11 kg/cm z-meter r-turn, 31 (with Freon 12 refrigerant). When adjusting, use a screwdriver to turn the high-pressure adjustment screw M clockwise, the pressure value increases, and counterclockwise rotation will decrease the pressure value.
Notes on the use of pressure relay
(1) According to the specific use and the pressure of the system, select a pressure relay with an appropriate structure. In order to ensure the sensitive operation of the pressure relay, avoid using a high-pressure pressure relay in the low-pressure system.
(2) The pressure relay should be installed correctly in accordance with the requirements of the manufacturer.
(3) Wire the micro switch in the pressure relay according to the required power supply form and specific requirements.
(4) After adjusting the pressure relay, its position should be locked or fixed. To avoid changes after vibration.
(5) The oil drain cavity of the pressure relay should be directly connected to the oil tank, otherwise the back pressure of the oil drain will be too high, affecting its sensitivity.