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Working principle and application of plate heat exchangers. I. Working Principle of Heat Exchanger Units The JB series of high-temperature steam-water stainless steel plate heat exchanger units are composed of a temperature and pressure reduction device, plate heat exchangers, temperature control valves, circulation pumps (on the secondary side), make-up water pumps (optional), valves, instruments, an electrical control cabinet, and various accessories – forming what is essentially a complete \"heat exchange station\". The primary-side heat medium passes through the temperature control valve, enters the plate heat exchanger to release heat, and then is discharged ； The low-temperature water on the secondary side enters the plate heat exchanger via a circulation pump, is heated there, and then sent out. The temperature sensor is located at the hot water outlet on the secondary side, and it sends temperature signals back to the temperature control valve, which in turn adjusts the flow rate of the heating medium in order to control the temperature of the water exiting the secondary side. When setting up the make-up water pump, it receives pressure signals from pressure sensors and starts or stops automatically to maintain stable system pressure. To enhance the equipment’s adaptability in terms of regulation, the JB series plate heat exchanger units are equipped with a unique secondary side bypass circuit. This design helps to minimize the flow resistance loss in the secondary side, thereby allowing the use of circulation pumps that consume less electricity and helping to save energy. II. Before using the heat exchange unit’s system, fill it with water, supply power and the heating medium. Make sure to remove all air from the pipelines in the entire system, and ensure that all valves are functioning properly and keep the pathways unobstructed. Turn off the heat supply at each heating point (for example, turn off the motor of the fan coil unit, but do not close the inlet and outlet valves of the fan coil unit). 1. Close all valves for the heat medium on the primary side of the unit (regardless of whether the temperature control valves are open or closed), and open the valves on the secondary side ； 2. Close the valves at the interface of the secondary-side plate heat exchanger (if any), and fully open the secondary-side bypass valve ； 3. For the water pump control buttons in the electric control cabinet, check whether the rotation direction of each water pump motor matches the indicated arrow, and confirm that the water pumps are operating properly ； 4. Start the secondary side circulation pump and run it for a certain period of time to remove impurities from the pipes and discharge air ； 5. Adjust the opening degree of the secondary side bypass valve to ensure that the pressure difference between the inlet and outlet of the plate heat exchanger meets the specified requirements; once the adjustment is appropriate, fix the opening position of this valve and record it ； 6. Open the bypass valve on the condensate water pipeline at the primary side outlet once, then gradually open the bypass valve on the steam pipeline at the primary side inlet ； When the heat medium is high-temperature hot water, fully open the primary side outlet valve, and gradually open the bypass valve on the primary side inlet pipeline ； Be careful to observe the changes in the water temperature on the secondary side of the unit as well as other operational conditions while opening the inlet valve; in case of any anomaly, immediately close the inlet valve for the heat medium on the primary side first! Once the system is operating normally, fully open the valves before and after the steam trap on the condensate outlet line on the primary side, and slowly close the bypass valve; condensate should be discharged, with no significant amount of steam mixed in. When the heat medium is high-temperature hot water, fully open the primary side outlet valve, and gradually open the bypass valve on the primary side inlet pipeline ； Be careful to observe the changes in the water temperature on the secondary side of the unit as well as other operational conditions while opening the inlet valve; in case of any abnormalities, immediately close the inlet valve for the heat medium on the primary side first! 7. Set the control temperature of the water temperature automatic controller, and check whether the opening/closing position of the electric valve matches the actual requirements ； 8. Close the bypass valve on the primary side inlet pipeline, fully open the valve downstream of the electric valve, and gradually open the valve upstream of the electric valve. Observe the operation of the temperature control valve as well as the changes in the water temperature on the secondary side of the unit. It should be observed that the electric valve continuously adjusts up and down, with the amplitude becoming smaller and smaller until it stabilizes. The temperature controller will show fluctuations in the outlet water temperature on the secondary side, until it stabilizes within the specified tolerance range. 9. When shutting down the system, close the valves located before and after the electric valve at the primary side inlet, and then stop the secondary side circulation pump. Follow the above steps again when restarting. Once the unit has operated continuously for 24 hours without any issues, it can be put into normal operation. In the process of debugging and operation, if any unexpected situation occurs, the power supply must be cut off immediately, and the inlet valve for the heat medium on the primary side should also be closed! In addition to regular use, we also need to carry out periodic maintenance to ensure its proper operation and extended service life. In regular use, it is necessary to regularly check whether the unit is operating properly, as well as whether temperature and pressure control are functioning correctly; furthermore, the operating parameters of the unit should be recorded frequently. Especially during periods of shutdown when it is particularly cold in winter, it is necessary to shut off the inlet and outlet of the unit and drain the water from its pipelines to prevent freezing and cracking. Additionally, pay attention to maintaining and cleaning the unit, especially the temperature control valves, water pumps, and electrical control cabinets, to keep them clean and dry. After the unit has been in operation for some time, if issues such as insufficient heat exchange or a significant increase in the pressure difference between the inlet and outlet of the plate heat exchanger occur, it is advisable to consider cleaning the plate heat exchanger. In case of any faults, please contact the manufacturer for proper guidance.