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The differential pressure type flow switch is designed according to the curve of resistance and flow of HVAC equipment. We know that the heat exchanger, water filter, water pump and valve of HVAC equipment, they all have their performance curve of resistance and flow. By detecting the difference of inlet and outlet water pressure at both ends, and comparing with the preset value of the device, the flow can be accurately controlled.
Compared with the target type flow switch, the differential pressure flow switch is an accurate flow control mode, which has accurate flow control value. From the pressure difference switch, connecting two copper pipes to the inlet and outlet of the heat exchanger, measure the pressure difference between the inlet and outlet, that is, reflect the flow. The installation is very simple, which avoids the hidden trouble of unit failure caused by inaccurate installation of target water flow switch.
The differential pressure type flow switch has the characteristics of accurate flow control, no additional resistance to the system, no requirement for pipe diameter, and no disturbance of water flow. It can replace any type of target type flow switch as the flow control of HVAC water system. Compared with the target type flow switch, it can avoid the false flow caused by pump cavitation (the actual flow rate is large, but there is air mixed in the water And the actual flow is not large), and the field installation does not affect the flow control value of the differential pressure flow switch.
Differential pressure type flow switch can be widely used in large, medium and small air-cooled or water-cooled chillers with brazed plate heat exchanger, sleeve heat exchanger and shell and tube heat exchanger for water flow control and part of antifreeze protection. According to the very accurate characteristics of the flow control of the differential pressure type water flow switch, it can also expose the improper design or installation of the external water pipeline of the unit, and prompt the installation personnel to exclude the installation or change the pipeline design.
The differential pressure flow switch with proper action and reset value can be used as an important basis to check whether the design and installation of water system outside the chiller are correct. Because for a certain chiller, no matter what your installation situation is, the water flow through the heat exchanger does not reach the reset flow of the differential pressure switch (the test data in the factory configuration, the model of the differential pressure switch does not change and its reset flow does not change). The differential pressure switch will not close. When the field is not closed, there must be a problem in the water system outside the unit, and the reset flow is not reached.
Generally, the resistance of the system water pipeline is too large, some valves are not opened, the water pump is not vented, the filter is blocked, and the pipeline is not vented, etc., prompting the installation person to check and solve one by one, which has a guiding role. Because the installer usually does not have a flowmeter, it is impossible to test the flow of the installed water pipeline. If the target flow switch is used, it is difficult to determine the problem of the water pipeline, because the flow of the water pipeline cannot be determined.
The differential pressure type flow switch can effectively protect the water flow caused by the filter blockage from the flow protection value. If the two-way valve is used for the coil unit at the end of the installation unit, i.e. the variable water system is used incorrectly, when the number of two-way valves is gradually closed, once the flow of the two-way valve being opened is less than the off flow of the differential pressure switch, the differential pressure switch will accurately output the off signal within 3 seconds.
The water flow protection of evaporator is very important. Proper water flow protection value can avoid the possibility of freezing of evaporator due to the decrease of water flow of heat exchanger. Therefore, the water flow switch of the evaporator is often installed in the main engine by the main engine plant, and has been adjusted to the most appropriate protection set point, so as to avoid the hidden danger caused by the abnormal installation or setting of the water flow switch due to the level of the field installation personnel.
When selecting the type differential pressure switch, first is to determine the rated water flow of the unit, assuming that the refrigerating capacity of the unit is measured at the rated flow of the outlet water temperature of 7C and the return water temperature of 12C, assuming that the refrigerating capacity is unchanged, and the water flow is reduced to 50% of the rated flow, then the outlet water temperature may be as low as 2C, close to the freezing protection temperature, which is very dangerous, so we suggest the differential pressure water flow switch The set value of the flow action protection is greater than 50% of the rated flow. The set value of the flow protection can be roughly obtained from the curve of the pressure drop and flow of the heat exchanger, and then verified by the flow meter test.
Reset flow value means the water flow rate to close the differential pressure switch, when water flow through the heat exchanger by pump. Accurate reset flow is a key indicator to check whether the external water flow of the unit is normal. If the differential pressure switch cannot be back after the installation of the user, it often indicates that the external water system of the unit is 100% defective!!! No doubt!!! Prompt the user to check the design and installation of the external water system of the unit, because once the differential pressure type flow switch is installed on the heat exchanger in the air conditioning unit, any situation of the user's field installation will not affect the accuracy of its flow control, so it is convenient for the field installation personnel to find out the installation problem of the water pipeline of the unit. Reset flow is recommended to be less than 80% of rated flow.
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The protection flow rate refers to the sudden flow drop during the operation of the unit, which may be caused by the filter blockage, improper operation, closing the pipeline valve without shutdown and the wrong use of the water change system, i.e. the flow drop can be reflected within one second and this information can be provided to the host controller. Therefore, accurate reset and protection flow can completely avoid the heat exchanger freezing due to water flow.
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For the condenser, proper cooling water flow can ensure that the refrigeration system of the air conditioning host works in a better state, and ensure the working efficiency of the unit. When the water flow is too small, not only the condensation pressure increases, but also the refrigeration capacity decreases. In serious cases, the compressor may fail.
If the air conditioning unit does not get proper cooling water flow, the compressor will not work, which can fully protect the compressor from failure. Reset flow can detect whether the flow of water system meets the design requirements. Correct setting of pressure difference switch reset flow can ensure the water flow required to pass through the heat exchanger. Generally, the reset flow is 60-80% of the rated flow
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