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| The principle of the bearing between the mechanical industry and the valve is different. |
| Time:2018-7-25 14:44:03 Views:1857 |
| The so-called self-operated differential pressure control valve has the function of controlling the pressure difference of a branch or a user in the network to make it substantially constant, and the pressure difference consumed by itself is changed. The opening degree of the self is adjusted to adjust the pressure difference consumed by itself to achieve a constant pressure difference of the controlled object. This type of differential pressure control valve has been widely used in heating and air conditioning projects, especially in the household metering heating project, so it is familiar and familiar. This paper introduces a self-operated differential pressure control valve with different functions. Its function is to control its own differential pressure, so it can be called its own differential pressure control valve. At the same time, explore its application in HVAC engineering. 1, structure and working principle Here, the ZY47-16C self-pressure differential control valve is taken as an example to introduce the working principle of the self-pressure differential control valve. Figure 1 is a schematic view of the structure and working principle of the valve. The spring, the pressure sensitive film and the valve stem are fixed together, and the outlet pressure P2 is introduced into the sealing cavity of the upper part of the pressure sensitive film through the pressure guiding tube, and the lower part of the pressure sensitive film is the inlet pressure P1. The pre-compression amount of the spring is determined according to the set value ΔPs of P1-P2 (hereinafter referred to as the set pressure difference), even if the spring force of the spring is equal to the force of the pressure-sensitive film against the spring under the set pressure difference condition. The spring is selected according to the principle that the stroke of the valve plug is much smaller than the pre-compression amount of the spring. This makes the inlet and outlet pressure difference ΔP of the valve approximately equal to the set pressure difference ΔPs in the equilibrium state of any opening of the valve. Strictly speaking, the degree of opening is different, and the ΔP of the equilibrium state is not equal. Obviously, as the opening degree increases, the ΔP of the equilibrium state increases. However, by selecting the spring, it is completely possible to control the deviation of the equilibrium state ΔP from ΔPs within a certain range (for example, 10%) within the entire stroke of the valve plug. The operation of the self-operated self-pressure differential control valve in the system can be divided into two cases: 1 The current state is closed. If the valve differential pressure ΔP is less than the set pressure difference ΔPs, it will continue to close, which is a shut-off valve. If ΔP is greater than ΔPs, the pressure sensitive film overcomes the spring force of the spring, drives the valve plug to rise, and the valve opens; when the equilibrium state is reached, the inlet and outlet pressure difference ΔP approximately falls back to the set pressure difference ΔPs. 2 The current status is on. If the system is running stably, the inlet and outlet pressure difference ΔP is approximately the set pressure difference. If ΔP is increased due to changes in system operating conditions, the valve opens and the flow rate increases; when the equilibrium state is reached, ΔP falls back to ΔPs. When the valve is at the maximum opening degree, the ΔP is greater than ΔPs, and the valve no longer has the ability to regulate the differential pressure. If the inlet and outlet pressure difference ΔP is less than ΔPs due to changes in system operating conditions, the valve is closed and the flow rate is reduced. When the equilibrium state is reached, ΔP rises to approximately ΔPs. When the valve is closed, ΔP is less than ΔPs, and there is no longer the ability to regulate the differential pressure, but become a shut-off valve. In short, when the self-operated self-pressure differential control valve is in the closed state, ΔP must be greater than ΔPs to open; in the open state, the opening can be automatically adjusted to keep the differential pressure before and after the valve substantially constant. 2. Application of self-pressure difference control valve in HVAC engineering 2.1 Application in protecting cold and heat sources In recent years, fuel and gas units have had more applications in heating projects. Due to the metering and charging of heating, the user's awareness of self-regulating flow is greatly enhanced, and the consumption of domestic hot water varies greatly within one day, so that the flow rate of the heating system has a large range of variation. If the flow rate is too small, it may cause partial boiling of the fuel and gas units, which may damage the unit. For the chiller in the air conditioning system, if the chilled water flow is too small, the evaporation pipe may be partially frozen, and the unit may be damaged. For the above two cases, as shown in Figure 2, a self-operated self-pressure differential control valve is installed on the bypass line. Due to user adjustment and other reasons, the system flow is reduced, and the differential pressure ΔP before and after the differential pressure control valve is increased. When ΔP is greater than the set differential pressure ΔPs, the differential pressure control valve is opened to increase the passage of the cold heat source. The flow ensures the safe operation of the unit. When the differential pressure control valve is open, the differential pressure before and after the valve can be kept substantially constant. The flow through the valve is inversely different from the flow of the user system. That is, the flow rate of the user system is reduced, and the flow rate of the control valve is increased by the differential pressure; otherwise, when the flow rate of the user system is increased, the flow rate of the control valve is decreased by the differential pressure. In this way, the flow rate through the cold heat source is not changed too much, which not only protects the cold heat source, but also improves the stability of the unit operation. The traditional way to protect the cold and heat source is to install an electric differential pressure control valve on the bypass line. When the system flow is reduced, so that the differential pressure before and after the electric valve is greater than the set pressure difference, the electric signal drives the electric valve to open, so that the cold heat source unit maintains the minimum flow required. However, the electric differential pressure control valve is less reliable than the self-operated differential pressure control valve due to its dependence on the power supply and the line that transmits the electrical signal. In addition, the price is much higher than the latter. Therefore, in terms of protecting the cold and heat source, it is completely possible to replace the conventional electric control valve with a self-operated self-pressure differential control valve. Incidentally, it is not appropriate to install a solenoid valve in the bypass line shown in Fig. 2, because the solenoid valve has only two states of being closed and fully open, so each action of the solenoid valve will generate flow to the user system. Larger impact. 2.2 Application in central heating systems In central heating projects, it is often the case that heating users have low buildings (lower buildings or lower-rise buildings) and high buildings (high-rise buildings or higher-rise buildings), if the pressure conditions of the heating network To meet the requirements of low-rise radiators that are not crushed, high-rise buildings will be emptied; if the pressure conditions of the heating network meet the high-rises without emptiness, the pressure of the low-rise radiators will exceed Its pressure capacity. This contradiction can often be solved by means of a self-pressure differential control valve. 3 is an example of a disparity in terrain and a low heat source. Following the characteristics of the terrain, a pressurized water pump is installed at an appropriate position of the water supply pipeline, and a self-operated self-pressure differential control valve is installed at an appropriate position of the return water pipeline. The differential pressure before and after the differential pressure control valve can be kept substantially constant during system operation. In this way, the hydraulic water pressure line of the network is divided into two parts, and the front hydraulic pressure line is relatively low, which can meet the requirement that the low-rise radiator is not crushed; the rear hydraulic pressure line is relatively relatively High, can meet the requirements of high buildings without emptiness. When the system stops running, the pressure pipe of the whole network has a consistent trend, and the differential pressure control valve tries to maintain the original pressure difference substantially by reducing the opening degree until the differential pressure control valve is closed. At this time, the differential pressure control valve, together with the check valve on the water supply line, isolates the rear of the network from the front. The hydrostatic line at the front of the network is guaranteed by a hydration constant pressure device located at the heat source. The hydrostatic line at the rear of the network is guaranteed by a constant pressure make-up pump fitted with a differential pressure control valve. 1 heat source 2 circulating water pump 3 system feed water pump 4 self-pressure differential control valve 5 pressurized water pump 6 check valve 7 network rear feed pump 8 hydration pressure regulating valve 9 hot user On the contrary, if the terrain is very different and the heat source is high, as shown in Figure 4, along with the characteristics of the terrain, a pressure differential control valve is installed at the appropriate position of the water supply pipeline, and a pressurized water pump is installed at the appropriate position of the return water pipeline. . When the system is running, the differential pressure before and after the differential pressure control valve can be kept substantially constant, so that the dynamic water pressure line at the rear of the network is relatively low, which can meet the requirement that the low-rise radiator is not crushed; The dynamic water pressure line of the Ministry is relatively high, which can satisfy the phenomenon that high buildings do not empty. When the system stops running, the differential pressure control valve automatically closes, and together with the check valve on the return pipe, isolates the rear of the network from the front. The hydrostatic pressure line at the front of the network is ensured by the water supply and pressure constant device installed in the heat source. The hydrostatic pressure line at the rear of the network is ensured by the water supply regulating valve on the water supply pipe connecting the front and the rear. 1 heat source 2 circulating water pump 3 system feed water pump 4 self-pressure differential control valve 5 pressurized water pump 6 check valve 7 rear water pressure regulating valve 8 hot user 3. Conclusion When the self-operating self-pressure differential control valve is in the closed state, if the pressure difference between the front and the rear of the valve is less than the set pressure difference, the valve is continuously closed; if the pressure difference between the front and the rear of the valve is greater than the set pressure difference, the valve is opened. When it is in the open state, the opening degree can be automatically adjusted so that the pressure difference between the front and the rear of the valve is substantially constant. The self-operated self-pressure differential control valve can be used to protect the cold and heat source, and has the advantages of reliable control and low price compared with the traditional electric control protection. The self-operated self-pressure differential control valve can be used to solve the contradiction between different requirements for pressure working conditions caused by the great difference between the high building and the low building height in the central heating project. |
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