What are the specific applications of differential pressure control valves? Zhongda Consulting will answer them below.
The function of the commonly referred to self-operated pressure difference control valve is to control the pressure difference of a certain branch or user in the network so that it is basically constant, and the pressure difference consumed by itself is What changes is that it adjusts the pressure difference consumed by itself by adjusting its own opening, so as to achieve a constant pressure difference of the controlled object. This kind of pressure difference control valve has been widely used in heating and air conditioning projects, especially in household metering and heating projects, so it is familiar and understood by everyone. This article introduces a self-operated pressure difference control valve with different functions. Its function is to control its own pressure difference, so it can be called its own pressure difference control valve. At the same time, its application in thermal engineering is discussed.
1. Structure and working principle
Here we take the ZY47-16C self-differential pressure control valve as an example to introduce the working principle of the self-differential pressure control valve. Figure 1 is a schematic diagram of the structure and working principle of the valve. The spring, pressure-sensitive diaphragm and valve stem are bonded together, and the outlet pressure P2 is guided into the sealing chamber on the upper part of the pressure-sensitive diaphragm through the pressure guide tube. The lower part of the pressure-sensitive diaphragm is the inlet pressure P1. According to the set value ΔPs of P1-P2 ( (hereinafter referred to as the set pressure difference) determines the pre-compression amount of the spring, even if the elastic force of the spring is equal to the force of the pressure-sensitive film on the spring under the set pressure difference condition. And select the spring according to the principle that the stroke of the valve plug is much smaller than the pre-compression amount of the spring. In this way, in the equilibrium state of any opening of the valve, the inlet and outlet pressure difference ΔP of the valve is approximately equal to the set pressure difference ΔPs. Strictly speaking, if the opening is different, the ΔP of the equilibrium state is not equal. Obviously, as the opening increases, the ΔP of the equilibrium state increases. However, through the selection of the spring, it is possible to control the deviation of the equilibrium state ΔP relative to ΔPs within a certain range (such as 10%) within the full stroke of the valve plug.
The work of the self-operated self-pressure difference control valve in the system can be divided into two situations for explanation: ① The current state is closed. If the pressure difference ΔP between the front and rear of the valve is less than the set pressure difference ΔPs, it will continue to close, and it is a shut-off valve. If ΔP is greater than ΔPs, the pressure-sensitive membrane overcomes the elastic 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 open. If the system operates stably, the inlet and outlet pressure difference ΔP is approximately the set pressure difference. If ΔP increases due to changes in system operating conditions, the valve will open wider and the flow rate will increase; when reaching equilibrium, ΔP will approximately fall back to ΔPs. When the valve is at its maximum opening, ΔP will be greater than ΔPs, and the valve will not It also has the ability to regulate the pressure difference. If the inlet and outlet pressure difference ΔP is less than ΔPs due to changes in system operating conditions, the valve will be closed and the flow rate will decrease. When the equilibrium state is reached, ΔP will approximately rise to ΔPs. Until the valve is closed, ΔP will be less than ΔPs. , it no longer has the ability to regulate the pressure difference and becomes a shut-off valve. In short, when the self-operated self-operated pressure difference control valve is in the closed state, ΔP must be greater than ΔPs before it can be opened; when in the open state, the opening can be automatically adjusted to keep the pressure difference between the front and rear of the valve basically constant.
2. Application of self-pressure difference control valve in heat circulation engineering
2.1 Application in protecting cold and heat sources
In recent years, in heating In engineering, oil and gas units have many applications. Due to the implementation of metering and charging for heating, users' awareness of independently adjusting the flow rate has been greatly enhanced. In addition, the consumption of domestic hot water changes greatly within a day, resulting in a large range of changes in the flow rate of the heating system. If the flow rate is too small, it may cause local boiling of the fuel and gas unit, which may cause damage to the unit. For the chiller in the air conditioning system, if the chilled water flow is too small, it may also cause the evaporation pipe to freeze partially, thereby damaging the unit. For the above two situations, as shown in Figure 2, a self-operated self-pressure control valve can be installed on the bypass pipeline. Due to user adjustment and other reasons, the system flow rate decreases, and the pressure difference ΔP before and after the pressure difference control valve will increase accordingly. When ΔP is greater than the set pressure difference ΔPs, the pressure difference control valve opens, increasing the flow through the cold and heat source. flow to ensure the safe operation of the unit.
When the pressure difference control valve is in the open state, the pressure difference before and after the valve can always be kept basically constant. The flow rate through the valve changes inversely with the flow rate of the user system. That is, if the flow rate of the user system decreases, the flow rate through the differential pressure control valve will increase; conversely, if the flow rate of the user system increases, the flow rate through the differential pressure control valve will decrease.
This ensures that the flow rate through the cold and hot sources does not change too much, which not only protects the cold and hot sources, but also improves the stability of the unit's operation.
The traditional way to protect hot and cold sources is to install an electric differential pressure control valve on the bypass line. When the system flow decreases and the pressure difference between the front and rear of the electric valve is greater than the set pressure difference, the electric signal drives the electric valve to open to maintain the necessary minimum flow of the cold and heat source unit. However, the electric differential pressure control valve is not as reliable as the self-operated differential pressure control valve due to its reliance on power supply and lines for transmitting electrical signals. In addition, the price is also much higher than the latter. Therefore, in terms of protecting the cold and heat sources, it is completely possible to replace the traditional electric control valve with a self-operated self-pressure differential control valve. By the way, it is inappropriate to install a solenoid valve on the bypass pipeline shown in Figure 2. Since the solenoid valve only has two states: closed and fully open, every time it moves, it will affect the flow of the user system. greater impact.
2.2 Application in central heating systems
In central heating projects, it often happens that heating users have low buildings (shorter buildings or low-lying buildings). buildings) and high buildings (high-rise buildings or buildings on higher ground), if the pressure conditions of the heating network meet the requirements that the radiators of low buildings are not crushed, emptying will occur in tall buildings; if the heating network If the pressure conditions are such that tall buildings do not empty out, the pressure on the radiators of low buildings will exceed their pressure-bearing capacity. This contradiction can often be solved with the help of its own pressure difference control valve.
Following the terrain characteristics, a pressurized water pump is installed at an appropriate location in the water supply pipeline, and a self-operated self-pressure difference control valve is installed at an appropriate location in the return water pipeline. During the operation of the system, the pressure difference before and after the pressure difference control valve can remain basically constant. In this way, the dynamic water pressure line of the network is divided into two parts. The dynamic water pressure line in the front part is relatively low, which can meet the requirements of the radiator in low buildings not to be crushed; the dynamic water pressure line in the rear part is relatively low. High, which can meet the requirements of high-rise buildings without emptying. When the system stops running, the water heads of the pressure measuring pipes in the entire network tend to reach a consistent trend, while the pressure difference control valve tries to maintain the original pressure difference basically unchanged by reducing the opening until the pressure difference control valve is closed. At this time, the pressure difference control valve and the check valve on the water supply pipeline work together to isolate the rear part of the network from the front part. The hydrostatic pressure line at the front of the network is guaranteed by a water replenishing and constant pressure device set at the heat source. The hydrostatic pressure line at the rear of the network is guaranteed by a constant-pressure water supply pump equipped with a pressure difference control valve.
1 Heat source 2 Circulating water pump 3 System supply water pump 4 Self-pressure difference control valve 5 Pressurized water pump 6 Check valve 7 Network rear supply water pump 8 Supply water pressure regulating valve 9 Heat user
< p> On the contrary, if the terrain is very different and the heat source is at a high place, as shown in Figure 4, follow the terrain characteristics and install its own pressure difference control valve at the appropriate position of the water supply pipeline, and install a pressure control valve at the appropriate position of the return water pipeline. Pressure water pump. When the system is running, the pressure difference before and after the pressure difference control valve can be kept basically constant, so that the dynamic water pressure line at the rear of the network is relatively low, which can meet the requirements of the radiator in low buildings not to be crushed; in front of the network The dynamic water pressure line at the bottom is relatively high, which can prevent emptying of tall buildings. When the system stops running, the pressure difference control valve automatically closes, and together with the check valve on the return pipeline, isolates the rear part of the network from the front part. The hydrostatic pressure line at the front of the network is guaranteed by a water replenishment constant pressure device set on the heat source, and the hydrostatic pressure line at the rear of the network is guaranteed by a water replenishment regulating valve on the water replenishment pipeline connecting the front and rear.1 Heat source 2 Circulating water pump 3 System supply water pump 4 Self-pressure difference control valve 5 Pressurized water pump 6 Check valve 7 Rear water supply pressure regulating valve 8 Heat user
3. Conclusion
When the self-operated self-operated pressure difference control valve is in a closed state, if the pressure difference between the front and back of the valve is less than the set pressure difference, it will continue to be closed; if the pressure difference between the front and back of the valve is greater than the set pressure difference , the valve opens. When it is in the open state, the opening can be automatically adjusted to keep the pressure difference between the front and back of the valve basically constant.
The self-operated self-pressure differential control valve can be used to protect hot and cold sources. Compared with traditional electric control protection, it has the advantages of reliable control and low price.
The self-operated self-operated differential pressure control valve can be used to solve the contradiction in the different pressure working conditions caused by the huge difference in height between tall buildings and low buildings in central heating projects.
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