Abstract: This paper introduces the working principle of self-operated differential pressure control valve and discusses the application of the valve in the protection of cold and heat source and the district heating project.
Key words: Self-operated differential pressure control valve, cold and heat source protection, central heating
0 Preface
The so-called self-operated pressure control valve, its function is to control the network of a branch or a user's pressure, so that the basic constant, and their own pressure drop is the change, it is through the adjustment Its own opening, to adjust their own consumption of pressure, in order to achieve the controlled object pressure is constant. This differential pressure control valve in the heating and air conditioning projects have been more applications, especially in household metering heating project has been widely used, so we are familiar with and understand. This article describes a different function with its own differential pressure control valve, its role is to control their own pressure, which can be called its own differential pressure control valve. At the same time, it discusses its application in HVAC project.
1, structure and working principle
Here to ZY47-16C own differential pressure control valve, for example, describes the working principle of their own differential pressure control valve. Figure 1 is the valve structure and working principle diagram. The spring, the pressure sensitive film and the stem are fixed together, and the outlet pressure P2 is introduced into the sealing cavity at the upper part of the pressure sensitive film through the pressure guiding tube. The lower part of the pressure sensitive film is the inlet pressure P1. The pre-compression amount of the spring is determined according to P1-P2 setting value ΔPs (hereinafter referred to as set pressure difference), even if the elastic force of the spring is equal to the force exerted by the pressure-sensitive film on the spring under the set pressure difference condition. And in accordance with the valve plug travel is much smaller than the principle of spring pre-compression select the spring. This makes the valve at any opening balance, the valve inlet and outlet pressure difference ΔP and set pressure difference ΔPs approximately equal. Strictly speaking, the opening degree is different, and the equilibrium state ΔP is not equal. Obviously, as the opening increases, the equilibrium state of the ΔP is increased. However, by selecting the spring, it is entirely possible to control the deviation of the balance ΔP from ΔPs within a certain range (for example, 10%) over the entire stroke of the valve plug.
Self-pressure differential valve in the work of the system can be divided into two situations: ① The current state is off. If the valve before and after the pressure difference ΔP is less than the set pressure difference ΔPs, then continue to shut down, then it is a shut-off valve. If ΔP is greater than ΔPs, the pressure-sensitive film overcomes the spring force and drives the valve plug to rise and the valve opens. When the equilibrium state is reached, the pressure difference ΔP between the inlet and outlet drops approximately to the set pressure difference ΔPs. ② The current status is on. If the system is stable, inlet and outlet pressure difference ΔP is approximately the set pressure difference. If ΔP increases due to changes in system conditions, the valve opens and the flow rate increases. At equilibrium, ΔP falls approximately to ΔPs. Valve is the maximum opening, there is ΔP greater than ΔPs, the valve no longer has the ability to regulate the pressure. If the system operating conditions change so that the inlet and outlet pressure difference ΔP is less than ΔPs, the valve is closed and the flow rate is reduced. When equilibrium is reached, ΔP rises to ΔPs again. Until the valve is closed, the occurrence of ΔP less than ΔPs, it no longer has the ability to regulate pressure, and become a shut-off valve. In short, self-pressure control valve in the closed state, ΔP must be greater than ΔPs to open; open state, the opening can be automatically adjusted to maintain the pressure before and after the valve is essentially constant.
2, its own pressure control valve in the HVAC project application
2.1 in the protection of cold and heat source applications
In recent years, in heating projects, fuel and gas units have more applications. Due to the implementation of metering and heating for heating, the user's awareness of flow regulation is greatly enhanced. In addition, the usage of hot water for domestic use varies a lot in a day, which makes the flow of the heating system greatly changed. If the flow is too small, it may cause partial boiling of the fuel and gas units, which in turn may damage the unit. For a chiller unit in an air conditioning system, if the chilled water flow rate is too small, it may also cause partial freezing of the evaporating piping, thereby damaging the unit. For the above two cases, as shown in Figure 2, in the bypass pipe, equipped with its own differential pressure control valve. Due to user adjustments and other reasons to reduce the system flow, differential pressure control valve before and after the pressure ΔP will increase, when ΔP is greater than the set pressure differential ΔPs, the pressure control valve opens to increase through the cold heat source Flow, to ensure the safe operation of the unit. When the differential pressure control valve is in the open state, the pressure difference around the valve can be kept constant. While the flow through the valve is the opposite of the flow of the user's system. That is, the flow of the user system is reduced and the flow rate through the pressure difference control valve is increased; on the contrary, the flow of the user system is increased, and the flow through the pressure difference control valve is reduced. This will ensure that the flow through the cold and heat sources will not have much change, both to protect the hot and cold sources, but also improve the stability of the unit operation.
The traditional way of protecting hot and cold sources is to install an electric differential pressure control valve on the bypass line. When the system flow decreases so that the differential pressure across the motorized valve is greater than the set pressure differential, the electric signal actuates the motorized valve to open, keeping the cold and heat source units at the minimum required flow rate. However, the electric differential pressure control valve due to the power and the transmission of electrical signals rely on the circuit, less reliable than self-operated pressure control valve. In addition, the price is higher than the latter. Therefore, in the protection of hot and cold sources, it is entirely possible to use their own pressure control valve to replace the traditional electric control valve. Incidentally, it is not appropriate to install a solenoid valve in the bypass line shown in FIG. 2 because the solenoid valve is closed and fully opened, so that each of its operations will generate a flow to the user's system Greater impact.
2.2 in the central heating system applications
It is often the case in district heating projects that heating users have low (low or low) and high (high or high) buildings, To meet the low-building radiator is not crushed requirements, high-rise buildings will be empty phenomenon; if the heat network pressure conditions to meet the high-rise buildings do not appear emptied, then the low-building radiator will exceed the pressure Its pressure capacity. With their own pressure control valve can often solve this conflict.
Figure 3 is an example of a terrain difference, the heat source is located in the lower case. According to the characteristics of the terrain, a pressurized water pump is installed in the appropriate position of the water supply pipeline, and a self-contained differential pressure control valve is installed at an appropriate position of the water return pipeline. During the system operation, the differential pressure before and after the pressure control valve can be maintained substantially constant. This will be divided into two parts hydrodynamic pressure line network, the front of the hydrostatic pressure line is relatively low, to meet the low-building radiator is not crushed requirements; hydrodynamic pressure at the rear of the relative High, to meet the high building does not happen emptying requirements. When the system is out of operation, the whole network of piezometric pipe head has reached a consistent trend, while the pressure control valve by reducing the opening to maintain the original pressure difference remains unchanged until the pressure control valve is closed. At this time, the differential pressure control valve and the check valve on the water supply line isolate the rear of the network from the front. The hydrostatic pressure line on the front of the network is guaranteed by the replenishing and pressurizing device installed on the heat source. The hydrostatic line at the back of the network is guaranteed by a constant pressure replenishment pump fitted with a differential pressure control valve.
1 Heat source 2 Circulating water pump 3 System feed water pump 4 Own differential pressure control valve 5 Pressurized water pump 6 Check valve 7 Network back-up feed water pump 8 Replenishment pressure control valve 9 Hot user
On the other hand, if there is a great difference in terrain and the heat source is at a high level, as shown in Figure 4, along the topographical features, a differential pressure control valve is installed at an appropriate position on the water supply pipe and a pressurized water pump . System operation, the differential pressure control valve before and after the pressure can be maintained substantially constant, so that the hydrodynamic pressure at the back of the network is relatively low line to meet the low-building radiator is not crushed requirements; before the network Department of hydrodynamic pressure line is relatively high, to meet the high building does not happen empty phenomenon. When the system is out of operation, the differential pressure control valve automatically closes and, together with the check valve on the return line, isolates the rear of the network from the front. The hydrostatic pressure line at the front of the network is ensured by the replenishing and pressurizing device set on the heat source. The hydrostatic pressure line at the back of the network is ensured by the replenishment regulating valve on the replenishment line connecting the front and the back.
1 heat source 2 circulating pump 3 system feed water pump 4 own differential pressure control valve 5 pressurized water pump 6 check valve 7 rear pressure control valve 8 hot water users
3, conclusion
Self-Own own differential pressure control valve is closed, if the valve before and after the pressure difference is less than the set pressure, then continue to close; if the valve before and after the pressure difference is greater than the set pressure, the valve opens. To open the state, it can automatically adjust the opening, the valve before and after the pressure drop is almost constant.
Self-pressure differential pressure control valve can be used for the protection of hot and cold sources, compared with the traditional electric control protection, reliable control, low cost advantages.
Self-pressure control valve itself can be used to solve the central heating project in the high-rise buildings and low building height difference caused by pressure on the working conditions require different contradictions.
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