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Three-Way Control Valve Construction and Performance
A three-way control valve is a type of multi-port control valve. According to the action mode of the fluid, the three-way valve can be divided into two types: converging valve and diverting valve. The confluence valve has two populations and flows out from one outlet after confluence. The diverter valve has a fluid port, which is divided into two streams and flows out from two outlets. The structure of the confluence three-way valve is similar to that of the split three-way valve. The three-way control valve is divided into electric three-way control valve and pneumatic three-way control valve according to the different drive actuator mechanisms. The characteristics of the three-way valve are as follows.
1. The three-way valve has two spools and seats, and its structure is similar to that of a double seat valve. However, in a three-way valve, when the flow area between one valve core and the valve seat increases, the flow area between the other valve core and the valve seat decreases. In a double-seat valve, the flow area between the two valve cores and the valve seat increases or decreases at the same time.
2. The air opening and closing of the three-way valve can only be achieved by selecting the positive and negative effects of the actuator. The change of the air opening and closing of the double seat valve can be realized by directly installing the valve body or valve core and the valve seat.
3. When the three-way valve is used in a control system that requires fluid to be proportioned, because it replaces an air-open control valve and an air-close control valve, it can reduce costs and reduce installation space.
4. The three-way valve is also used in places where the bypass is controlled. For example, one fluid passes through the heat exchanger to exchange heat, and the other fluid does not exchange heat. When the three-way valve is installed in front of the heat exchanger, use the split three-way valve; when the three-way valve is installed behind the heat exchanger, use the converging three-way valve. Because the fluid flowing through the three-way valve installed in front of the heat exchanger has the same temperature, the leakage is small; the fluid flowing through the three-way valve installed after the heat exchanger has different temperatures, which is very important for the valve core. The degree of expansion is different from that of the valve seat, so the leakage is larger. Generally, the temperature difference between the two fluids should not exceed 150C.
5. The leakage of the three-way control valve has a great relationship with the structure, and the leakage level can be from II to IV.
The three-way valve shown in the figure adopts a cage structure with a balance hole and is guided by the cage. Therefore, the unbalanced force can be greatly reduced. Early three-way valves used cylindrical thin-walled windows and were guided by the side of the valve core. Although it could reduce the unbalanced force, there was still a large unbalanced force when a stream of fluid was close to closing (flow direction). , With the change of valve opening, the unbalanced force changes. The cage structure with balance holes as shown in the figure can eliminate the unbalanced force and has a damping effect, which is conducive to the stable operation of the control valve. The three-way valve guided by the stem has a large balance force, and the required driving thrust is related to the fluid outlet, population pressure, friction, and pressing force.
Due to the large leakage of the three-way valve, two control valves (and the three-way connector) can be used to split or merge fluids, or to control the proportion of fluids in applications that require small leakage.
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