The three-way control valve is widely used to control the process parameters of gases, liquids, steam, and other media. Such as pressure, flow, temperature, levels, and other parameters are maintained at a given value. The three-way control valve is suitable for dividing a fluid into two outflows through the three-way valve. It can also combine two juices into one fluid working condition through the three-way valve.
The three-way control valve has a compact structure, lightweight, sensitive action, and accurate flow characteristics. It can directly accept the control signal from the input of the regulating instrument (4-20mA DC, 0-10mA DC, or 1-5V DC, etc.). Its single-phase power supply can control the operation. It can also achieve automatic regulation and control of the process pipeline fluid medium.
1. Structure of the three-way control valve
The 3-way control valve has three inlets and outlets connected to the pipeline. It is equivalent to two single-seat valves in one. We have divided the valves into three-way combined valves and three-way diverting valves.
1.1 Three-way combined valves
A three-way combined flow control valve is through which two fluids are mixed. For example, two liquids of different temperatures are mixed through the valve body with a juice of a temperature in between the first two.
1.2 Three-way diverter valves
A three-way diverter valve is one fluid that passes through the valve and then splits into two. When the valve closes one outlet, it’ll open the other outlet. This type of valve has one inlet and two outlets.
1.3 Difference in spool position between combined flow control valves and diverter control valves
The combined flow and diverter control valve spools are not in the same position. The spool of an integrated flow control valve is located within the two valve seats. The spool of a diverter valve is located outside the two seats. The design of the spool allows the flow direction to keep the spool in the open position.
The combined flow control valve provides a stable operation. Therefore, combined flow control valves are used in integrated flow applications. Diverter valves are used in applications where the flow is divided.
2. Characteristics of the three-way control valve
A combined flow three-way valve structure is similar to a split-flow 3-way valve. However, the three-way control valve differs according to the driving actuator mechanism it is fitted for. It is divided into electric three-way adjustment valves and pneumatic three-way adjustment valves. The characteristics of the three-way valves are as follows.
2.1 Structural features
The three-way valve has two spools and seats. Its construction is similar to that of a two-seat valve. However, in a three-way valve, the flow area between one spool and the seat increases while the flow area between the other spool and the seat decreases. In a double-seated valve, the flow area between the two spools and the center is increased or reduced simultaneously.
2.2 The role of the actuator on the three-way valve
Air opening and closing of three-way valves can be achieved by selecting the positive and negative actions of the actuator. The change of air opening and closing of a double-seated valve can be achieved by directly reversing the valve body or spool to the valve seat.
2.3 Fluid proportioning
The three-way valve requires a control system in which the fluid is proportioned. It replaces an air opening control valve and an air closing control valve. Therefore, it reduces costs. It can also reduce installation space.
2.4 Installation of heat exchangers
Three-way valves are also used where bypass control is required. For example, one fluid passes through the heat exchanger without the other fluid being exchanged.
When the 3-way valve is installed in front of the heat exchanger, we should use a split 3-way valve. When the 3-way valve is installed after the heat exchanger, we should use a combined flow 3-way valve. As a result, the fluid flowing through the 3-way valve installed in front of the heat exchanger has the same temperature.
Therefore, there is less leakage, and the fluid flows through the 3-way valve installed after the heat exchanger has a different temperature. As a result, it expands differently on the spool and seat. Therefore, fluid leakage is more significant. So the temperature difference between the two fluids should not exceed 150C.
The leakage of three-way control valves is highly dependent on the construction. Therefore, leakage classes can range from II to IV.
When the leakage is small, we can use two control valves (and a three-way receiver) for diverting or merging fluids or proportional control.
3. The guiding role of the three-way valve
To reduce unbalanced forces, we can use spool side guides. It is how early three-way valves used cylindrical, thin-walled windows. When a fluid is close to closing (flow off direction), there is still a large unbalance force. Moreover, the unbalance force varies with the valve opening and the unbalance force.
Then, the cage structure with balancing holes allows the unbalance force to be eliminated. When we use a stem-guided 3-way valve, it also has a damping effect. It facilitates the stable operation of the regulating valve. When the balancing force is large, the required driving thrust is related to the fluid out, the population pressure, the friction, and the compression force.
4. Applications for three-way control valves
Three-way control valves are commonly used to bypass the regulation of heat exchangers. We can also use them for simple proportional adjustment. A bypass control valve is used to control the temperature of the fluid exiting the heat exchanger by adjusting the bypass volume.
Three-way control valves are fitted to the inlet of the bypass for diversion and to the outlet of the bypass for merging. The flow capacity of a combined flow control valve is greater than that of a shunt control valve. The controlling leader should be aware of temperature differences in the valve.
5. Restrictions on the use of three-way control valves
When using the three-way valve, high temperatures or high-temperature differences will cause the tube to expand. In this case, the three-way valve will produce enormous stress and deformation. It will also cause damage and leakage at the connection. The effects are particularly severe at high-temperature differences. Therefore, we require a three-way valve temperature difference of less than 150 ℃. When the temperature difference is too significant, we can use two two-way valves to replace a three-way valve.
6. The effect of air closure on the actuator
The actuator must be replaced when the three-way control valve is replaced with a gas-open one. The three-way control valve has a straight single-seat control valve and a two-seat control valve. It utilizes the guiding action of the spool so that the spool cannot be used in reverse. Therefore, we can only close the gas with an actuator that acts in the positive direction. When replaced with gas open, we must use the reverse-acting actuator.
The control valve has been in the domestic market has been at the top level. We are constantly innovating the production process. We also adjusted the product structure and improved the regulating valve raw material formula. These make the various performance of the control valve has improved dramatically. We are not just the pursuit of product sales do not seek to improve.
These can show that the control valve industry is an economy full of innovation and vitality. Therefore, we not only pursue the expansion of industrial-scale sales, but we focus on the industry’s future direction.