Overview and principles of various valves, you will understand after reading (2)
Regulating valve, also known as control valve, is a final control component in the field of industrial automation process control that changes process parameters such as medium flow rate, pressure, temperature, and liquid level through power operation by receiving control signals output from the regulating control unit. It is generally composed of an actuator and a valve. If according to the characteristics of the stroke, the regulating valve can be divided into straight stroke and angular stroke; According to the power used by the actuator, it can be divided into three types: pneumatic control valve, electric control valve, and hydraulic control valve; According to its function and characteristics, it can be divided into three types: linear characteristics, equal percentage characteristics, and parabolic characteristics. Regulating valves are suitable for media such as air, water, steam, various corrosive media, mud, oil, etc. English name: control valve, the tag usually starts with FV. Common classification of regulating valves: pneumatic regulating valve, electric regulating valve, hydraulic regulating valve, self operated regulating valve.
2. Check valve
A check valve is a valve that automatically opens and closes by the force of the fluid itself, and its function is to prevent the backflow of the medium. It has many names, such as check valve, one-way valve, single flow valve, etc. According to structure, it can be divided into two categories.
Lift type: The valve disc moves along the vertical centerline of the valve body. There are two types of check valves: one is horizontal, installed in horizontal pipelines, with a valve body shape similar to a globe valve, and the other is vertical, installed in vertical pipelines.
Swing type: The valve disc rotates around the pin axis outside the seat. This type of valve can be single, double, or multi disc, but the principle is the same.
3. Pressure reducing valve
A pressure reducing valve is a valve that adjusts the inlet pressure to a desired outlet pressure, and relies on the energy of the medium itself to automatically maintain a stable outlet pressure. From the perspective of fluid mechanics, a pressure reducing valve is a throttling element with variable local resistance. By changing the throttling area, the flow velocity and kinetic energy of the fluid are altered, resulting in different pressure losses and achieving the purpose of pressure reduction. Then, relying on the adjustment of the control and regulation system, the fluctuation of the pressure behind the valve is balanced with the spring force, so that the pressure behind the valve remains constant within a certain error range.
The pressure reducing valve mainly controls the fixed outlet pressure of the main valve. The outlet pressure of the main valve does not change due to changes in the inlet pressure, nor does it change due to changes in the outlet flow rate of the main valve. Suitable for industrial water supply, fire water supply, and domestic water pipe network systems.
4. Throttle valve
A throttle valve is a valve that controls fluid flow by changing the throttle section or length. Parallel connection of throttle valve and one-way valve can be combined to form a one-way throttle valve. Throttle valve and one-way throttle valve are simple flow control valves. In a quantitative pump hydraulic system, the combination of throttle valve and relief valve can form three types of throttling speed control systems, namely inlet line throttling speed control system, return line throttling speed control system, and bypass throttling speed control system. Throttle valves do not have negative flow feedback function and cannot compensate for speed instability caused by load changes. They are generally only used in situations where load changes are not significant or where speed stability requirements are not high.
Due to the fact that the flow rate of the throttle valve depends not only on the size of the throttle area, but also on the pressure difference before and after the throttle, the stiffness of the valve is small, so it is only suitable for situations where the load change of the actuator is small and the speed stability requirement is not high.
For throttle speed control systems with large load changes in the executing components and high requirements for speed stability, pressure compensation must be performed on the throttle valve to maintain the pressure difference before and after the throttle valve unchanged, thereby achieving flow stability.
A check valve is a valve that automatically opens and closes by the force of the fluid itself, and its function is to prevent the backflow of the medium. It has many names, such as check valve, one-way valve, single flow valve, etc. According to structure, it can be divided into two categories.
Lift type: The valve disc moves along the vertical centerline of the valve body. There are two types of check valves: one is horizontal, installed in horizontal pipelines, with a valve body shape similar to a globe valve, and the other is vertical, installed in vertical pipelines.
Swing type: The valve disc rotates around the pin axis outside the seat. This type of valve can be single, double, or multi disc, but the principle is the same.
3. Pressure reducing valve
A pressure reducing valve is a valve that adjusts the inlet pressure to a desired outlet pressure, and relies on the energy of the medium itself to automatically maintain a stable outlet pressure. From the perspective of fluid mechanics, a pressure reducing valve is a throttling element with variable local resistance. By changing the throttling area, the flow velocity and kinetic energy of the fluid are altered, resulting in different pressure losses and achieving the purpose of pressure reduction. Then, relying on the adjustment of the control and regulation system, the fluctuation of the pressure behind the valve is balanced with the spring force, so that the pressure behind the valve remains constant within a certain error range.
The pressure reducing valve mainly controls the fixed outlet pressure of the main valve. The outlet pressure of the main valve does not change due to changes in the inlet pressure, nor does it change due to changes in the outlet flow rate of the main valve. Suitable for industrial water supply, fire water supply, and domestic water pipe network systems.
4. Throttle valve
A throttle valve is a valve that controls fluid flow by changing the throttle section or length. Parallel connection of throttle valve and one-way valve can be combined to form a one-way throttle valve. Throttle valve and one-way throttle valve are simple flow control valves. In a quantitative pump hydraulic system, the combination of throttle valve and relief valve can form three types of throttling speed control systems, namely inlet line throttling speed control system, return line throttling speed control system, and bypass throttling speed control system. Throttle valves do not have negative flow feedback function and cannot compensate for speed instability caused by load changes. They are generally only used in situations where load changes are not significant or where speed stability requirements are not high.
Due to the fact that the flow rate of the throttle valve depends not only on the size of the throttle area, but also on the pressure difference before and after the throttle, the stiffness of the valve is small, so it is only suitable for situations where the load change of the actuator is small and the speed stability requirement is not high.
For throttle speed control systems with large load changes in the executing components and high requirements for speed stability, pressure compensation must be performed on the throttle valve to maintain the pressure difference before and after the throttle valve unchanged, thereby achieving flow stability.
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