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In order to successfully automate the process, it is most important to ensure that the valve itself can meet the special requirements of the process and the medium in the pipeline. Usually the production process and the process medium can determine the type of valve, the type of valve core, and the structure and material of the valve trim and valve.
After the valve is selected, the next step is to consider the requirements of automation, that is, the selection of the actuator. Actuators can be considered simply in terms of two basic types of valve operation.
Such valves include: plug valves, ball valves, butterfly valves, and dampers or flaps. This type of valve requires an actuator for 90 degree rotation operation with the required torque.
Such valves can be non-rotating poppet stems or rotary non-rising stems, or they require multiple turns of operation to actuate the valve to the on or off position. This type of valve includes: straight-through valve (stop valve), gate valve, knife gate valve, etc. As an option, pneumatic or hydraulic cylinders or membrane actuators with linear output are also available to drive the above valves.
At present, there are four types of actuators, which can use different drive energy and can operate various types of valves.
Electrically driven multi-turn actuators are one of the most commonly used and reliable types of actuators. A single-phase or three-phase motor drives a gear or worm gear and finally drives the stem nut, which causes the stem to move the valve to open or close.
Multi-turn electric actuators can quickly drive large-sized valves. In order to protect the valve from damage, the limit switch installed at the end of the valve stroke will cut off the power of the motor. At the same time, when the safe torque is exceeded, the torque sensing device will also cut off the power of the motor. The position switch is used to indicate the switching state of the valve. A handwheel mechanism fitted with a clutch device allows manual valve operation in the event of power failure.
The main advantage of this type of actuator is that all components are housed in one housing, and all basic and advanced functions are integrated in this waterproof, dustproof, explosion-proof enclosure. The main disadvantage is that in the event of a power failure, the valve can only remain in place, and the valve can only achieve a fail-safe position (fail open or fail closed) with the use of a backup power system.
This actuator is similar to an electric multi-turn actuator, with the main difference that the actuator's final output is 1/4 rotation of 90 degree motion. The new generation of electric single-turn actuators combines the complex functions of most multi-turn actuators, such as parameter setting and diagnostic functions using a non-intrusive user friendly interface.
Single-turn actuators are compact enough to fit on small valves, typically output torques up to 800kgm, and should require less power, they can be battery-installed for fail-safe operation.
Actuators of this type are often used to operate globe valves (stop valves) and gate valves, which use pneumatic or hydraulic operation. The structure is simple, the work is reliable, and it is easy to realize the fail-safe operation mode. MstnLand is a professional globe valves supplier, we produce globe valves with various actuators.
Usually people use electric multi-turn actuators to drive gate valves and globe valves, and hydraulic or pneumatic actuators are only considered when there is no power supply.
Pneumatic and hydraulic single-turn actuators are very versatile, they require no power supply and are simple in structure and reliable in performance. The fields of their application are very wide. Usually the output is from a few kilograms to tens of thousands of kilograms. They use cylinders and transmissions to convert linear motion into right-angle outputs. Transmissions usually include: forks, racks and pinions, and levers. The rack and pinion output the same torque throughout the full stroke range, they are very suitable for small size valves, the fork has high efficiency and high torque output at the start of stroke is ideal for large diameter valves. Pneumatic actuators are generally equipped with accessories such as solenoid valves, positioners or position switches to control and monitor valves.
This type of actuator can easily implement a fail-safe mode of operation.
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