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27
2021
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Pneumatic actuator classification and selection
Actuator according to its energy form is divided into pneumatic, electric and hydraulic three categories, they have their own characteristics, suitable for different occasions.
Actuator according to its energy form is divided into pneumatic, electric and hydraulic three categories, they have their own characteristics, suitable for different occasions. Pneumatic actuator is a kind of actuator. Pneumatic actuators can also be divided into single-acting and double-acting types: the switching actions of the actuators are driven by the air source and are called DOUBLE ACTING. SPRING RETURN (single action) only on action is air driven, while off action is SPRING reset.
Actuator Selection The purpose of this reference is to help the customer make the correct actuator selection. The following factors must be considered before installing pneumatic/electric actuators into the valve. * Valve operating torque plus manufacturer's recommended safety factor/according to operating conditions. * Air source pressure or power supply voltage of the actuator. Type of actuator double acting or single acting (spring return) and output torque under a certain air source or rated voltage output torque. The correct choice of an actuator is very important. If the actuator is too large, the stem may be overloaded. Conversely, if the actuator is too small, the side cannot generate enough torque to fully operate the valve. In general, we think that the torque required to operate a valve comes from friction between the metal parts of the valve (ball core, disc) and the seal (seat). According to the valve using occasions, the use of temperature, operating frequency, pipeline and differential pressure, flow medium (lubrication, drying, mud), many factors influence the operating torque structure of ball valve is basically based on a polishing ball core (including channel) double in two seat this (upstream and downstream), the rotation of the globe to intercept or fluid flows through the spool, The pressure difference upstream and downstream creates a force that holds the ball core against the downstream seat (floating ball construction). The torque for operating the valve in this case is determined by the friction between the ball core and the seat and the stem and the packing. Maximum torque occurs when pressure difference occurs and the ball core rotates in the closed position toward the open direction of the butterfly valve.
The structure principle of butterfly valve is basically based on the butterfly plate fixed on the axis. Disc is fully sealed with seat in closed position and valve is in full open position when disc is rotated (around stem) parallel to flow direction. Conversely, when the disc is perpendicular to the flow direction of the fluid, the valve is in the closed position. The torque of the butterfly valve is determined by the friction between the butterfly plate and the seat, the stem and the packing. At the same time, the force of the differential pressure on the butterfly plate also affects the operating torque. For example, when the valve is closed, the torque will be significantly reduced after a small rotation. There is a passage in one direction of the plug. The valve is opened and closed as the plug is screwed into the seat. Operating torque is usually not affected by fluid pressure but is determined by friction between the seat and plug during opening and closing. Valve maximum torque when closed. Due to pressure, always maintain high torque for the rest of the operation.
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