actuator
An actuator is a mechanical device used to control valves, dampers, etc.
　　pneumatic actuator
Pneumatic actuators can provide high stem power output under harsh working conditions. These actuators are typically operated by air pressure, but some can be operated by process liquids themselves.
　　Diaphragm actuator
The action mode of Fisher springs and diaphragm pneumatic actuators can be "positive action", that is, the air entering the diaphragm cover causes the actuator push rod to move downward. This' gas shut-off 'action compresses the spring, which in turn pushes the actuator push rod upwards again when the gas source pressure drops or disappears.
In addition, the action mode of spring and diaphragm pneumatic actuators can be "reaction", that is, the air entering the diaphragm cover causes the actuator push rod to move upward. This "air opening" action compresses the spring, which in turn causes the actuator push rod to move downward when the air source pressure drops. This is the most common type of diaphragm actuator, as the spring will cause the valve to be in the "fault automatic closing" position when the air source disappears.
　　Fisher 657 and 667
Emerson Fisher 657 and Fisher 667, Fisher 657/667 product documentation, Fisher 657/667 product features and advantages, Fisher 657/667 product application specifications
Using spring balanced Fisher 657 and 667 diaphragm actuators, the position of the valve spool is determined by the pneumatic output signal applied to the actuator diaphragm by the controller or valve positioner in response to changes. Fisher 657 and 667 spring diaphragm actuators can locate the position of the valve core in the valve based on the pneumatic output signals from different controllers or valve positioners acting on the actuator diaphragm. The zero position setting of the actuator is determined by the compression amount of the actuator spring. The range can be determined based on the stiffness of the actuator spring and the number of springs provided. 657 is a positive acting executing agency; 667 is a reactive actuator. The design of these actuators enables reliable switching or control of automatic regulating valves.

　Characteristics and advantages
Universal installation - The actuator base has four screw holes for mounting brackets or plates.
Long stroke of actuator - The deep membrane cover uses an actuator with a size of 60, which can achieve a maximum stroke of up to 105 mm (4.125 inches).
Diversified applications - The spring selection range is wide and almost applicable to any control application. The spring selection program is fast and accurate.
Severe operating conditions - sturdy brackets and membrane covers provide stability and corrosion protection.
Regarding the Fisher brand
Emerson Fisher valves provide time tested innovative solutions that can help customers reduce equipment maintenance costs, lower capital requirements, reduce compliance costs, and improve process availability.
This will be achieved through world-class products, including Fisher positioners, Fisher regulators, Fisher control valves, Fisher valves, Fisher regulators, Fisher pressure reducing valves, Fisher control valves, Fisher instruments, and performance services, all of which are the most reliable products in the process control industry.
　　Fisher Company Introduction
Fischer Control Equipment International Limited was founded in 1880. At that time, in Marshalltown, Iowa, USA, our founder William Fisher invented the first pump regulator and planted Fisher's seeds in the small town. Since then, Fisher has achieved tremendous development through years of hard work and has become a recognized brand.
Emerson purchased Fischer in 1992 and merged with another world leader in the process instrumentation field, Rosemount, to establish Fischer Rosemount to better meet our customers' requirements for a complete range of applications and process control. In April 2001, Fischer Rosemount was renamed Emerson Process Management.
　　Fischer's business scope
The industries served include: petroleum and gas, paper and pulp, oil refining, food and beverage, chemical and petrochemical, pharmaceuticals, electricity, metals and smelting, semiconductors; The product and service scope includes: control valves and actuators, digital valve controllers, digital level controllers, AMS ValveLink software, field installed instruments, quick replacement parts services, regulators, etc.