Direct acting actuator (spring-to-retract)The direct acting actuator is designed with the spring below the diaphragm, having air supplied to the space above the diaphragm. The result, with increasing air pressure, is spindle movement in the opposite direction to the reverse acting actuator.The effect of this movement on the valve opening depends on the design and type of valve used, and is illustrated in Figure 6.6.3. There is however, an alternative, which is shown in Figure 6.6.4. A direct acting pneumatic control actuator is coupled to a control valve with a reverse acting plug (sometimes called a 'hanging plug').
Level Sensors Level Switches Level Transmitters Liquid Level Controllers - Electric Liquid Level Controllers - Pneumatic Pneumatic Pressure Controllers Differential Pressure Energy Responsible Controller Gauge Pressure High-Low Pilot Pneumatic Temperature Controller Valve Accessories Pneumatic Pressure Controllers Once again Emerson Process Management reinforces its long-standing commitment to technological excellence with a complete line of pressure controllers. Simplicity…ruggedness…reliability - these are the qualities that have made Fisher® products the industry standard in pressure control. These controllers bring you economical and accurate control whether the process variable is differential pressure (at either low or high static pressures) or gauge pressure. Their simple, yet rugged construction pays off in long, reliable service under difficult operating conditions. Differential PressureDifferential pressure controllers use either a bellows or a capsular element for sensing two different pressures. The difference between these pressures is then compared to an operator-adjusted set point.Energy Responsible ControllerFisher products compare sensed process or differential pressure and send a pneumatic signal to an adjacent control element that maintains the process pressure at or near the set point value.Gauge PressureGauge pressure controllers measure the difference between the absolute pressure and the local atmospheric pressureHigh-Low PilotThe Fisher high-low pressure pilot product offering maintains full output when the process is within the set point range. If the process moves outside of this range, the pilot switches to zero output.
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