Principle OF Pneumatic Modulevel Liquid level control
The key elements of the Pneumatic Modulevel Liquid level control are the magnetic coupling, which allows the controller to be mechanically isolated from the sealed sensing unit; the range spring, which dampens the action of the displacer, and the control head, which provides a modulated pneumatic signal in direct proportion to the input from the vertical motion of the displacer.As the liquid level in the vessel increases or decreases, the buoyant displacer rises or falls.This motion, dampened by the action of the range spring to prevent response to the rapid fluctuations of turbulence, is mechanically coupled to an attractor ball, within an enclosed tube. A magnet encircling the tube follows the attractor ball, transferring the motion to a rotating cam,which in turn operates a flapper against a nozzle which increases or decreases the pressure within the pneumatic relay. The output pressure signal can be used in a variety of ways to operate a control valve or signal to alarms, indicators, process controls or other devices. With optional integral control, the pilot nozzle proportional signal is conditioned through an additional metering valve system, which will eliminate offset from the desired control point.
Features of Pneumatic Modulevel Liquid level control
- Standard models handle service temperatures from -100°C to +370°C (-150°F to +700°F) and pressure to 294 bar (4265 PSIG).
- Stable output signal is unaffected by surface turbulence.Prevents control valve “hunting” and extends valve life.
- Controller head may be removed and bench calibrated without dismantling or even depressurizing the tank.
- Accurate output signal provided over a wide specific gravity range.
- 316 SS displacer and trim.
- Easily field calibrated without moving tank liquid level, for reduced installation time and cost.
- Controller head rotates 360°, simplifies pneumatic piping hookup.
- Pilot relay provides a 4 to 1 amplification of pilot pressure signal to speed valve response.
- Built-in visual level indicator is independent of air supply.
- Optional pneumatic to current interface transducer for use in electronic control applications.
- Optional proportional plus integral control.
- Optional differential gap (on-off) control.
- Optional Hi-Lo electronic alarm signal provides inexpensive backup alarm.
Applications of Pneumatic Modulevel Liquid level control
Pneumatic Modulevel® liquid level controls are widely used in utility power generation, chemical and petroleum processing operations, such as:
- Steam generator feedwater
- heater regulation
- Fractionating column level transmitter
- Ethanolamine level transmitter
- Vent gas scrubber level control
- Drip pot condensate level control
- Flash tank level transmitter