Displacement Meter:

Within a displacement flow meter, all of the fluid passes by the meter in almost fully isolated quantities.  A number of these quantities is counted and denoted in terms of volume or weight units through a register.

Nutating Disk

The most general categories of displacement flow meter are the nutating disk, or wobble plate meter.  A classical nutating disk is display in Figure.

Figure: Nutating Disk

This type of flow meter is generally used for water service, like as raw water supply and evaporator feed. The movable component is a circular disk that is attached to a central ball. The shaft is fastened to the ball and held in an inclined position through a roller or cam. The disk is mounted within a chamber which has spherical side walls and conical top and bottom surfaces. A fluid enters an opening in the spherical wall on one side of the partition and leaves through the other side. As the fluid flows through the chamber and the disk wobbles or executes a nutating motion. Because the volume of fluid required making the disc complete one revolution is known and the total flow through a nutating disc can be calculated through multiplying the number of disc rotations by the known volume of fluid.

To measure this flow, the motion of the shaft generates a cone with the point, or apex, down. A top of the shaft operates a revolution counter, through a crank and set of gears, that is calibrated to indicate total system flow. The variety of accessories, such as automatic count resetting devices, could be added to the fundamental mechanism that performs functions in further to measuring the flow.