OTHER FLOW METERS
The float should stay at a constant position at a constant flow rate. With a smooth float,
fluctuations appear even when flow is constant. By using a float with slanted slots cut
in the head, the float maintains a constant position with respect to flow rate. This type
of flow meter is usually used to measure low flow rates.
In a displacement flow meter, all of the fluid passes through the meter in almost completely
isolated quantities. The number of these quantities is counted and indicated in terms of volume
or weight units by a register.
The most common type of displacement flow meter is the nutating disk, or wobble plate
meter. A typical nutating disk is shown in Figure 7.
Figure 7 Nutating Disk
This type of flow meter is normally used for water service, such as raw water supply and
evaporator feed. The movable element is a circular disk which is attached to a central
ball. A shaft is fastened to the ball and held in an inclined position by a cam or roller.
The disk is mounted in a chamber which has spherical side walls and conical top and
bottom surfaces. The 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, the
disk wobbles, or executes a nutating motion. Since the volume of fluid required to make
the disc complete one revolution is known, the total flow through a nutating disc can be
calculated by multiplying the number of disc rotations by the known volume of fluid.