The ball float method is a direct reading liquid level mechanism. The most practical design for the float is a hollow metal ball or sphere. However, there are no restrictions to the size, shape, or material used. The design consists of a ball float attached to a rod, which in turn is connected to a rotating shaft which indicates level on a calibrated scale (Figure 5). The operation of the ball float is simple. The ball floats on top of the liquid in the tank. If the liquid level changes, the float will follow and change the position of the pointer attached to the rotating shaft.

instrumentation%20and%20control_files/image060.jpg">

Figure 5 Ball Float Level Mechanism

The travel of the ball float is limited by its design to be within 30 degrees from the horizontal plane which results in optimum response and performance. The actual level range is determined by the length of the connecting arm.

The stuffing box is incorporated to form a water-tight seal around the shaft to prevent leakage from the vessel.