Metal tube Variable Area Flowmeters
Variable Area Flowmeter measures volumetric flow rate of liquid and gases that operates on the float principle. It features a tapered metal tube, in which a float is allowed to move freely up and down. The float reaches a stable position when the upward force exerting by the flowing liquid equals the weight of the float. The float position is transmitted by a magnetic coupling system to the scale. The rotational movement of the follower magnet system transmitted to the indicator is linearised and the flow rate is indicated directly on the scale.
Image Courtesy : Brooks
The ﬂow path has a tapered part. A ﬂoat containing a magnet is located in the tapered tube. Fluid flows from the bottom of the flowmeter and goes upward through the tube.
The differential pressure produced by the float and the tapered tube pushes the float upward, and the float stops when the weight of the float and the diﬀerential pressure balance. In other words, the position of the float corresponds to the flow rate.
The movement of the magnet in the float is detected by the magnetic coupling, which converts it into the movement of the pointer.
Although the tapered tube and thread part are welded by braze pressure welding (BPW) with high-frequency induction heating, TIG welding may be used in some speciﬁcations.
Source : tokyokeiso.co.jp