Flow meters and flow measurement have been around for thousands of years, with early versions of the instruments found as far back as the Roman Era. The rudimentary meter was enhanced in the 17th century after the mathematical foundations of flow theory evolved. Today, the variety of flow meter styles has greatly expanded from those early beginnings. Some examples include variable area, positive displacement, ultrasonic and mass flow meters. Each type of flow meter has distinct features that complement use in the corresponding application and industry. End users need to know how to choose the right flow meter for their specific application. The variable area flow meter can be a cost-effective solution for many applications. The meter measures fluid flow by allowing the device’s cross-sectional area to vary in response to the flow, causing a measurable effect on the rate. The variable area flow meter offers many advantages over some more technologically advanced types, making it the meter of choice for many flow-measurement applications.
This type of technology can be a cost-effective solution for many applications.
Blue-White Industries
04/26/2017
Figure 1. Fluid through a variable area flow meter forces the float upward to indicate flow rate. (Graphic courtesy of Blue-White Industries)
The flow meter body is a vertically tapered tube, allowing fluid to pass from the smaller end to the larger end of the taper.
As the fluid flows through the tube, it forces an indicator (float) upward. The clearance space (the annular area between the float and tube wall) increases as the float moves toward the top of the meter.
The larger clearance area toward the top requires a larger volume of fluid to force the float higher. The greater the flow, the higher the float is raised.
Different flow ranges can be calibrated by varying the taper of the tube, the mass of the float and the length of the tube.
A scale with flow increments or measurements is typically printed next to the tube or on to the tube itself. The flow rate can be read by matching the increments on the calibrated scale with the edge of the float.
Proper installation of the variable area flow meters is critical to performance. The meter must be plumbed into the piping system with the narrow part of the taper at the bottom (inlet).
See other Flow Meters articles here.