How Variable Area Flow Meters Work
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How Variable Area Flow Meters Work Variable area flow meters measure flow by allowing the flow stream to change the opening within the flow meter by moving an internal part. When the flow increases, the fluid generates more force and moves the internal part farther. One variable area flow meter measures flow in a vertical metering tube by balancing the downward weight of a float with the upward force of the flowing fluid. Spring-opposed float designs allow this type of flow meter to be installed in horizontal pipes, because the functioning of the float is not dependent upon gravity. These flow meters can be read locally because their glass or plastic metering tubes have markings that relate the height of the float (that can be seen) with the flow rate of the fluid. Flow meters with remote signals are typically constructed with metal tubes, and include a transmitter that senses the height of the float to determine fluid flow. Vane-style variable area flow meters have a spring-opposed vane that moves in relation to the flow rate. Similarly, piston variable area flow meters use a spring-opposed piston that moves in relation to the flow rate and are less sensitive to viscosity than vane-style variable area flow meters. Both vane-style and piston variable area flow meters can be connected to an indicator or transmitter. |