Glass Tube Rotameter is the most widely used variable area flow

  •   Working principle of Glass Tube Rotameter

      Due to the above advantages, the Glass Tube Rotameter is the most widely used variable area flow meter. It consists of a tapered tube; when fluid passes through the tube, it raises the float. A larger volume flow puts more pressure on the float, raising it higher. In the liquid, the speed of the flowing liquid is combined with the buoyancy to make the float rise; for gas, the buoyancy is negligible, and the height of the float is mainly set by the gas velocity and the subsequent pressure.

      Under normal circumstances, the pipe is installed vertically; when there is no flow, the float stays at the bottom, but once the fluid flows upward from the bottom of the pipe, the float will start to rise. Ideally, the height through which the float moves is proportional to the fluid velocity and the annular area between the float and the pipe wall. As the float rises, the size of the annular opening increases, thereby reducing the pressure difference across the float.

      The system reaches equilibrium and the float reaches a fixed position. When the upward force exerted by the fluid flow balances with the weight of the float-the float is suspended by the fluid flow. You can then read the flow rate of the specific fluid density and viscosity. Of course, the size and composition of the rotameter will depend on the application; if everything is properly calibrated and sized, the flow can be read directly from the scale according to the position of the float. Some Glass Tube Rotameters will allow you to manually adjust the flow rate using a valve. Early designs have free floats that can rotate with changes in gas and fluid pressure; because they rotate, these devices are called Glass Tube Rotameters.

      Glass Tube Rotameter usually provides calibration data and direct reading scales for common fluids (air and water). To determine the size of the rotameter for use with other fluids needs to be converted to one of these standard formats; for liquids, the water equivalent in GPM; for gases, the equivalent in standard cubic feet per minute (scfm) Airflow. Calibration tables for these standard flow values, combined with slide rules, nomograms, or computer software used to determine the size of the rotameter, are usually provided by the manufacturer.

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