FLOWTECH Metal Tube Variable Area Flow Meters (Rotameters) are intended for application where high pressure, temperature OR corrosive conditions preclude the use of conventional glass tube. These are all Metal Variable Area type Flow meter design to measure flow rate of liquids, gases & steam under critical conditions. It consists of a tapered metal tube, an indicating assembly and a float. A magnet encapsulate in float couples with rotating magnets connected to an indicating pointer, thus the movement of the float, is accurately indicated in terms of flow rate.
When fluid or gas flows through a taper tube containing a float, a pressure difference of P1 and P2 is created between upper and lower side of the float. The float moves upwards by a force obtained by multiplying the pressure differential by the maximum cross sectional area of the float.
Due to taper tube, as the float moves upwards, the fluid passing area increases as a result of which the differential pressure decreases. Upward movement of float stops when the dead load is dynamically balanced by the differential pressure. Tapering of metering tube is so designed that the vertical movement of the float becomes linearly proportional to the rate of flow and the scale is provided to read the position of the float, thus giving birth to flow rate indication.
Based on Bemoulli's theorem, the principle mentioned above can be theoretically expressed as follows.