Difference between Fixed Area & Variable Area Flow Meters
With orifice plates flow meters:
- As the rate of flow increases, so does the differential pressure.
- By measuring this pressure difference it is possible to calculate the flow rate through the flow meter.
- The pass area (for example, the size of the hole in the orifice plate) remains constant.
With any type of variable area flow meter:
- The differential pressure remains almost constant as the flow rate varies.
- Flow rate is determine from the position of the float.
- The pass area (the area between the float and the tube) through which the flow passes increases with increasing flow.
Source : spiraxsarco