ABSTRACT
Inferential-volumetric meters – indirect-volumetric totalisers in which packages of the flowing media are separated from the flow stream and moved from the input to the output – are examined in this chapter. Importantly, the enclosed volume is not geometrically defined but ‘inferred’.
The main discussion centres on the turbine meter in which an axially mounted bladed rotor assembly (the turbine) is mounted concentrically within the flow stream. The rotors may be open bladed (rimless) or shrouded type – the latter is typically used in larger meters – 150 mm and above. The shroud is able to carry small magnetic or paramagnetic buttons that provide greater flow resolution by generating more pulses per unit volume (K-factor).
At low flows, a poor meter response is often due to magnetic drag. This can be overcome by using a Hall-effect device. The use of helical turbines is also considered for improved measurement with high viscosity fluids.
Next, a close look is taken at both flashing and cavitation – with flashing causing the meter to read high and cavitation resulting in rotor damage.
And finally, attention is paid to the Woltman meter, the propeller type meter, and range of impeller meters including the Pelton wheel.
