Wiv: Measurement of Flow of Gases

Vertical conical measuring tube, which gets wider as you go up

Bobbin which can move up and down

The bobbin and conical tube create a variable ring orifice

The higher the bobbin, the larger ring orifice

When there is no flow, gravity keeps bobbin at bottom of conical measuring tube

As gas flow commences, the bobbin rises, until the opposing forces are in balance:

3 forces:

gravity – downwards

buoyancy – upward

drag (flow force) – upward

Gravity and Buoyancy are constant

Only flow force varies

Position of bobbin indicates the change in flow