Thorpe tube flowmeter

It consists of a connection to a gas source, a needle valve opened and closed by turning an attached dial for control of flow rate, a float resting in a clear tapered tube, and an outlet port.

The original Thorpe tube flowmeter is the non-compensated type: it works with a fixed orifice and variable pressure.

The non-compensated type is more accurate for low flow rates, such as are used in neonatal units, laboratory experiments, or anaesthetic machines.

In compensated flowmeters, the ball will initially jump as the gas flows through the tube before being released through the needle valve just before the outlet.

No result will be observed in the non-compensated flow meter, as the gas will release before reaching the tapered tube containing the float.