How does a Thorpe Tube function in measuring oxygen flow?

A Thorpe Tube functions by utilizing a flow variable orifice, which is the principle behind its design. In a Thorpe Tube, a float within a tapered glass tube rises or falls in response to the flow of gas, specifically oxygen in this context. As the flow rate increases, the float moves up, creating a larger area for gas to pass through, which is determined by the position of the float. The higher the flow rate of the gas, the higher the float rises, allowing for direct visual measurement against calibrated markings along the tube.

This design allows for a clear, instantaneous reading of the flow rate, making it very effective for adjusting and regulating gas flow in medical settings. The variable orifice aspect is critical because it changes in size based on the gas flow, thus providing accurate flow measurement across different conditions.

In comparison, a fixed pressure flow device would maintain a constant pressure regardless of flow changes, and gravity-based flow meters rely on weight, which is not applicable here. An adjustable pressure gauge measures pressure rather than flow, making it unsuitable for the purpose of measuring flow rates accurately like the Thorpe Tube.