Which part of the flowmeter is responsible for controlling gas flow?

• A. The orifice
• B. The flow tube
• C. The needle valve
• D. The control knob

Answer: (C)

The needle valve plays a crucial role in regulating gas flow within the flowmeter. It allows the user to fine-tune the amount of gas being delivered by adjusting the valve's position, thereby controlling the flow rate. When the needle valve is turned, it either opens or closes the pathway through which the gas flows, enabling precise control over the gas delivery—critical for ensuring accurate dosages during anesthesia.

The orifice is a fixed opening through which the gas can flow but does not provide any means of adjustment. The flow tube measures the flow but does not influence it directly. The control knob is used to manipulate the needle valve, but the actual control of flow is accomplished by the functioning of the needle valve itself. Therefore, understanding the role of the needle valve is essential for comprehending how gas flow is managed within anesthesia machines.