What limits the amount of air drawn from the cross wing manifold?

• A. Pressure relief valve
• B. Manual control valve
• C. Flow limiting venturi
• D. Temperature sensor

Answer: (C)

Flow control in an air system like this is often achieved with a flow-limiting venturi in the supply line. The venturi has a narrow throat that forces the air to speed up as it passes through. When velocity increases, the static pressure drops, and the geometry of the throat sets a fixed relationship between the upstream pressure and the amount of air that can flow through. Because the throat area is fixed, there’s a maximum rate at which air can be drawn into the cross wing manifold, regardless of other conditions. This passive restriction keeps the supply within design limits and prevents surges or overdraw.

A pressure relief valve would only vent excess pressure, not limit the normal draw into the manifold; a manual control valve can restrict flow only when you adjust it, and it isn’t inherently limiting like a venturi; a temperature sensor measures temperature and does not control the quantity of air drawn.