What type of valves are the 5th- and 10th-Stage Bleed Air Valves?

• A. Piston-type.
• B. Ball-type.
• C. Globe-type.
• D. Needle-type.

Answer: (A)

Piston-type valves are used for the 5th- and 10th-stage bleed air paths because they provide strong, reliable shutoff along with smooth, proportional control over a wide range of flow at high pressures. In these bleed systems, precise metering of compressor air is needed to feed anti-ice, cabin pressurization, and other systems, and the piston design moves linearly to open or close a passage, giving predictable flow as the actuator position changes. The seals around the piston offer tight leakage control, which is important for preventing unwanted bleed leaks when the valve is closed.

Ball-type valves would require rotating a spherical ball to seal, which isn’t as conducive to precise throttling in the high-velocity, high-pressure bleed paths. Globe-type valves can throttle but add more flow resistance and weight, and aren’t as compact or rapid to respond as a piston actuator setup. Needle-type valves are suited for fine metering of small flows, not the large, variable bleed flow these stages handle.