The Valve Operating Mechanisms of Reciprocating Aircraft Engines

A valve is a mechanical component that is often used to regulate, control, and direct the flow of fluids through adjustable orifices and passageways. For reciprocating aircraft engines in particular, valves are crucial for safe and efficient operations as aircraft valves will dictate the flow and pressure of air, fuel, coolants, and more. To ensure that aircraft valves operate as intended and are not held-back by mishaps or improper timing, various valve operating mechanisms are implemented to manage their proper functionality. 

Within radial engines, two or more cam ring components are used to manage the operation of the valve mechanism. When the radial engine features a single row, only one cam ring may be needed with a double cam track. For the management of the intake and exhaust valve, cam rings serve for valve operating mechanism functions. Generally speaking, the cam ring is installed between the propeller reduction gearing and the power section’s front end, though such parts may also be present between the rear end of the power section and supercharger section in the case of a twin-row radial engine.

For the valve mechanisms of opposed engine types, camshafts are used to facilitate operations. Camshafts are rotating metal objects that feature pointed cams, and they may be used to transform rotational motion into reciprocal motion. Within the opposed engine, the camshaft is driven by connected gears that are attached to the crankshaft. With the assembly of components, the camshaft is designed to have a rotational speed that is half of the crankshaft’s speed. As the crankshaft rotates the camshaft through gears, lobes will actuate a tappet assembly and cause it to rise. With the rising of the tappet assembly, force will be transmitted through a push rod and rocker arm in order to open a valve.

Generally, a tappet assembly is used within aircraft engines in order to convert rotational motion into reciprocating motion to operate the push rod, rocker arm, and then the valve itself. Across engine configurations, a tappet assembly will consist of a cylindrical tappet, tappet roller, tappet ball socket or push rod socket, and a tappet spring. By drilling a hole into the tappet, engine oil can flow through the assembly and lubricate the rocker and its related components.

When utilizing solid lifters and cam followers for an aircraft engine, the valve clearance requires manual adjustments through the use of a screw and lock nut. By adjusting the clearance of such aircraft valves, aircraft engine valvetrain parts will be able to close correctly. With hydraulic valve tappets and lifters on the other hand, valve clearance is automatic.

With the use of the push rod, the valve tappet assembly’s lifting force can be transmitted to the rocker arm. Tubular in construction, the push rod is encased within a housing that extends from the cylinder head to the crankcase. With the rocker arms, the cam’s lifting force is then transferred to the valves. With plain, roller, or ball bearings, the rocker arm is facilitated in its movement and can pivot. To ensure that aircraft engine valvetrain parts are able to close fully, the rocker arm may feature an adjusting screw to change clearance.

Lastly, valves rely on a number of springs to open and close efficiently. Typically, two or three springs are common for aircraft valves, ensuring that vibration and surges do not occur during engine operation. By adding redundant springs, the valve can also be better protected from component failures in the case of a spring breakage.

With the use of camrings, camshafts, push rods, rocker arms, and aircraft engine valvetrain parts, aircraft valves can be efficiently operated to facilitate the functionality of the engine. At Aviation Parts Circuit, we serve as a leading online distributor of aircraft parts with over 2 billion items sourced from top global manufacturers. Utilizing our market expertise and purchasing power, we provide customers with time and cost savings for their benefit. To experience how Aviation Parts Circuit is revolutionizing the part procurement process, fill out and submit an Instant RFQ form and a dedicated account manager will reach out to you in 15 minutes or less.


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