FAA Powerplant Written Practice Test

Why are two or more springs installed on each valve in an aircraft engine?

1. To increase the pressure on the valve seat

2. To eliminate valve spring vibration or surging

3. To improve the engine's cooling capacity

4. To extend the life of the valves

The correct answer is: To eliminate valve spring vibration or surging

Installing two or more springs on each valve in an aircraft engine primarily serves the purpose of eliminating valve spring vibration or surging. When a valve is opened and closed rapidly, the springs can experience oscillations due to the inertia of the valve and the forces acting on it. This vibration can lead to a phenomenon known as valve float, where the valve does not seat correctly, resulting in loss of performance, increased wear, and potential engine damage. By using multiple springs, the system achieves a more consistent force throughout the valve's operation. This configuration dampens any vibrations that may occur, which helps maintain precise timing in the valve’s opening and closing cycles. The use of dual or multiple springs ensures that even under extreme conditions, such as high RPMs and powerful cylinder pressures, the valves remain securely seated and operate reliably. While increasing pressure on the valve seat, improving cooling capacity, and extending valve life are important considerations in engine design, these aspects are secondary outcomes of using multiple springs. The primary focus is on ensuring stability and reliability in the valve operation.