Why concentric springs fitted for auxillary engine cylinder head?
Concentric springs fitted in the cylinder head of the auxillary engine , which helps to open and close the exhaust and suction valve .
The reasons for Concentric springs in the exhaust and suction valves are as follows:-
- If one spring of valve fails then valve will be held up by the other spring.
- The thickness of springs of the suction and exhaust valve can be reduced.
- The space required for one large spring is reduced.
- When the frequency due to the natural vibration of the spring is in harmonic with the speed of the cam shaft, the spring may vibrate axially and cause surge. This can be avoided by using a spring of different size, one inside the other.
- To avoid the side thrust exerted on the spring. One spring is left-handed other is right handed so that the resultant thrust will be zero.
Concentric spring Application
- Because there are two springs, the load-bearing capacity is increased and heavy loads can be transmitted in a restricted area.
- The operation of the mechanism continues in the concentric spring, even if one of the springs breaks. This results in a ‘free failure’ system.
- In the concentric spring, the spring vibrations called the ‘surge’ are withdrawn.
Why two spring in Exhaust valve
If the frequency of the natural vibration of air for exhaust valve springs is a harmonic of the camshaft speed then the spring may vibrate axially and are set to surge . Surge can be avoided by modifying the sizes of Spring by arranging the spring in pairs and fitting one inside the other.
If one spring fails the valve is held up and is not damaged by striking the piston. The thickness of individual spring can be reduced as against original thickness.
Normally two Spring of different vibration characteristic are chosen.
moreover the stiffness requirement and the space condition at this place warrants concentric spring arrangement the net stiffness is equal to the sum of the individual stiffness