Valve spring

The valve spring , attached to the valve stem with a spring washer and split keeper,holds the valve closed.
it is mostly a helical spring used to close the poppet valve and maintain an air-tight seal by forcing the valve to The valve seat .

A spring accumulates kinetic energy during
contraction and the energy is dissipated upon
expansion.

At low Camshaft revolutions, the valve spring
can follow the valve lift easily so that the valve
moves regularly. By contrast, at high revolutions,
it is more difficult for the valve and valve spring
to follow the cam.

Valve float is the term given to unwanted
movements of the valve and valve spring due
to their inertial weights. to avoid this,the load
of the valve spring should be set high.

The load applied at the longest length is called
the set load,and the valve spring is always set
to have a high compressive stress above set
load conditions.

Another resistance phenomenon that occurs at high revolutions is surging ,due to resonance.

Surging occurs when each turn of The coil spring vibrates up and down at high frequency,
independently of the motion of the entire spring.

It takes place when the natural frequency of the valve spring coincides with the particular rotational
speed of the engine . Generally , surging occurs at high revolutions , and the surging stress generated
is superimposed on the normal stress.

The total stress is likely to exceed the allowable fatigue limit of the spring material and can break
the spring.

A variable pitch spring reduces the risk of surging . This spring has two portions along the length,
a roughly coiled portion and a densely coiled portion , which ensures that the natural frequency of the
spring is not constant and therefore not susceptible to resonance.