Lesson 3/Learning Event 1
The direct-acting shock absorber is double-acting.
When the vehicle spring is
compressed, the shock absorber telescopes in (gets shorter). This moves the piston down,
putting pressure on the oil under the piston. For the piston to continue to move
downward, it is necessary for the oil to pass through the compression valve. Oil flows
through the compression valve into the upper section of the inner cylinder. Oil flow and
spring compression are regulated by the size of the compression valve port holes and the
When the spring rebounds, the piston is moved up and down. The oil trapped above the
piston must travel through the rebound valve. To make up for the reduced amount of
rod that is now in the inner cylinder, additional fluid is pulled in from the reservoir
through the intake valve. Oil flow and spring movement is regulated by the size of the
rebound valve opening and its spring. Sometimes a series of valves is used to provide
better regulation of the oil flow in the shock absorber to produce a smoother ride.