Operation of Hydraulic Tappets

With the valve closed, oil from the engine lubrication system enters the bucket tappet through the annular groove. After passing the check valve, the lubricant enters the still empty high-pressure chamber and completely fills it.

In addition, the spring presses the bucket tappet against the camshaft.

When the camshaft rotates and its eccentric cam presses on the bucket tappet, pressure builds in the chamber. The check valve closes the inlet opening, so the oil cannot escape. Since oil is incompressible, a rigid connection is established between the bucket tappet and the cylinder. That is, the valve is forced downward by the cam.

After the valve closes, a small clearance forms due to oil leakage; however, it is immediately compensated by the compression spring, which pushes the bucket tappet upward. Oil flows back into the increased volume of the high-pressure chamber through the open check valve. The hydraulic tappet is thus ready for the next valve actuation.