Hydraulic tappets (VW Golf 3)

Diesel engines are equipped with so-called "cup" tappets, which have a built-in hydraulic valve clearance compensator. This device eliminates the need for valve clearance control. The valve drive operates without clearances, but nevertheless ensures a tight fit of the closed valves in the seat and high-quality sealing.

Operation of the hydraulic pusher

When the valve is closed, oil from the engine lubrication system enters the tappet through the annular groove. After passing the check valve in the tappet, the oil flows into the filled working cavity (high pressure cavity) and flows back completely).

At the same time, the pusher spring presses without a gap on the distribution chamber or on the cylinder at the end of the valve stem.

When the camshaft rotates and its cam presses the tappet, the pressure in the working chamber increases. The check valve closes the inlet and does not allow oil to leave the working chamber. Since the oil is not compressed, a rigid connection is formed between the tappet and the cylinder. Now the valve can be pressed down by the action of the cam.

After the valve closes, due to oil leakage, a small gap appears in the valve mechanism, but under the action of the spring - it presses the pusher up, it is immediately compensated again. Oil gets into the increased volume of the working cavity with the check valve open again. The hydraulic pusher is ready for the next impact on the valve.

[The original text can be found on the portal: VWManual.ru]