Under the pressure of spring 9, the plunger and cylinder move away from each other, due to which the gap between the camshaft cam and the end of the valve stem is selected.
Filling and locking of the high-pressure chamber 8 is ensured by the check valve 3.
Sectional view of hydraulic tappet: 1 — camshaft cam; 2 - pusher; 3 - check valve; 4 — cylinder; 5 - accumulation chamber; 6 — valve; 7 — oil feed roller to the pusher; 8 - high pressure chamber; 9 — valve clearance compensation spring.
(A link to the original source is available on the website audimanual)