The working principle of a hydraulic tappet
Hydraulic valve lifter parts
1 – retaining ring; 2 – plunger; 3 – cylinder; 4 – check valve; 5 – spring; 6 – body
The use of hydraulic tappets ensures automatic compensation of valve clearances during operation.
Under the pressure of the spring, the plunger and cylinder move away from each other, due to which the gap between the camshaft cam and the valve wire lever is selected. The high-pressure chamber is locked by a check valve.
When the camshaft cam hits the end of the tappet, the check valve closes the chamber and the pressure in it increases. The tappet thus works as a solid body.
When the cam is at its maximum lift, it presses hard on the tappet, which causes a significant increase in pressure in the tappet cavity. A small amount of oil is ejected through the gaps between the cylinder and the plunger, which causes the hydraulic tappet to compress (maximum 0.10 mm).
As the camshaft turns further, the cam stops pressing on the tappet and the pressure inside the tappet drops. The spring separates the plunger and the cylinder, thereby selecting the gap between the cam and the valve lever. At this point, the check valve opens and some oil from the oil line enters the high-pressure chamber. This amount depends on the size of the selected gap.
The pusher can be disassembled after removing the retaining ring. However, if the pusher malfunctions after long-term use, it is recommended to replace the pusher completely.
When hydraulic tappets are used, the seat in the cylinder head usually wears out and the head needs to be replaced.
If there are signs of wear on the surface of the tappet that contacts the camshaft cam, the tappet must be replaced, since grinding the surface reduces the overall length of the tappet, which will change the valve clearance adjustment conditions.