Hydraulic flat lifter is primarily composed of cylinder, plunger, return spring, and check valve. It relies on the oil pressure oil the high pressure chamber to push plunger up, making effective work time longer and valve lash decreased. The check ball limits the engine oil in high pressure chamber from exhausting, making lifter maintain its expansion length and open the valves.

Hydraulic flat lifter is applicable to engines of OHV mechanism with automatic length compensating thermal expansion at any time, realizing zero lash and reducing noise and impact.