A lifter is also otherwise known as a hydraulic tappet, hydraulic valve lifter, or hydraulic lash adjuster. Essentially, what an engine tappet or valve lifter does is connect the engine's intake and exhaust valves with the camshaft. What this means is that per the rotation of the camshaft, the lifters are responsible for transferring the rotational motion of the camshaft into the vertical motion of the intake and exhaust valves opening and closing. Thus, allowing your engine to control the intake of fuel and air into the combustion chamber. While at the same time, exhausting combustion by-products and fumes out of the engine.