US Patent 7621382 Shock absorber

A dampening mechanism is described having a pressure tube defining a working chamber between a rod guide proximate a first end and an end cap proximate a second end. A piston is disposed within the pressure tube and divides the working chamber into an upper working chamber and a lower working chamber. A piston rod is secured to the piston. A reservoir tube surrounds the pressure tube defining a reservoir chamber between the reservoir tube and the pressure tube. At least one passage is disposed through the pressure tube between the reservoir chamber and the working chamber and a bypass valve is disposed between the piston and the at least one passage.