TWIN-TUBE SHOCK ABSORBERS 

The main components are:

• outer tube, also called reservoir tube (6)*

• inner tube, also called cylinder (5)*

• piston (2)* connected to a piston rod (1)*

• bottom valve, also called footvalve (7)*

• piston rod guide (3)*

How Does a Twin-Tube Shock Absorber Work?

Bump stroke.
When the piston rod is pushed in, oil flows without resistance from below the piston through the outlets A*, B*, C*, and D* and the non-return valve (19)* to the area above the piston. Simultaneously, a quantity of oil is displaced by the volume of the rod entering the cylinder. This volume of oil is forced to flow through the bottom valve into the reservoir tube filled with air (1 bar) or nitrogen gas (4-8 bar). The resistance, encountered by the oil on passing  through the footvalve, generates the bump damping.

Rebound stroke.
When the piston rod is pulled out, the oil above the piston is pressurized and forced to flow through the piston. The resistance, encountered by the oil on passing through the piston, generates the rebound damping. Simultaneously, some oil flows back, without resistance, from the reservoir tube (6)* through the footvalve to the lower part of the cylinder to compensate for the volume of the piston rod emerging from the cylinder.