They also help parts such as the engine, the axle last longer.
Basic twin tube
The twin tube contain to nested cylindrical tubes. One is called the working tube and the other is called the reservoir. Both the tubes contain hydraulic fluid. A piston is inserted into the inner tube and the piston cap has tiny orifices for the hydraulic fluid to get displaced when the piston pushed to and fro. The basic twin tube uses the principle of transferring kinetic energy to heat energy to offer resistance in motion. But when the bumps make the piston move up and down rapidly, air bubbles form behind the piston. This is called cavitation, and it causes aeration and fluid foaming.
Twin-tube gas charged
In the overall, this is very similar to the basic twin tube, but contains nitrogen gas in the reservoir instead of hydraulic fluid. This is a major improvement over the basic twin tube, as it gets rid of problems like aeration and foaming and also hydraulic fluid dripping out of the pipe caused by the action of the piston. Due to this prevention, overheating is reduced largely.
Position sensitive damping
Also known as PSD, position sensitive damping system contains two extra grooves, so that the piston moves freely on the tube, if the vehicle is running on a smooth surface. But at the same time, it also restricts the movements when the vehicle moves in a bumpy surface, where the upward and downward movement of the piston occurs with more intensity. This new advancement made in the dampening system enabled car designers to manufacture shock absorbers according to the size, weight, maneuverability, etc. of the car.
Acceleration sensitive damping (ASD)
This is the next step in the damping system. An acceleration sensitive damping can change behaviors between smooth and bumpy riding. It can also react to bumps individually. ASD is achieved by making some changes in the compression valve. The important thing to note here is that, this damping mechanism just doesn’t improve on the regular ‘control vs comfort’ trade off, but rather eliminates it. It also highly reduced the pitch of the vehicle while braking and roll during turning.
The mono-tube
Unlike the bi-tube damper, the mono-tube shock has no reservoir tube. There has to be an amount of displacement of the hydraulic fluid when the piston is pushed in. This is managed by making the fluid adaptable to pressures. This is achieved by filling the lower part of the tube with nitrogen gas. The hydraulic fluid and nitrogen gas are separated by what is called a ‘floating piston’.
When the piston is pushed downward, pressure arises in both hydraulic fluid and nitrogen. But as an act of displacement, the floating piston moves downward compressing the nitrogen gas.
Likewise, when the piston is pulled out, the hydraulic fluid flows through the piston and the floating piston is also lifted upwards. The resistance created this way offers outbound damping of the suspension.