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All hydraulic shock absorbers work by the
principle of converting kinetic energy (movement) into
thermic energy (heat). For that purpose, fluid in the
shock absorber is forced to flow through restricted outlets
and valve systems, thus generating hydraulic resistance. |
| A telescopic
shock absorber (damper) can be compressed and extended;
the so-called bump stroke and rebound stroke. |
| Telescopic shock
absorbers can be subdivided in : |
| 1. |
Bi-tube, or twin-tube dampers,
available in hydraulic and gas-hydraulic configuration. |
| 2. |
Mono-tube dampers, also
called high pressure gas shocks.
Bi-Tube Shock Absorbers (fig. A and B) |
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)
- upper and lower attachment |
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|
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How does a Bi-Tube
shock absorber work?
Bump stroke |
| When the piston rod is pushed
in, oil flows without resistance from below the piston
through the orifices A, B, C and D and the non-return
valve (19) to the enlarged volume 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. |
| |
|
 |
Mono-Tube shock absorber.
(fig. C)
The main components are :
- (pressure) cylinder, also called housing
- piston (2) connected to a piston rod (1)
- floating piston, also called separating piston(15)
- piston rod guide (3)
- upper and lower attachment |
| |
How does a Mono-Tube
shock absorber work?
Bump stroke |
| Unlike the bi-tube damper,
the mono-tube shock has no reservoir tube. Still, a possibility
is needed to store the oil that is displaced by the rod
when entering the cylinder. This is achieved by making
the oil capacity of the cylinder adaptable. Therefore
the cylinder is not completely filled with oil; the lower
part contains (nitrogen) gas under 20 - 30 bar. Gas and
oil are separated by the floating piston (15). |
| |
| When the piston rod is pushed
in, the floating piston is also forced down by the displacement
of the piston rod, thus slightly increasing pressure in
both gas and oil section. Also, the oil below the piston
is forced to flow through the piston. The resistance encountered
in this manner generates the bump damping. |
| |
| Rebound stroke |
| When the piston rod is pulled
out, the oil between piston and guide is forced to flow
through the piston. The resistance encountered in this
manner generates the rebound damping. At the same time,
part of the piston rod will emerge from the cylinder and
the free (floating) piston will move upwards. |
