4
Rebound damping
When the spring presses the shock absorber out
again, the fluid flows back through the needle
valve in the piston rod. The fluid flowing into the
chamber is forced by the pressure of the gas back
into the shock absorber via a separate non return
valve. If velocity of the piston is high, the shims
on top of the piston will also open to allow the
fluid to flow though.
Function
The function, in principle, is that fluid is forced
through needle valves at a low rate of flow (Fig.5)
and through a number of apertures in the piston
at a high rate of flow (Fig.6). The flow through these
apertures is regulated by shims (thin steel wash-
ers) that at high pressure are deflected to open for
the fluid (Fig.7). On some models the needle valves
can be set individually (illustration).
By altering the size of the shims-stack (ie,
number, thickness, diameter) (Fig.8) the
characteristics of the damping action can be varied
(this shall only be done by Öhlins authorized
service workshops).
Compression damping
When movement of the vehicle causes compres-
sion in the shock absorber, the fluid flows through
the needle valve (combined compression and return
valve) in the piston rod. If velocity of the piston is
high, ie, in the case of rapid compression, this will
not be sufficient and consequently the shims
underneath the piston will open to allow a greater
rate of flow.
The fluid that is displaced by the volume of the
piston rod is forced into the external fluid chamber
via a separate compression valve. Even this valve
is fitted with shims that open at high piston
velocity. The separating piston is displaced, thus
increasing the gas pressure.
5. Flow through
needle valve
6. Flow through piston
7. Shim stack
8. Shim stack
Compression flow
Rebound flow
Stop washer
Shims stack
Piston
Summary of Contents for 07235-01A5L.p65
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