Fork Working - Marzocchi MAGNUM Handbuch

FORK WORKING (see pictures on page 33-34)
Here only the hydraulic fork working features will be considered, without dealing with the
spring function, which is in each leg and plays a decisive role with respect to the fork
reactions against stresses. In order to give a better explanation on how the suspensions
work, the moving parts (halftone) are different from the parts fixed to the cycle frame; any
oil flowing or movement in the different working stages is represented by means of arrows.
Each fork leg is formed by a cartridge (1, FIG. A) with an inner pumping element (2, FIG.
A) secured to the upper plug (4, FIG. A) of the stanchion tube by means of a rod (3, FIG.A).
An adjustment knob is on the plug. This shuts the flowing area of the fluid coming from the
cartridge by means of a conical pin (5, FIG. A). The pumping element is equipped with
washers which by-pass the oil flowing.
The structural arrangement of the pumping elements is characterized by a multivalve
system which allows all the fork working parameters to be kept under control in the different
use conditions and, at the same time, allows an aimed intervention without changing the
existing configuration. This system also avoids any dangerous cavitation effect often
occurring in forks where the fluid flows through one or two critical points.
Let's see what happens in a (L.H.) COMPRESSION leg if riding on an uneven track (a, FIG.
A).
– the oil in the damper cartridge is pushed downwards by the pumping element and flows
through the 5 holes in the control cylinder without any problem. This fluid mixes with the
fluid coming from the adjustment unit in a depressurized chamber (in practice at
atmospheric pressure);
– under this condition the washers on the pumping element piston are still completely
closed and the fluid volume flowing through the adjustment pin is not important with
respect to the fluid flowing through the 5 holes;
– for this reason, the result will be a not very braked fork able to absorb the small
unevenesses of the track.
Let's see what happens in presence of some remarkable obstacles, such as a series of
bumps (b, FIG. A):
– a big part of the damper rod goes into the damper cartridge, thus leading the pumping
element to go beyond the two upper holes so that a smaller quantity of oil can flow
through the three open holes in the control cylinder.
– the oil pressure is not enough to wear down the resistance of the pumping element
washers and, at this stage, the position of the conical pin of the adjustment unit shutting
the fluid flowing through the upper valve plays a major role;
– in this way a more braking response of the fork is obtained, above all dependent upon
the smaller outlet area of the fluid and the adjustment unit position.
Now let's see what happens inside the leg during a violent compression caused by a big
obstacle (c, FIG. A):
– the pumping element unit goes beyond all the fluid outlet holes of the control piston and
the oil pressure opens the washers on the piston so that it goes into the chamber over
the pumping element which communicates with the depressurized area;
– at this point, the area where the fluid flows through the pin valve plays a major role;
– the result will be a very braked fork and this condition can be increased or decreased
by means of the adjustment unit.
In the (R.H.) REBOUND leg the foot valve (6, FIG. B) is very important. It meters the
damper cartridge filling, it is at the sliding unit end and has washers.
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