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During initial, first-time, start up, presses with air cylinder actuators are generally
started up with the discharge cone in the withdrawn position. This will avoid an
unnecessary jam.
With the air cylinder models, the discharge cone mechanism can readily be
positioned in the "open" (withdrawn or "out") position.
Note that with many materials it is necessary to start the press with the discharge
cone in the closed position at low air pressure. Thin or soupy materials, like
pumped manure or clarifier underflow, can tend to purge right through the press if
the press is operated with the discharge cone open (in the withdrawn ("out")
position).
However, with materials that are dry to begin with, such as sawdust or plastic wash
tank sludge, it becomes more important to start with the discharge cone in the open
position. This is because these materials may tend to jam or overload the press.
Similarly, high freeness materials, from which the water falls away freely, will have
a tendency to jam in a press. Be sure to start the press with the cone open, and
gradually close it with low air pressure, when running such materials for the first
time.
Once you are through the initial start up, it will be unlikely that your press should
have the cone opened before starting. Most operators rarely open or shut the cone
once it is set.
As the pressure on the discharge cone is increased, not only will the cake become
drier, but the flow through the press may also be reduced. With very slippery or
slimy feed material it may be possible to apply enough discharge cone pressure to
stop the flow altogether.
High discharge cone pressures can result in increased quantities of suspended
solids in the press liquor.
Care must be taken if a press is to be left running at a very low pressure like 10 psi. If
some fiber enters between the cone bushing and the screw shaft, it will take more
than that much pressure to close a cone which has been pushed open by a heavy
flow of cake. The result will be either high moisture content in the cake or, worse,
purging.
On models without air cylinders, weights used to actuate the discharge cone vary
considerably. When dewatering food waste there may be a need to minimize the
amount of solids being forced through the screen. At the other end of the scale,
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