Once you are through the initial startup, 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, some KP-10s used on
dairy manure may use a 5' extension arm with a hundred pounds of weight.
With some feed materials, the press can be operated with the discharge cone in the
withdrawn position. The screw alone may do enough compressing and dewatering to
produce a cake at the discharge.
It is acceptable to open the discharge cone, in most cases, during normal operating
conditions. This allows inspection, while in operation, of the discharge end of the screw and
screen. This will give the operator a chance to observe operation with minimum dewatering
and maximum throughput. It is also a good technique for purging bad material, i.e. either
jammed or spoiled material, from the press. (Do not try this trick if you are pressing hot or
chemically aggressive materials.)
Where very low air pressure is required for proper operation, it may be practical to put the
cone positioning valve in a neutral position, halfway between open and closed. A press
cannot be left permanently in this condition: keep in mind that a slug of cake will push the
cone open, and it will not re-close on its own afterwards.
An unusual technique is to set the air pressure so that the cone normally stays completely
shut. A timer is used to periodically open the cone. The closed period is determined by the
amount of time required for press cake to accumulate in the press. This type of operation is
used with slippery or slimy press cake that cannot be dewatered to sufficient firmness to
force the cone open. The duration of the "cone open" period is long enough to dump much
of the press cake that has been formed. Vincent Cone Timer panels are available at a
minimal cost.
Once through start-up, the cone is almost always left in the closed position at whatever air
pressure has been found to be effective. A plug of cake will be left around the cone
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