Graco S20 Operation page 20

Supply System Overview
Blowoff Button (BG)
Blowoff air will vent between the platen (D) and the
drum when the platen exits the drum, causing noise
and potential material splatter. Wear appropriate
protective equipment to help prevent serious injury
from potential material splatter when the platen exits
the drum.
The supply system uses the ram cylinders to lift the
displacement pump (C) and platen (D). Blowoff air is
used to push the material drum off of the platen as the
ram rises.
Pressing the blowoff button (BG) forces air between the
drum and platen (D) to push the drum off the platen.
Without blowoff air, the platen (D) will remain in the
drum when raising the ram, causing the drum to lift off
of the ram base. When the ram director valve (BC) is
moved to the UP position, pressing the blowoff button
(BG) will force air under the platen to push the drum off
of the platen and maintain contact between the drum
and the ram base as the ram is raised. It is necessary to
coordinate the rate that the ram lifts with the rate that
the blowoff air pushes the drum off of the platen to
keep the drum in contact with the ram base. Keeping
the drum close to or in contact with the base of the ram
will ensure the drum stays upright and does not tilt on
the platen. In order to keep the platen moving upwards,
and also pushing out of the drum, the blowoff button
(BG) needs to be pulsed, as explained in the Drum
Change Procedure on page 25.
The ram director valve (BC) must be at least halfway
between the NEUTRAL and UP position for blowoff air
to pass. The lifting speed of the ram can be increased
by moving the ram director valve (BC) closer to the full
UP position, and decreased by moving the ram director
valve (BC) closer to the neutral position. A hissing
sound can usually be heard in the drum when blowoff
air is passing.
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