UFC 3-280-03
23 JULY 2003
side of the press. The primary function of this device is to prevent access to the plate
stack while the press is opening or closing. However, for larger presses (i.e., with plates
greater than 1220 mm [48 inches]), it may be necessary to have access to both sides of
the plate stack; therefore, the fixed guards become impractical. For these applications,
a safety light curtain should be employed.
In addition to the fixed safety guards, splash curtains can be used to prevent
access to the plates during operation. Splash curtains are normally temporary structures
that encapsulate the press during the fill cycle or during power washing of the filter
media and plate, or contain high-pressure leakage. Although this can be used as a
temporary safety device, its primary function is housekeeping.
2-4.5.6.2 Light Curtains. The light curtain is optional but is the most commonly used
safety device. A bank of photo cells, on alternative ends of the press, project a
continuous light curtain when automatically activated by the closing or plate shifting
mechanism. If the light curtain is interrupted or broken, the closing or plate shifting is
stopped immediately. The ultimate function of this feature is to prevent workers who are
removing or separating plates or foreign objects from being caught in the press.
Safety light curtains are commercially available in both the visible spectrum
and infrared. An advantage to the visible spectrum curtain is that there is no question
about whether it is operating. If, however, an infrared curtain is used, a beacon-type or
visual light indicator should also be used to provide positive assurance that the curtain
is operating when the plate mechanism is opening or closing. Typically, the horizontal
bank for a light curtain extends from about 0.6 m (2 feet) above the operating floor to
about 1.5 m (5 feet) above the floor, which is the area where an operator might
accidentally get a hand or arm caught between moving plates. However, light curtains
are available that range from the floor upward to the maximum height of the press to
ensure additional operator protection.
2-4.5.6.3 Drip Trays and Bombay Doors. Drip trays and bombay doors are optional,
but important, housekeeping features that can be mounted below the filter press to col-
lect drainage. This drainage may consist of residual filtrate discharged at the end of the
filtration cycle, leakage from the plates during the filtration cycle, and washdown used in
general maintenance and cleaning. Drip trays typically consist of hinged single leaf or
double leaf trays sloped to a launder located on one or both sides and parallel to the
length of the press for drainage. Before the cake is discharged, the drip trays must be
manually slid to one end of the press or removed to prevent them from interfering with
the process of emptying the press.
An automatic equivalent of drip trays that is often used to collect this drainage
is "bombay doors." Bombay doors typically consist of two doors that are automatically
opened and closed by a hydraulic cylinder when the press is opened and closed. These
doors are closed under and parallel to the length of the press. In the open position,
these doors hang vertically and parallel to the sides of the press. The primary
advantage of the bombay doors over the drip trays is they are automated and require
less labor-.
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