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|  rear lip shall be 9 feet from ground level. The hopper shall be
provided with an emergency draw-off hole in the back, or on either
side, to permit the aggregate to bypass to the receiving hopper of a
portable conveyor by means of an attachable auxiliary chute. The
chute shall have a discharge height of 37 inches plus or minus 1 inch
from the ground. Provisions shall be made for storing the auxiliary
chute on the screening unit. The cover for the emergency draw-off
hole may be a sliding metal plate. The auxiliary chute shall discharge
to the conveyor only when the hopper is mounted on the chassis.
3.10.l.l Hopper grizzly. A remountable grizzly shall be provided
for mounting on the top of the surge hopper. The grizzly bars shall
be high-carbon, heavy duty bars spaced for 3-inch by 12-inch openings.
3.10.2 Reciprocating plate feeder.
The reciprocating plate feeder
shall have a maximum capacity of not less than 150 tons per hour of
dry material, and shall discharge material without spillage onto a
belt 24 inches wide. The feeder shall be driven by a 5-hp electric
rotor.
3.10.2.1 Feeder mechanism. The reciprocating plate shall be
supported on rollers mounted on antifriction bearings. The recipro-
cating plate, rollers, shafts, bearings, and hoppers shall be supported
by structural members and connections. All bearings shall be anti-
friction with labyrinth grease and dust seals; however, the eccentric
bearings may be of the babbitt type. The plate f'ceder may have an
adjustable stroke.
3.10.2.1.1 Feeder bearings. All antifriction bearings shall be
in accordance with FF-B-171, FF-B-185, or FF-B-187, type and class
as applicable. Mounting of the bearings in a manner other than securing
against a shoulder shall be subject to the approval of the contracting
officer for each specific application. Taper-bore bearings are accept-
able when affixed to the shaft by an adapter incorporating a tapered
sleeve and locking nut. Taper-bore bearings need not be secured against
shoulders.
3.10.2.2 Adjustable gate. The feeder shall be provided with a gate
having a height-adjusting mechanism covering the range of capacity from
50 tons per hour (tph) to l50 tph. Changing the feeder stroke to assist
feed-rate variation is permissible, but not less than 50 percent of the
feed-rate variation shall be provided by the gate mechanism. The gate
shall rise automatically to permit passage of oversize rock and shall
then return to the adjusted setting.
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