TM 5-810-15
lights tell the operator at the control panel which
abrasion resistant and bolted for easy replacement.
piece of equipment has tripped and also the reason.
(6) Motor operated gates and valves will be
hardness of the conveying chain.
e. Drive sprockets. Provide a segmental type
provided in locations requiring frequent operation,
and properly interlocked for starting and stopping
with reversible teeth sections, so that the complete
in the proper sequence.
drive shaft assembly does not have to be removed
b. Computerized
control
systems.
A
for maintenance. Teeth hardness will match chain
computerized control system such as a
hardness.
programmable controller (PC) is the most cost
effective where logic functions must be
5-27.
Pneumatic conveying systems.
accomplished. Advances in micro technology make
a. General. Pneumatic conveying involves the
the cost of computer type controls more
movement of powdered, granular or other free
economical than the relay based control systems.
flowing bulk materials along the pipeline with the
Field changes to the logic in a PC system can be
aid of compressed air. Pneumatic conveying can be
made without wiring changes. Most units allow a
very basically categorized into two areas--dense
program simulation mode, whereby the PC will
phase and dilute phase. Suitable materials that can
diagnose the program and check the logic that has
become fluid-like or fluidized are usually only
been entered. The computerized system is the
suitable for pneumatic conveying. The product size
preferred method of control.
can also restrict the use of this type of conveying
medium. This type of system is sometimes used for
5-26.
En masse conveying system.
moving small tonnages, up to about 50 tph.
a. General. This type of system uses a conveying
(1) Materials that have a high moisture con-
chain which utilizes the skeletal flight as opposed to
tent, such as wet coal are difficult if not impossible
a paddle flight, which can greatly reduce the
to handle in a pneumatic type system.
horsepower requirements for the conveyor. The
(2) Pneumatic conveying systems are ex-
conveyor chain runs in a completely enclosed and
tremely inefficient when comparing tonnage moved
sealed trough. The effective conveying capacity can
to hp required to move the material with energy
reach as high as 90 percent of the cross sectional
consumption as much as five times that of a belt
area. These conveyors have the ability to convey
conveyor.
horizontally, inclined or vertically, which makes
(3) Exotic auxiliary equipment and very
them extremely versatile.
costly control components have to be compared
(1) En masse type conveyors require
with the minimal roam requirements and ease of
approximately twice as much horsepower as a
installation for this type of system.
b. Advantages and disadvantages.
regular belt conveyor to move the same amount of
material the same distance. They are also very
(1) Advantages of pneumatic conveying sys-
susceptible to foreign material, which is not the
tems are that they require little maintenance, take
case with belt conveyors. Special care has to be
up less space than belt conveying equipment, are
taken when handling abrasive or corrosive
usually automatic (eliminating manual operations)
materials.
and are totally enclosed, thus avoiding
(2) En masse conveyors are advantageous
environmental fugitive emission problems, spillage
for overbunker distribution systems, offering totally
and dust.
enclosed, multiple or individual discharges which
(2) Disadvantages of pneumatic systems are
do not require complicated or extensive chutework
that they usually have a higher operating cost than
at the discharge points.
belt conveying systems because compressed air is
b. Chain. Use short pitch, drop forged alloy
used to convey the material and there is a limitation
steel, carburized or case hardened to 500-600
on the maximum size material and the amount of
Brinell Hardness Number (BHN). Each link should
fines that can be conveyed. Coal fines in excess of
be easily removable without cutting any part.
40 percent will cause pluggage problems in the
c. Trough. Provide symmetrical panels for wear
conveying pipe. Pneumatic conveying tends to
and maintenance. Sides and bottom plates will be
create additional coal fines.
5-17
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