TM 5-814-9
freezing weather will require special design con-
The maximum number of vehicles that
siderations to protect wash components, pumps and
must be washed at the facility in a time
piping. Most of the wash components, particularly
specified by the installation (peak wash
the prewash, may not be feasible to operate near
period) and the expected process rate
freezing conditions because of the safety hazard
through the facility. Equations 3-2 and 3-3
caused by overspray freezing on the pavement.
will help the designer determine the
Enclosed facilities may be warranted, however, they
number of each type of lane needed for the
are very expensive from both a capital and
prewash system. The installation's
operations standpoint. Another climatic consider-
requirements will dictate how the result
ation in the design is the evaporation rate in the
should be treated. If the maximum washing
region. In an area with high evaporative losses and
time is critical, the number should be
low rainfall, certain features of the CVWF may not
rounded up; otherwise, the number of lanes
be practical. For example, a spray stand creates
should be rounded to the nearest whole
large water losses due to overspray. Use of any
number.
prewash system increases the volume required in
the treatment system; with the higher water volume,
No. tracked
Max. no. tracked vehicles to be washed
=
the surface area of the basins must be increased
lanes
(Process rate x peak washing period)
(particularly a lagoon treatment), which promotes
(eq 3-2)
evaporative losses even more. The designer must
evaluate the potential evaporative loss as it affects
In equation 3-3, only the tracked and wheeled vehicles ex-
the need for make-up water and weigh this against
pected to use the dual-purpose lane should be considered in
the benefits of either a recycle system or a discharge
the equation. The number of tracked vehicles using the
system.
tracked vehicle lane should not be included, since they will
not be washed twice in the prewash.
b. Prewash. A prewash is used to reduce the time needed
to wash vehicles, since it removes the bulk of the dirt in a
timely, efficient way. Its function is to reduce the amount of
time each vehicle must spend at the wash stations.
Bath prewash. A bath prewash is currently the
(c)
(1)
An example will better explain how to use the
most efficient and effective method to remove dirt
equations. Consider an installation that needs
from the exteriors of tactical vehicles. A large
to wash 42 heavy tracked vehicles, 88 light
volume of water is required to fill the bath, but
tracked vehicles, and 125 wheeled vehicles in
because of the reduced wash time required, the
the prewash during peak use. The installation
overall water volume required for cleaning a
requires that all of the vehicles be washed in
large number of vehicles may be reduced. Lanes
9 hours. Soils at the installation are extremely
specifically designed for washing tracked
cohesive clays, so the process rates through
vehicles can be provided; lanes which can
the prewash are expected to be slow. The
accommodate both tracked and wheeled vehicles
designer had determined that the soiling index
(referred to as dual purpose lanes) can also be
(Si) is 8 and from the chart (fig 3-4 estimates
provided. These are described further in chapter
that five heavy tracked vehicles per hour can
5. Wheeled vehicles under 2.5 tons would not
be washed in each lane; seven light tracked
normally use the prewash bath.
vehicles per hour per lane can be washed; and
eleven wheeled vehicles per hour per lane can
(a)
Process Rate. In a tracked bath lane, six to
be washed in a dual-purpose lane. For initial
ten tracked vehicles per hour can be
calculations the following will be used.
washed. In a dual-purpose lane, ten to
42 heavy tracked
88 light tracked
0.93 1.40
fifteen wheeled vehicles per hour can be
5 veh/hr/lane x 9 hr
7 veh/hr/lane x 9 hr
washed. The amount of soiling will
determine the actual number of vehicles
= 2.33 tracked lanes
that can be processed through the facility;
125 wheeled vehicles
1.26 dualpurpose
the heavier the soiling, the slower the
11 veh/hr/lane x 9 hr
vehicles can be processed. By using the
Soiling Index (Si) in conjunction with the
The designer realizes that, with three tracked vehicle lanes and
processing rate chart shown on figure 3-4,
one dual-purpose lane, the tracked vehicles will be washed in
the throughput rate can be determined for a
less than 9 hours, but the wheeled vehicles will require more
particular design.
than 9 hours. To achieve a more even distribution of vehicle
washing, the designer recalculates the number of lanes needed
(b)
Number of lanes. The number of lanes for
by assuming that some of the light tracked vehicles will use the
the prewash will depend on two factors:
dual-purpose lanes. The designer adjusts the process rate for the
3-6
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