TM 5-814-9
CHAPTER 5
OPTIONAL PREWASH
Section I. TYPES OF PREWASHES
5-1. Introduction
vehicles only. Large, offset flexors on the bottom of the tracked
vehicle lane allow maximum flexing of tracks but make it
a. The prewash is designed to remove a large amount of dirt
difficult for wheeled vehicles to traverse and maneuver. Dual-
from vehicle exteriors in the most efficient way. The prewash
purpose lanes can be used by both tracked and wheeled
should be flexible enough to handle the number and types of
vehicles. In the dual-purpose lanes, the smaller pipe flexors,
vehicles expected to use the facility. After the prewash, most
which are not offset, are easily traversed by wheeled vehicles.
vehicles will require additional washing at the wash stations so
However, the smaller flexors are not as effective as the. track
that troops can do a more detailed cleaning, reaching into
lane flexors for cleaning tracked vehicles.
crevices where a prewash might not clean. Not all vehicles will
require cleaning at a prewash. Lightly soiled and smaller
b. Configuration. Dual-purpose lanes can be used in
vehicles, such as jeeps, may proceed directly to the final wash
conjunction with tracked lanes at the same facility. Figure 5-1
stations.
shows a prewash design that uses both types of lanes. It is
recommended that no more than three lanes be combined to
b. Two types of prewash facilities have been constructed for
form one bath. Multiple baths can be linked with walls between
washing tactical vehicles: baths and spray stands. The bath is a
them. This configuration will provide maximum flexibility for
water-filled basin with water cannons mounted at each of the
the installation, since not all bath facilities will need to be filled
four corners of each lane. As vehicles are driven through the
to wash vehicles if a small group arrives. If tracked and dual-
bath, persons stationed at the water cannons spray them with
purpose lanes are combined to form one facility, the tracked
high -pressure water to remove the dirt. Spray stands emit high-
lanes should be located as close as possible to the sediment
pressure streams of water from many small nozzles directed
basin. Most of the sediment leaving the bath will be removed
toward vehicles driving through the facility. The bath is the
from the vehicles in the tracked lanes. This layout will reduce
recommended prewash, since it removes the bulk of the dirt,
the distance that wastewater with high suspended solids content
including that under the vehicle, and is the most efficient water
must travel prior to primary treatment. Figure 5-2 presents a
conservative method. The spray stand is neither as efficient nor
tracked lane in cross section. Signs may be required to direct
as effective as the bath for gross removal of soil from tactical
users to the proper type of bath lane.
vehicles.
c. Lane width. The recommended effective width of a lane
5-2. Bath prewash
is 22 feet (6.7 meters).
The bath is a water-filled basin through which vehicles drive.
Three actions in the bath operate at the same time to remove dirt
d. Bath bottom length. The length of the bath bottom is
from tracks, from wheel wells, and tank side skirts. First, the
based on the track perimeter of the largest tracked vehicle
water in the bath provides a soaking action that allows the dirt
expected to use the bath. A typical lane is 50 feet (15.2 meters)
to be more easily removed. Second, troop operated water
long from the bottom of the entrance ramp to the bottom of the
cannons placed at each corner of the bath lane spray high-
exit ramp, including the width of the trench drain opening.
pressure streams of water at the vehicles. Third, raised pipe
flexors built into the bottom of the bath flex the tracks and
e. Water level. The water level in the bath should be
wheels of the vehicles to aide in loosening embedded dirt. This,
adjustable. A range of 0 to 3.5 feet (0 to 1.10 meters) is
flexing motion is accomplished by driving the vehicle back and
recommended for maximum flexibility. Depth of water is
forth through the bath. The combination of wave action and
measured at the deepest point in the bath (fig 5-2), excluding
turbulence helps remove dirt from under skirts and wheel wells.
the depth of the trench drain. Not all vehicles can operate in a
Under light to average soiling conditions, one pass through the
3.5-foot (1. 10-meter) water level; in these cases, it must be
bath may be sufficient to remove the dirt. However, for heavier
possible to lower the water level. Depending on the types of
soiling, vehicles may require two or more forward and reverse
vehicles using the bath and the different units' requirements, an
passes over the flexors. An additional advantage of a bath
operator can regulate the level within the recommended range.
prewash over the spray stand system is that various types and
An extra 1.0 foot (30.5 centimeters) of freeboard should be
shapes of tactical vehicles can be cleaned without modifying the
added to the walls of the bath. A staff gauge or other water level
equipment. Also, the bath is more efficient at water usage than
indicator should be placed in the bath or painted on the side
is the spray stand, so treatment systems can be smaller. Finally,
wall to guide the operator when adjusting the bath depth.
the bath can more efficiently clean "skirted" vehicle types such
as the M-1 battle tank.
f. Water cannons. The bath prewash is equipped with two
stages of stand-mounted fire-fighting-type hardware with
a. Types of bath lanes. Two types of lanes have been
nozzles, each of which can deliver the required design wash
designed and developed to accommodate all type tactical
water pressure and flow to the exterior tracks or wheels of the
vehicles. Tracked vehicle lanes are designed for use by tracked
5-1
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