Section II. BATH PREWASH SUPPORT FACILITIES
5-4. Wash water supply lines
5-6. Bypass lane
Wash water supply lines transport water under pressure, from
A bypass lane is provided to allow lightly soiled vehicles to
the source to the washing structures. Supply piping shall be
bypass the prewash and advance to the wash stations. Expe-
ductile iron, steel or other material resistant to damage from
rience has shown that wheeled vehicles bypass the prewash
water hammer. Plastic pipe is not acceptable for use in the
most often. The recommended lane width is 22 feet (6.7
supply piping. Frequently operated underground valves shall be
meters). The bypass lane must have positive drainage to prevent
accessible via manholes or valve boxes. In regions that have
the buildup of water and sediment. When a prewash is provided,
freezing temperatures, the system must be self-draining to
a bypass lane around the wash stations must also be provided.
prevent freezing. Adequate valving should be incorporated to
This enables the vehicles leaving the prewash which do not
allow for isolation of individual wash stations or wash positions.
require additional washing to bypass the wash stations and
advance to the final assembly area.
5-5. Wastewater conveyances
The wastewater conveyances from the washing structure to the
treatment system should be open trenches with a slope sufficient
Adequate lighting should be provided if nighttime washing
to produce 5 fps (1.8 meters per second) velocity. The
operations are required by the installation. For worker safety,
conveyances to the treatment system shall be as straight as
overhead lighting must also be installed in the areas of vehicle
possible; limiting the number of turns will minimize solids
movement. Work-level lighting must be provided at the bath
deposition which can build up and block the pipes and trench
prewash so that users can see the vehicle areas to be cleaned.
drains. If closed conduit is used due to site constraints, such as
Lighting intensities of 3 foot-candles from most lights measured
the need to pass under a road, manholes must be provided at
at ground level and 5 foot-candles from horizontal projecting
each change in pipe direction and slope and at each pipe
work-level lights measured at the vehicle sides should be
intersection (see chap 6).
maintained in the washing area. All areas of adjacent hardstand
such as assembly/staging and travel lanes should have a
minimum lighting intensity of one foot-candle.