the supply system operators. The flow requirement is of particular
importance as it affects the reserve of the supply system established for
peak requirements, particularly for fire fighting and other emergencies.
Quality Requirements. The quality requirements for municipal and
base water supplies are well spelled out in the pertinent local health codes.
NAVFAC DM-5, Civil Engineering (Reference (1)), also has tables which show
the limits for various constituents of drinking and industrial water
supplies. Knowing these, the designer should familiarize himself with the
content of the supply he anticipates using and consider the effects of those
constituents on the facility piping, chamber, divers, and equipment to be
utilized in the chamber.
LINES. The fill and drain lines of the wet pot must be sized to handle
the water flow necessary for the missions. Water pressures used in wet pots
are usually well above the water pressure and piping strength of the local
water supply. To prevent possible damage to the local water supply by
inadvertent operation of wet pot valves, positive protection of the local
water supply must be provided, such as the backflow preventer shown in Figure
7-1. To prevent possible damage to local sewers, local regulations generally
require an air gap between a facility drain pipe and the local sewer as shown
in Figure 7-1. The fill line must have a main shutoff gate valve and a
reverse flow preventing check valve designed to withstand the intended
chamber pressures. The designer should bear in mind that as a general rule,
drawing water from a local main at a rate of not more than 8 to 10 thousand
gallons per hour will maintain overall water clarity while water velocities
for greater flow rates will always dislodge rust deposits and debris in the
mains. Removal of rust and debris may require the water to be circulated
through the filter for hours.
CIRCULATION. It is necessary to circulate the water through filters to
control bacteria-algae growth and maintain clarity. Experience has shown
that the circulation loop should have sufficient capacity for a complete
change of water every 5 to 8 hours.
DRAIN. The wet pot should drain by gravity with no gas pressure in the
chamber. A pump may be required to assist drainage to elevated sewers.
Provisions should be made for draining under gas pressure in an emergency.
Under some types of use, the water may be considered polluted and the
ecological impact of draining directly into a sewer or storm drain must be
considered. NAVFAC DM-5 Civil Engineering, (Reference (1)), provides
information on sanitary system requirements.
Sanitary Drain. Discharge into a sanitary system may overload the
lines and treatment system. The authority responsible for operating the
sanitary system should be contacted.
If a sanitary system is utilized, the designer
must specify reverse flow prevention valves on
all adjacent connecting lines which may be affected
by an overload. Situations are on record wherein