have passed through steam traps. All of the other drains
CONTAMINATED DRAINAGE SYSTEM.--A
are in the form of water after they have passed through
contaminated drainage system is installed in each main
and auxiliary machinery space where dry bilges must
steam traps.
be maintained. The contaminated drainage system
HIGH-PRESSURE STEAM DRAINAGE
collects oil and water from machinery and piping that
SYSTEM.-- High-pressure drains generally include
normally have some leakage, and drainage from any
drains from superheater headers, throttle valves, main
other services that may at times be contaminated. The
and auxiliary steam lines, steam catapults (on carriers),
contaminated drains are collected in a bilge sump tank
and other steam equipment or systems that operate at
located in the same machinery space. The contents of
150 psi or above. High-pressure drains are returned to
the bilge sump tank do not go to the feed system;
the feed system by way of the DFT.
SERVICE STEAM DRAINAGE
On recently constructed ships, drains that contain
SYSTEM.-- The service steam drainage system
collects drains from low-pressure (below 150 psi)
oily water drain systems. Separating the drains permits
steam piping systems and steam equipment outside of
the machinery spaces. Space heaters and equipment
used in the laundry, the tailor shop, the galley, and the
Freshwater Systems
pantry are typical sources of drains for the service steam
drainage system. On some ships, these drains discharge
Practically all fresh water used aboard ship is made
into the most convenient freshwater drain collecting
tank. On other ships, particularly on large combatant
the resulting vapor. Fresh potable water is stored in
ships such as carriers, the service steam drains
potable water tanks at a distance from the machinery
discharge to two special steam drain collecting tanks
spaces. The water intended for boiler use is stored in
located in the machinery spaces. One is in a forward
feed tanks located in the double bottoms or in wing
machinery space, while the other one is in an after
tanks adjacent to the machinery spaces. The potable
machinery space. The drains are then returned from
water system supplies hot and cold potable water to
the service steam drain collecting tanks to the feed
scuttlebutts, sinks, showers, scullery, sick bay, and the
system.
galley. The normal operating pressure is approximately
35 psi. In some ships, water pressure is maintained by
automatic electric pumps that take suction on the ship's
only clean drains that are suitable for use as boiler feed.
potable water storage tanks. Constant pressure is
Contaminated service steam drains (such as those from
maintained by admitting compressed air to the pressure
laundry presses) are discharged as authorized.
tank. When there is a decline in tank pressure, the pump
FRESHWATER DRAIN COLLECTING
SYSTEM.-- The freshwater drain collecting system
pumps discharge directly to the distribution system.
(sometimes called the low-pressure drain system)
The pressure in the system is provided by the
collects drainage from various piping systems,
continuous operation of a motor-driven centrifugal
machinery, and equipment that operate at steam
water pump taking suction from the ship's tanks. When
pressures of less than 150 psi. As we have seen, both
potable water is supplied to other systems, the supply
the service steam drainage system and the oil heating
to the nonpotable system is through an air gap. There
drainage system can discharge to the freshwater drain
should not be any direct cross connection between the
collecting tank. However, they normally discharge
potable water system and any other system. An air gap
more directly to the condensate of the feed system. In
in a water supply system is the unobstructed vertical
general, the freshwater drain collecting system collects
distance through free atmosphere between the lowest
gravity drains, turbine gland seal drains, auxiliary
opening from any pipe or faucet supplying water to a
tank or plumbing fixture and the flood-level rim of the
variety of other low-pressure drains that result from the
tank or plumbing fixture. Each hose connection in the
machinery and piping. Freshwater drains are collected
breaker backflow preventer on the downstream side of
in freshwater drain collecting tanks that are located in
the hose control valve.
the machinery spaces. The contents of these tanks are
Some ships use instantaneous coil-type heaters in
discharged to the feed system.
the hot water system. Other ships are of the circulating
15-42