ENGINEMAN 1 & C
3. The comminutor. One comminutor is
located in each soil drain or combined drain enter-
ing each tank.
set up to collect and hold the discharges from soil
4. The aeration supply system.
5. The firemain flushing connections and
spray cleaning nozzle for tank washdown.
6. The piping, valves, and fittings.
2. In Port. During in-port periods, the CHT
system collects, holds, and transfers to shore
sewage facility all discharges from soil and waste
3. At Sea. When operating at sea outside
restricted areas, the CHT system is set up to divert
discharges from both soil and waste drains
The strainer-type system incorporates an
overflow strainer within the CHT tank and an in-
flow strainer mounted on the discharge side of
each pump. The drain collection piping directs
sewage flow through the overflow strainer where
liquids may overflow into the CHT tank if the
inflow strainer or the pumps become clogged.
Solid and liquid wastes flow through the ball or
plug valve and the check valves until they reach
the pump discharge piping. At this junction, the
sewage flow passes through the inflow strainer
where large solids are collected, then through the
pumps, and back into the CHT tank. The inflow
strainer limits the flow of solids, but liquids are
allowed to pass through the pump into the tank.
Each time the pump operates, its inflow strainer
is cleaned by the reverse flow of liquid being
pumped from the tank. The strainer-type system
components, shown in figure 8-6, include:
While transiting a restricted zone, soil drains are
routed to the CHT tanks and the waste drains are
diverted overboard. Both CHT pump controller
switches are in the OFF position. Pump suction
valves A and inflow stop valve G (for strainer
system only). are open (see figure 8-6). Pump
discharge valves B and the tank washdown
supply valve are closed. Soil drain diverter valves
H are in the CHT COLLECTION position. Waste
drain diverter valves J are in the OVERBOARD
position, discharging through the gag scupper
1. The CHT tank. The capacity of each tank
usually is less than 2000 gallons.
2. The CHT pump set; one pump set per tank.
A pump set consists of two motor-driven pumps,
two suction plug or ball valves, two discharge plug
or ball valves, two discharge check valves (with
hold-open device), a pump controller, a high level
alarm, and an appropriate number of liquid level
For systems equipped with a comminutor (see
figure 8-5) and an aeration system (see figure 8-7),
open the comminutor isolation valves, D and
operate the comminutor. The tank contents must
be aerated continuously. Operate the air blower
and open discharge valve M (shown in figure 8-7).
Air also can be supplied by opening the ship serv-
ice air supply valve N (also shown in figure 8-7).
If an aspirator system is employed, the aspirator
pump should be activated.
3. The Firemain flushing connections and
spray cleaning nozzle for tank washdowns.
4. The piping, valves, and fittings.
CHT OPERATIONAL MODES
Whenever a high level alarm sounds,
immediate action must be taken to close
the isolation valves on drains below the
overboard discharge and to divert upper
level drains overboard to preclude flooding
The CHT system can be used in any of three
district modes of operation in accordance with any
one of the following situations:
1. Transiting Restricted Zones. When tran-
siting restricted zones, the CHT system must be
After sewage transfer hose connections are
completed, both soil and waste drains are routed
to the CHT tank and then discharged to a shore
receiving facility, nested ship, or barge receiving
station. When connecting the sewage transfer
hose, proper chafing gear and supporting lines