b. Two plug- or ball-type suction valves
c. Two plug- or ball-type discharge valves
Each CHT tank has two nonclog marine sewage
pumps connected in parallel. The pumps may
d. Two pump discharge check valves with a
discharge sewage to a tender, barge, shore facility,
or directly overboard, depending on the position of
the discharge pump diverter valve. Each pump has
e. A duplex pump controller
a full-port, plug-, or ball-type suction and discharge
valve and a discharge swing-check valve with a
f. A high-level alarm
hold-open device. See NSTM, chapter 503, for an
explanation of sewage pumps.
g. Liquid-level sensors
TYPES OF CHT SYSTEMS
3. Comminutor: There is one in each soil
drain or combined soil and waste drain entering
There are two types of CHT systems, depending
on the capacity of the holding tank. Systems with a
tank capacity greater than 2,000 gallons use a
4. Aeration supply and diffusers.
comminutor (com-MIN-u-tor). A comminutor
chops, chews up, and grinds fragments, and softens
5. Firemain flushing connections and washdown
thick material into a semifluid consistency. Systems
nozzle for spray cleaning the interior of the tank.
with a tank capacity of less than 2,000 gallons use
6. Piping, valves, and fittings.
C O M M I N U T O R S U B S Y S T E M . --The
In comminutor-type systems, the comminutor,
comminutors are installed in the soil drain lines.
located in the soil drain or in the combined soil and
They may be installed in any position as long as
waste drain, macerates (chews up) solids passing
gravity flow can take place. However, a 20-inch
into the CHT tank. If the comminutor jams or
clearance is required on the belt side to allow for
plugs, a bypass line provides drainage around the
the removal and repair of the cutter assembly.
comminutor into the tank. If a valve is fitted in the
bypass line, it must always remain open during
The cutter assembly breaks up solids into
routine operation of the system. Isolationvalves are
smaller particles. Be sure that no metal objects go
fitted directly before and after the comminutor to
down the drains. Any metal over 0.010 inch thick
allow for maintenance. Also, most installations have
can damage the cutter blades.
an access opening for removing foreign objects that
may jam or plug the comminutor.
The comminutor is electrically operated. The
shafts operate at different individual speeds for
The major components of the comminutor-type
more effective breaking up of solids and for
CHT system are discussed in the following
paragraphs and shown in figure 17-1 (at the
end of this chapter).
The comminutor does not have to be removed
for scheduled planned maintenance. If the cutter
1. CHT tank: Each tank will have a capacity of
assembly is to be removed, it should first be either
2,000 gallons or more.
hosed down or steam-cleaned.
sanitation procedures listed earlier under the
2. CHT pump set: There is one set per tank;
Sanitation heading.) The assembly can then be
a pump set consists of the following components:
removed by using extreme care. The inside
diameter of the housing is a sealing surface, and
a . Two motor-driven (mixed flow)
damage to it could cause leakage.