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 set up to collect and hold the discharges from soil drains only.

2. In Port. During in-port periods, the CHT system collects, holds, and transfers to shore sewage facility all discharges from soil and waste drains.

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 overboard.

Transmit Mode

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 valves.

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.

WARNING

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 of spaces.

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

Figure 8-6.Strainer-type CHT system.

should be fitted where required to protect the hose. Care should be taken to prevent the hose from snagging between the ship and the pier. Valves A, B, and C should be lined up and set for discharge to the shore side deck discharge at valve F. The receiving station sewer valve should then be opened, followed by valve F at the deck connection. With a person stationed at deck connection F, pass the word to the CHT pump room that hose connections have been made (see figures 8-5 and 8-6).

Set both pump controller selector switches to AUTO position. Set soil drain diverter valves H and waste drain diverter valves J to the CHT COLLECTION position for drainage to the CHT tank. After the tank is pumped down and the

Figure 8-7.Aeration subsystem.

pump stops, open the tank washdown supply valve and wash the tank for 30 minutes. Close the tank washdown supply valve.

The comminutor and aeration system should be operated continuously in the in-port mode. During extended in-port transfer operations, the CHT tank must be washed a minimum of 30 min/wk. While discharging waste through transfer hoses, check periodically for leakage, kinking, and snagging.

In the event of a high level alarm, the operator should recognize that a problem exists with the pumps, the discharge piping, or both. If the tank completely fills while the system malfunction is being investigated, the waste will overflow over-board and through any heads or fixtures located below the overflow discharge lines. Drain lines from these fixtures incorporate both a check valve and an isolation, or cutoff, valve. These fixtures must be identified prior to initial system use. Whenever a high level alarm sounds, immediate action must be taken to close the isolation valves on drains located below the CHT tank overflow line discharge and divert upper deck drains over-board to preclude flooding of space. In the event of leakage or snagging of the transfer hoses, close valve F (shown in figures 8-5 and 8-6) at the deck connection only (closure of pier valve may cause the discharge hose to rupture). Line up pump discharge diverter valve C for overboard discharge, to prevent overflow or backup of drains located below the tank overflow.