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30.7.2.1
Unless the requirements of 30.7.2.2 are met, a pressure tank shall be provided. The pressure tank shall be sized and constructed so that the following occurs:
  1. The tank shall contain a standing charge of freshwater equal to that specified by Table 30.7.2.1.
  2. The pressure tank shall be sized in accordance with 5.2.4.
  3. A glass gauge shall be provided to indicate the correct level of water within the pressure tank.
  4. Arrangements shall be provided for maintaining an air pressure in the tank such that, while the standing charge of water is being expended, the pressure will not be less than that necessary to provide the design pressure and flow of the hydraulically most remote design area.
  5. Suitable means of replenishing the air under pressure and the freshwater standing charge in the tank shall be provided.
  6. Tank construction shall be in accordance with the applicable requirements of 46 CFR, Subchapter F, "Marine Engineering."
Table 30.7.2.1 Required Water Supply
System Type Additional Water Volume
Wet pipe system
Flow requirement of the hydraulically most remote system demand for 1 minute
Preaction system
Deluge
system
Dry pipe
system
Flow requirement of the hydraulically most remote system demand for 1 minute of system demand plus the volume needed to fill all dry piping
30.7.2.2 Pressure Tank Alternative
In lieu of a pressure tank, a dedicated pump connected to a freshwater tank shall be permitted to be used, provided the following conditions are met:
  1. The pump is listed for marine use and is sized to meet the required system demand.
  2. The suction for the fire pump is located below the suction for the freshwater system so that there shall be a minimum water supply of at least 1 minute for the required system demand.
  3. Pressure switches are provided in the system and the controller for the pump that automatically start the pump within 10 seconds after detection of a pressure drop of more than 5 percent.
  4. There shall be a reduced pressure zone backflow preventer to prevent contamination of the potable water system by saltwater.
  5. This pump has at least two sources of power. Where the sources of power are electrical, these shall be a main generator and an emergency source of power. One supply shall be taken from the main switchboard, by separate feeder reserved solely for that purpose. This feeder shall be run to an automatic changeover switch situated near the sprinkler unit, and the switch shall normally be kept closed to the feeder from the emergency switchboard. The changeover switch shall be clearly labeled, and no other switch shall be permitted in these feeders.
30.7.2.3 Relief Valves
30.7.2.3.1
Relief valves shall be installed on the tank to avoid overpressurization and false actuation of any dry pipe valve.
30.7.2.3.2
Relief valves shall comply with 46 CFR 54.15-10.
30.7.2.4 Power Source
30.7.2.4.1
There shall be not less than two sources of power for the compressors that supply air to the pressure tank.
30.7.2.4.2
Where the sources of power are electrical, these shall be a main generator and an emergency source of power.
30.7.2.4.3
One supply shall be taken from the main switchboard, by separate feeders reserved solely for that purpose.
30.7.2.4.4
Such feeders shall be run to a changeover switch situated near the air compressor, and the switch normally shall be kept closed to the feeder from the emergency switchboard.
30.7.2.4.5
The changeover switch shall be clearly labeled, and no other switch shall be permitted in these feeders.
30.7.2.5 Multiple Tanks
30.7.2.5.1
More than one pressure tank can be installed, provided that each is treated as a single water source when determining valve arrangements.
30.7.2.5.2
Check valves shall be installed to prohibit flow from tank to tank or from pump to tank, unless the tank is designed to hold only pressurized air.
30.7.2.6
In systems subject to use with saltwater, valves shall be so arranged as to prohibit contamination of the pressure tank with saltwater.
30.7.2.7*
Where applicable, a means shall be provided to restrict the amount of air that can enter the pressure tank from the air supply system. A means shall also be provided to prevent water from backflowing into the air supply system.

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