In vessels with a large number of watertight bulkhead plates and access doors located below the waterline, a powered operating system is essential. Various systems are employed, primarily electrical and hydraulic types. A circuit diagram for a hydraulically operated system is commonly provided.

Hydraulic System Operation:

• At each door, a motor-driven pump supplies oil at a pressure of 48 bar to a double-acting cylinder via a control valve.
• This valve is actuated electrically by solenoids when operating from bridge control.

Local Control:

• A local control station is positioned adjacent to each door, allowing for shut, open, or intermediate positions.
• The manual control lever, operable from either side of the bulkhead, actuates a pilot valve that controls the pump motor circuit under all modes of control.
• The system utilizes the area differential of the piston to provide a slightly greater force when opening the door.
• The control lever is spring-loaded to the mid-position, ensuring a hydraulic lock within the cylinder. This prevents unintended movement of the door due to ship motion.

Bridge Control:

• The bridge controller is designed to close up to 20 doors in sequence within 60 seconds.
• This 60-second period includes a 10-second audible alarm at each door before closing begins. The alarm continues until the door is fully shut.
• The “Close” and “Re-open” commands from the bridge energize the solenoids in the door’s control valve to activate the pump motor.
• Limit switches, triggered by door movement, regulate the electrical circuit.
• If any door is re-opened locally while under a "close" command from the bridge, it will automatically re-close when the local control lever is released.

Emergency Control:

• In situations where no electrical power is available, the door can still be operated by manually using a hand pump and control valves at either the local or remote stations.

Light Indication System:

• A colored light indicator on the bridge displays the status of each door:
  • Green – Door shut
  • Red – Door open
  Part (b)

  Source of Power for Closure, Alarm, and Indicator

  • The DC power supply for the pump is normally obtained from a DC/AC transformer rectifier unit, which is common to all doors in the system.
  • In emergency conditions, the power supply is sourced from the ship’s batteries.
  • To ensure continuous power availability, all indicator lights and audible alarms are connected to both the DC supply and the ship’s batteries.