156

NIOHOLLS'S SEAMANSHIP AND NAUTICAL KNOWLEDGE

signal bell is given at each door, then all doors connected to the system
are closed by means of hydraulic rams; and, on the doors reaching their
closed positions, glass discs are illuminated in the electrical indicator
mounted over the control, thus indicating that the operation has been
effected. By reversing the control valve handwheel the doors may be
opened again. Each door when closed may be opened by any person
wishing to pass through by merely pressing a lever, but immediately
the lever is released the door automatically closes again.

MAIH5 KOUMO SmP^.

TYPICAL ARRANGEMENT OF
HORIZONTAL SLIDING "STONE" WATERTIGHT DOOR.
- Fig. 21.
An identification disc is provided for each door showing by
its illumination on the indicator in the whee}house whether it is closed
or open and its particular position in the ship.
The above figure snows a typical arrangement of a horizontal
sliding watertight door. The pumping machinery to maintain a con-
stant pressure of water to operate the hydraulic rams is installed in
the engine-room.