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$4 eo ff et NOE CLOSING BULKHEAD DOORS BY ELECTRICITY After several years of costly experimentation with pneumatic and hydraulic systems for operating bulkhead doors and ar- mored hatches aboard warships, both systems have been aban- doned by the American navy in favor of an electrical system. The first electrical installations are now in working order on the Colorado and Pennsylvania, t he new 13,500-ton ar- mored cruisers. Thirteen other cruisers and _ bat- tleships now build- ing will be simi- larly equipped. The defects de- veloped in the hy- draulic and pneu- matic sy ste ms-- due mainly to the practical impossi- bility of keeping their valves and packings in work- ing order--have been overcome in the electric system, and naval authori- ties, including many who have heretofere op- posed, as necessar- ily ineffective, all power doors for bulkheads, have given the new "Long Arm" electrical system unqualified ap- proval. The bad repute into which distinctly controlled bulk- head doors fell at one time was brought about by the mem- bers of the crew who were likely to suffer from the operation of the power system. The first idea was to drop the heavy doors like so many guillotines, then followed the idea of clos- ing doors slowly by air or water pressure. But in both cases it was found that the doors could not be depended upon to shut at the right moment, nor to stay open when so required, be- cause the pneumatic and hydraulic pressure could not be per- fectly maintained. The electrical system, however, is not subject to these de- fects. It complies in every way with the specifications of the navy department providing that power doors or armor hatches "must be capable of permitting operation on the spot by power or by hand from either side of the bulkhead or deck," and "be capable of being closed by power, simultaneously from an emergency station." It is further provided that when the doors are closed and the emergency is on any door may be opened by a man at the door to allow him to pass through in performing his duties, but after he has passed through and released the controller handle the door will again close by the emergency action. The mechanism of the "Long Arm" system may be outlined as follows: (1) An emergency station, located usually in the pilot house or some convenient place above the deck. (2) The power doors or hatch-gears, supplied with three independent mechanisms. (a) The switch by which a man at any door can open and close it at will from either side. (b) The switch, operated from the emergency station, by which the door is closed upon the approach of danger. This emergency switch, although permitting absolute control, may have its operation suspended temporarily by the hand switch just mentioned. In such a case the emergency station switch HORIZONTAL DOOR LONG-ARM SYSTEM ON THE UNITED STATES ARMORED CRUISER COLORADO. Roo Ve will close the door, as soon as the hand controller is released. (c). The limit switch, by means of which the current sup- plying the motor which provides the power for closing and opening the doors, is cut off when the door has closed and locked, or has encountered an obstacle to full. closure. This switch has mechanical connection with the door or hatch-plate and is so arranged that it will cut off the current from the motor, and thus prevent blow- ing out: of the fuses. An interest- ing improvement of this part of the mechanism is one by which thre switch is made to again close the cir- cuit to the motor and thus start the door toward it s grooves after an obstruction is re- moved, e. g., when an inflow of water washes away coal Obstractin ea bunker opening. the doorand hatch gear motors are direct current, reversible, iron- clad, bi-polar, of light and compact construction for intermittent service. They are entirely en- closed in watertight cases. They are capable of carrying large ovetloads without heating or injury. The emergency station consists of two parts, one a water- tight case containing the mechanism for controlling the cir- cuit running to each door or hatch gear for closing the same, and the lamps to indicate the closure; the other case contain- ing the fuse box, in which each wire is supplied with the proper fuse. The wiring required for a complete installation of the sys- tem is very simple. It comprises one twin conductor by which the emergency station is connected with the ship's mains; one twin conductor by which the controller on each door and hatch gear is connected with the emergency station, and one twin conductor connecting the controller on each hatch gear or door with the ship's mains. Here, as in other parts of the system, great simplification has been worked by: replacing pneumatic and hydraulic power by electricity. The latter added another set of complicated machinery. to the ship's equipment, while the electric system calls for nothing more complicated than connection with the electrical mains necessary for other purposes. Lo explain the operation of the "Long Arm" system it is perhaps best to imagine an actual instance in which it would be called into play. Suppose that the Colorado is in danger of being rammed, or that her hull has been punctured by a tor- pedo. The officer of the deck or the one first aware of the danger will "press the button" of the emergency station, im- mediately releasing the gearing driven by a spring and con- trolled by an adequate escapement. This gearing then closes the circuit for operating the emergency switch in the control- ler of each door or hatch-gear. It does not start all the mo- tors at the same time, thus avoiding the necessity for a large supply of current. It starts the doors:one after the other at intervals of about three seconds, so that twenty-five doors and hatch-gears can be closed in 75 seconds from each emergency