BM-4 Terror Pneumatics
The leading feature of interest in the Terror, an Amphitrite class monitor, was the lately introduced compressed-air system for steering the ship and loading and handling her guns, an innovation which has been received with much commendation. Steam-power and hydraulic power had previously been employed for these purposes, but the new agent appeared to have elements of superiority over both its competitors. One of its main advantages has to do with ventilation. Steam and hydraulic engines exhaust outwardly, by means of pipes passing through the hull of the ship, but the pneumatic or compressed-air engine may be made to exhaust either into the outer air or into the ship.
The flow of air from the exhaust pipes of a pneumatic engine would be of the greatest service as a means of ventilation in some confined portions of a ship's interior, as in the close and contracted steering-room, situated far aft below the protective deck, or in the interior of the turret, with its heat-yielding machinery and its crowd of men during a battle. Localities which would be uncomfortably hot if provided with steam piping, and also exposed to danger from the possibility of a steam-pipe breaking during action, could with pneumatic power avoid these difficulties and be supplied with air of reduced and even temperature.
With his eye at the telescope and his hand upon the levers which control all the apparatus below, the officer needs but to bring the cross hairs on the object-glass of the telescope to cover the target, when, by a slight pressure of an electric button, he can hurl a 500-pound shell from the muzzle of the great cannon with the nicest precision upon the distant mark.
The recoil of the gun is easily controlled by the same system of compressed air. Beside it are two pneumatic cylinders, within which act pistons attached to the gun, and held in position by an air-pressure of about five hundred pounds to the square inch. As the piston is driven back into the cylinder by the recoil of the gun, the air, compressed into a smaller space, rapidly increases in pressure. Too great pressure is prevented by an arrangement for letting a portion of the air escape through the piston to the opposite side, while sufficient pressure remains at the end of the recoil to force the gun back to its place. The elasticity of the air prevents all shock, it forming an easy cushion both for the recoil and the return movement of the gun.
These are not the only services performed by the useful air engines. That alluded to of lifting the ammunition and loading the gun is of sufficient interest and importance to be described. Immediately below the tunnel lies a room of great importance in the economy of the ship, the handling room, in which during an engagement a crew is kept actively engaged in supplying food for the rapacious engines of destruction above. Adjoining this room, and opening into it by water-tight doors, are the magazine and shell-rooms, the doors of which are usually kept tightly closed.
In the centre of the landing-room is a pneumatic loading machine, which rotates upon a vertical shaft and can be swung to right or left for the reception of the load. This consists of the 500-pound shell and the cartridge, the latter being made up in two sections. These are brought from their respective rooms on an overhead trolley, placed successively in the loading machine, and transferred from this to the pockets of the loading car. There are three of these pockets, one for the reception of each of the three portions of the charge. The car is now lifted into the turret, and is brought to a stop with the shell directly opposite the open breech of the gun.
All these movements are performed readily and quickly by aid of compressed air, and the same useful servant completes the work, driving the shell into the gun by the thrust of a pneumatic rammer, and after it the two sections of the cartridge, the cage being rotated to bring each of them into position. The breech-plug is then swung into place, thrust into the open breech, and firmly locked. All these operations are performed quickly and almost automatically, and shell after shell can be discharged with rapidity from each of the two great guns.
The steering is the final operation performed by the pneumatic apparatus, and may be briefly described. The tiller by which the rudder is moved rests between two long cylinders whose pistons are connected by a common rod, in whose centre is a hollow cross-head in which the tiller has free room to slide. Compressed air is admitted to one cylinder and exhausted from the other, driving the pistons and the rod forward or backward as the helm is to be shifted to port or to starboard. When the tiller is at rest, air lies behind each piston, and forms a useful elastic cushion to take up the shocks of the tiller as it is violently moved in rough weather, and save the framework of the ship from the strain of these shocks.
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