3. The Air Chamber.
This contains the motive power of the torpedo and it comes just behind the explosive chamber. The air is compressed into the compartment by means of air-compressing pumps fitted on board ship, and the latest types are tested to a pressure of 1,700 lbs. to the square inch.
4. The Balance Chamber.
Next the air chamber comes the balance, or secret chamber, although the secret is now universally known. Here is contained the mechanism for automatically transmitting to the horizontal rudders the movements necessary for keeping the torpedo at a uniform and pre-arranged depth below the surface during its run. It consists of a hydrostatic valve and a pendulum whose combined movements are transmitted to an air cylinder called a “servo-motor,” placed in the engine room. The hydrostatic valve is kept in its place by a spring that is forced in by the pressure of the water when the torpedo goes below a certain depth to which the valve has previously been adjusted. If the pressure be less than that of the set depth the opposite action takes place. This valve is connected with the servo-motor, which in its turn acts on the horizontal rudders. The pendulum consists of a heavy iron weight curved to correspond with the circular section of the torpedo and suspended by the pivoted steel rods or arms. It swings in a fore and aft direction and is connected by rods to the rudder for a certain distance after the discharge of the torpedo. A controlling gear is provided which keeps the rudders fixed. It will thus be seen that by the combined actions of the hydrostatic valve and the pendulum the Whitehead, after leaving the tube, is brought to the proper depth very rapidly and is held at this depth throughout her run. Both these devices are necessary, as the torpedo has a great tendency to run down an inclined plane at great speed, and this requires to be checked. In addition the balance chamber contains various valves (the stop valve, the charging valve, the starting valve, the delay action valve and the reducing valve) through which the air passes on its way to the engines from the air chamber.
5. The Engine Room.
Inside the engine room are the propelling engines and the servo-motor. The engines are of the single-acting three-cylinder Brotherhood type. The compressed air, after leaving the air reservoir, passes through the main pipe to the pressure-reducing valve. In the latest pattern 18 inch Whitehead the indicated horse power is 56. The torpedo is started by means of a trigger which projects a little beyond the casing of the torpedo, and which automatically opens the starting valve when the torpedo is fired, the trigger just before leaving the tube is caught by a catch in the tube which draws it back when the catch releases itself.
The Servo-Motor.
This ingenious apparatus was called into existence owing to the fact that the mechanism of the balance chamber was unable, through its feeble power, to work the horizontal rudders of the faster Whiteheads direct. The servo-motor is, then, the air engine from which is derived the power to move the diving rudders. It is only about 4 inches long, but so great is its power that with only half-an-ounce pressure on the slide valve the piston is capable of lifting 180 lbs. It consists of a cylinder, a piston, and a cylindrical slide valve. Its balance mechanism acts on the slide valve of the servo-motor, and this acts on the piston, and the motion of the piston is transmitted to the diving rudders by means of a rod and a system of levers.
6. The Buoyancy Chamber.
Abaft the engine room is the buoyancy chamber which gives the necessary buoyancy to the torpedo: to guard against the collapse of the chamber flat steel rings are fitted into it for support. In the “Tail,” the rearmost compartments of the torpedo, are carried the bevel wheel mechanism, the vertical and horizontal rudders and the propellers, and the counter mechanism for adjusting the length of run.