The Compressed Air Tanks.—The air pressure chamber is simply a large steel tank and air is pumped into it until it is under a pressure of about 2,000 pounds to the square inch; this means that for every square inch of the surface of the tank there is a force pressing against it of about one ton.
The air is let out of the tank through what is known as a reducing valve, which is in turn connected to the engines, and more about it will be said a little later. A reducing valve is simply a valve that regulates the amount of air which flows from the tank into the engine and keeps it at the same pressure all the time.
If the valve were not used, the air in the tank, which is at first under 2,000 pounds pressure, would drive the torpedo forward at a tremendous rate of speed at first, but as the air from the tank was used up by the engine it would lose pressure and the torpedo would soon stop altogether. But when a reducing valve is used the torpedo keeps up its same high speed until it has run its course and has either hit the ship or missed it.
What Is in the Balance Chamber.—In the balance chamber is the mechanism that controls the steering and the diving rudders, and it is these that keep the torpedo on a straight course and at the right depth under the water.
The controlling mechanism is formed of four chief devices, which are (1) a gyroscope (pronounced ji´-ro-skop); (2) a compressed air motor, which drives the gyroscope; (3) a water pressure control; and (4) a pendulum control.
The Automatic Gyro Control.—The gyroscope, or just gyro, as it is called for short, is a kind of spinning top and you can buy a toy one for a quarter.[22] It is simply a heavy wheel fixed to a shaft, or spindle, and this is pivoted in a ring, as shown at A in [Fig. 39].
Now hold the gyro as shown at B and give the wheel a good spin. This done, walk straight ahead, and as long as you do so you will hardly know that you are carrying the gyro, but the moment you try to change your direction you will feel the gyro twisting in your hand to counteract the movement.
This is the purpose of the gyro in a torpedo, but in this case the wheel is very heavy and it is revolved at a high speed by a compressed air motor. The gyro is set with its shaft at right angles with the long axis of the torpedo, as shown at C.