PRINCIPLES OF PNEUMATICS
PNEUMATICS is that branch of mechanics that deals with the mechanical properties of gases. Perhaps the most common application of these properties in the Navy today is the use of compressed air. Compressed air is used to transmit pressure in a variety of applications. For example, in tires and air-cushioned springs, compressed air acts as a cushion to absorb shock. Air brakes on locomotives and large trucks contribute greatly to the safety of railroad and truck transportation. In the Navy, compressed air is used in many ways, For example, tools such as riveting hammers and pneumatic drills are air operated. Automatic combustion control systems use compressed air for the operation of the instruments. Compressed air is also used in diving bells and diving suits. Our following discussion on the use of compressed air as an aid in the control of submarines will help you understand the theory of pneumatics.
Submarines are designed with a number of tanks that may be used for the control of the ship. These tanks are flooded with water to submerge, or they are filled with compressed air to surface.
The compressed air for the pneumatic system is maintained in storage tanks (called banks) at a pressure of 4500 psi. During surfacing, the pneumatic system delivers compressed air to the desired control tanks (the tanks filled with water). Since the pressure of the air is greater than the pressure of the water, the water is forced out of the tank. As a result, the weight of the ship decreases. It becomes more buoyant and rises to the surface.
As you look around, you see not only that your ship is constructed of metal, but also that the boilers, piping system, machinery, and even your bunk and locker are constructed of some type of metal. No one type of metal can serve all the needs aboard ship. Many types of metals or metal alloys must be used. A strong metal must be used for some parts of a ship, while a lightweight metal is needed for other parts. Some areas require special metal that can be shaped or worked very easily.
The physical properties of some metals or metal alloys make them more suitable for one use than for another. Various terms are used in describing the physical properties of metals. By studying the following explanations of these terms, you should have a better understanding of why certain metals are used on one part of the ship's structure and not on another part.
DUCTILITY refers to the ability of a metal to stretch or bend without breaking. Soft iron, soft steel, and copper are ductile metals.
HARDNESS refers to the ability of a metal to resist penetration, wear, or cutting action.
STRENGTH refers to the ability of a metal to maintain heavy loads (or force) without breaking. Steel, for example, is strong, but lead is weak.
TOUGHNESS is the property of a metal that will not permit it to tear or shear (cut) easily and will allow it to stretch without breaking.
Metal preservation aboard ship is a continuous operation, since the metals are constantly exposed to fumes, water, acids, and moist salt air. All of these elements will eventually cause corrosion. The corrosion of iron and steel is called rusting. This results in the formation of iron oxide (iron and oxygen) on the surface of the metal. Iron oxide (or rust) can be identified easily by its reddish color. (A blackish hue occurs in the first stage of rusting but is seldom thought of as rust.) Corrosion can be reduced or prevented by use of better grades of alloyed metals. Chromium and nickel are commonly used. Coating the surface with paint or other metal preservatives also helps prevent rust.
Metals and alloys are divided into two general classes: ferrous and nonferrous. Ferrous metals are those composed primarily of iron. Nonferrous metals are those composed primarily of some element or elements other than iron. One way to tell a common ferrous metal from a nonferrous metal is by using a magnet. Most ferrous metal is magnetic, and nonferrous metal is nonmagnetic.
Elements must be alloyed (or mixed) together to obtain the desired physical properties of a metal. For example, alloying (or mixing) chromium and nickel with iron produces a metal known as special treatment steel (STS). An STS has great resistance to penetrating and shearing forces. A nonferrous alloy that has many uses aboard ship is copper-nickel. It is used extensively in saltwater piping systems. Copper-nickel is a mixture of copper and nickel. Many other different metals and alloys are used aboard ship that will not be discussed here.
With all the different types of metals used aboard ship, some way must be used to identify these metals in the storeroom. The Navy uses two systems to identify metals: the continuous identification marking system and the color marking system. These systems have been designed so even after a portion of the metal has been removed, the identifying marks are still visible.
In the continuous identification marking system, the identifying information is actually painted on the metal with a heavy ink. This marking appears at specified intervals over the length of the metal. The marking contains the producer's trademark and the commercial designation of the metal. The marking also indicates the physical condition of the metal, such as cold drawn, cold rolled, and seamless.
In the color marking system, a series of color symbols with a related color code is used to identify metals. The term color symbol refers to a color marking actually painted on the metal. The symbol is composed of one, two, or three colors and is painted on the metal in a conspicuous place. These color symbols correspond to the elements of which the metal is composed.
For further information on the metals used aboard ship, their properties and identification systems, refer to the TRAMAN, Hull Maintenance Technician 3 & 2, NAVEDTRA 10571-1, chapter 4.
In this chapter we have discussed some of the basic laws and principles of physics as they apply to the engineering ratings. We covered matter, magnetism, electricity, Ohm's law, Newton's laws, and mass and its different properties. Mechanical energy, thermal energy, and topics of energy transformations were described. We also provided you information on temperature, pressure definitions, principles of hydraulics, principles of pneumatics, and metals.
This chapter was provided to give you only the basis on which to expand your knowledge of electrical and mechanical fundamentals. It is important that you have a sound understanding of these laws and principles. The complex electrical and mechanical systems and the internal pressure-temperature relationships in an engineering plant make it imperative that you understand the material presented. If you have problems understanding this material, you should reread the pertinent portions until you have absorbed the basic concepts. You will use this information throughout your naval career. Study this information so you will have a good foundation of understanding within the engineering department of your ship.