Q7. What type of valve is used to regulate the flow of hydraulic fluid?

Q8. What are the three dimensions of any tubular product?

Q9. What are the three basic parts of a flexible hose?

Q10. What type of connector is used in a low-pressure pipe system?

Q11. When tubing nuts are tightened what tool should you use?

Q12. What type of seal application allows for a slight leakage for seal lubrication?

Q13. What is the most common metal seal used in Navy equipment?

Q14. What type of seal is ideally suited for both low-pressure and high-pressure applications?

Q15. What kind of leakage is caused by the wearing of seals and mated parts?

PNEUMATIC SYSTEMS

Learning Objective: Explain the operating principles of a pneumatic system. Identify operational characteristics and service procedures applicable to heavy-duty compressors.

The word pneumatics is a derivative of the Greek word pneuma, which means air, wind, or breath. Pneumatics can be defined as that branch of engineering science that pertains to gaseous pressure and flow. As used in this manual, pneumatics is the portion of fluid power in which compressed air, or other gas, is used to transmit and control power to actuating mechanisms.

This section discusses the basic principles of pneumatics, characteristics of gases, heavy-duty air compressors, and air compressor maintenance. It also discusses the hazards of pneumatics, methods of controlling contamination, and safety precautions associated with compressed gases.

BASIC PRINCIPLES OF PNEUMATICS

Gases differ from liquids in that they have no definite volume; that is, regardless of size or shape of the vessel, a gas will completely fill it. Gases are highly compressible, while liquids are only slightly so. Also, gases are lighter than equal volumes of liquids, making gases less dense than liquids.

Compressibility and Expansion of Gases

Gases can be readily compressed and are assumed to be perfectly elastic. This combination of properties gives gas the ability to yield to a force and return promptly to its original condition when the force is removed. These are the properties of air that is used in pneumatic tires, tennis balls, and other deformable objects whose shapes are maintained by compressed air.

Kinetic Theory of Gases

In an attempt to explain the compressibility of gases, consider the container shown in figure 3-49 as containing a gas. At any given time, some molecules are moving in one direction, some are travelling in other directions, and some may be in a state of rest. The average effect of the molecules bombarding each container wall corresponds to the pressure of the gas. As more gas is pumped into the container, more molecules are available to bombard the walls, thus the pressure in the container increases.

Increasing the speed with which the molecules hit the walls can also increase the gas pressure in a container. If the temperature of the gas is raised, the molecules move faster, causing an increase in pressure. This can be shown by considering the automobile tire. When you take a long drive on a hot day, the pressure in the tires increases and a tire that appeared to be soft in cool morning temperature may appear normal at a higher midday temperature.

Boyle's Law

When the automotive tire is initially inflated, air that normally occupies a specific volume is compressed into a smaller volume inside the tire. This increases the pressure on the inside of the tire.

Figure 3-49. - Molecular bombardment creating pressure.