Between regular maintenance inspections, be alert for signs of motor or pump trouble. Common symptoms are listed in table 6-3. Correct any trouble immediately and AVOID COSTLY REPAIR AND SHUTDOWN.

Q6. What is total discharge head?

Q7. The amount of suction lift a pump can provide is determined by what three factors?

Q8. What are the five categories of pumps?

Q9. A rotary pump is classified as what type of pump?

Q10. What are the types of rotary pumps?

Q11. Most reciprocating pumps used in the Navy are of what four types?

Q12. What is the only moving part in a centrifugal pump?

Q13. When the velocity of a fluid in a pump increases, what happens to the pressure head?

Q14. What pumps are used exclusively for well pumping?

Q15. When an elbow is installed horizontally in suction piping, what happens to the liquid entering the pump?

Q16. Why should you avoid high spots, such as loops, in discharge piping?

Q17. Widely fluctuating discharge pressure gauge indicates what type of problem?

Q18. On grease-lubricated bearings, what is the most common problem caused by excessive grease?

Q19. What advantage does a mechanical shaft seal have over packing?

Q20. Using table 6-2, how often should you inspect the packing on a pump?

Q21. Using table 6-2, removal and inspection of the rotating elements of a pump should be accomplished how often?

AIR COMPRESSORS

LEARNING OBJECTIVE: Recognize types of air compressor components, accessories, systems, operation of these systems, and maintenance procedures.

Air compressors are devices or machines that compress air. In compression, air at a normal atmospheric temperature is taken in and sqeezed or pressed by a moving element within a confined space. The volume of air is thus reduced, but the pressure, or force, of the volume of air exerted has increased considerably. Thus the air develops energy or power that can be put to some useful purpose in other machines. The compressed air need not be put to work immediately but can be stored in tanks to preserve and maintain its pressure.

Compressed air can be taken from storage bottles or flasks and used to start diesel engines; that is, the compressed air is introduced into the diesel cylinders where, by its pressure, it forces the pistons to reciprocate until ignition temperature is reached. We have seen how compressed air forces water to rise in wells. Air compressors also drive, or power, a wide variety of pneumatic tools in construction work. The types of air compressors include reciprocating, centrifugal, and rotary; however, only reciprocating compressors are discussed in the following paragraphs. In basic design and function, these compressors are similar to the pumps with the same names. In fact, air compressors are sometimes referred to as air pumps. Rather than discharging liquid at relatively high pressure, air compressors discharge air (which is considered a fluid) at high pressure. Like pumps, compressors require some external source of mechanical power to do this work. Prime movers for air compressors may be electric motors, internal combustion engines, steam turbines, and so on. The majority of air compressors used throughout the Navy are driven by electric motors.

RECIPROCATING AIR COMPRESSORS

One of the most commonly used air compressors in the naval service is the reciprocating air compressor. It compresses air in the same manner as a diesel engine. A reciprocating piston alternately draws in and then compresses the trapped air in a cylinder. Since there is no internal combustion, the cycle of the reciprocating air compressor is reduced or simplified to two strokes- suction (intake) and compression. Instead of operating the valves by cam action, as in internal combustion engines, the intake and discharge valves of the reciprocating air compressor operate on the principle of differential pressure overcoming spring tension,