4BE3 U2 C3 Review
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Questions and Answers

What is the primary purpose of compressed air in SCBA used by firefighters?

  • To provide breathable air (correct)
  • To operate pneumatic tools
  • To cool the environment
  • To extinguish fires

    • Which of the following is an example of the use of compressed gases in the food industry?

  • Welding
  • Pipeline transportation
  • Refrigeration
  • Whipped cream (correct)

    • What is the key difference between liquids and gases in terms of compression?

  • Liquids are more versatile than gases
  • Liquids are used more frequently than gases
  • Gases are heavier than liquids
  • Gases can be compressed, while liquids cannot (correct)

    • What is the primary focus of the construction and operation of compressors?

    <p>Managing pressure, volume, temperature, and velocity</p> Signup and view all the answers

    Which type of compressor accelerates the gas using impellers or blades?

    <p>Dynamic compressor</p> Signup and view all the answers

    What is the principle that explains the relationship between pressure and velocity?

    <p>Bernoulli's principle</p> Signup and view all the answers

    What is the primary function of dynamic compressors?

    <p>To convert low-pressure air into high-pressure air</p> Signup and view all the answers

    What type of compressor is commonly used to pump air into bike tires or soccer balls?

    <p>Reciprocating compressor</p> Signup and view all the answers

    In a single-acting reciprocating compressor, how many compression strokes occur per crankshaft revolution?

    <p>One</p> Signup and view all the answers

    What prevents the gas from leaking past the piston in a reciprocating compressor?

    <p>Piston rings</p> Signup and view all the answers

    In a double-acting reciprocating compressor, how many compression strokes occur per crankshaft revolution?

    <p>Two</p> Signup and view all the answers

    What determines the type of compressor used in an application?

    <p>Maximum operating pressure required</p> Signup and view all the answers

    What is the purpose of the suction valve in a reciprocating compressor?

    <p>To draw air into the cylinder</p> Signup and view all the answers

    What is the advantage of using a two-stage compressor over a single-stage compressor?

    <p>It can produce a higher pressure of compressed air</p> Signup and view all the answers

    In a single-stage compressor with multiple cylinders, what is the pressure of the air leaving the discharge valve?

    <p>The same from each cylinder</p> Signup and view all the answers

    Why is a two-stage compressor used in applications where the required air pressure is high?

    <p>Because it can produce a higher pressure of compressed air</p> Signup and view all the answers

    What happens when liquid enters the compressor?

    <p>The reed and the beam are forced upwards</p> Signup and view all the answers

    What is the purpose of the large port opening in the compressor?

    <p>To allow the compressed vapour and trapped liquid to escape</p> Signup and view all the answers

    How does the diaphragm valve in Figure 10(c) operate?

    <p>The diaphragm flexes upward due to gas pressure</p> Signup and view all the answers

    What is the importance of tightness and proper seating of compressor valves?

    <p>It prevents hot compressed vapour from flowing back into the compressor</p> Signup and view all the answers

    How are leaking compressor valves typically repaired?

    <p>By replacing the reeds and discs, and resurfacing the seats</p> Signup and view all the answers

    What type of compressor is shown in Figure 11?

    <p>Sliding vane compressor</p> Signup and view all the answers

    What is the advantage of the sliding vane compressor in terms of starting?

    <p>It requires low starting torque</p> Signup and view all the answers

    What is the common drive used for sliding vane compressors?

    <p>Directly connected electric motor</p> Signup and view all the answers

    What is the shape of the impellers in a rotary lobe compressor?

    <p>Figure-eight</p> Signup and view all the answers

    What is the advantage of rotary compressors in terms of valves?

    <p>They do not require inlet and discharge valves</p> Signup and view all the answers

    What is the purpose of the intercooler in a reciprocating compressor?

    <p>To cool the gas before entering the second stage</p> Signup and view all the answers

    What is the main function of the piston rings in a compressor?

    <p>To provide a flexible seal to prevent the compressed vapour from escaping</p> Signup and view all the answers

    What is the main difference between a one-piece and a two-piece compressor block?

    <p>The way the crankcase and cylinders are cast</p> Signup and view all the answers

    What is the purpose of the wrist pin in a compressor?

    <p>To connect the piston to the connecting rod</p> Signup and view all the answers

    What is the advantage of using a two-stage compressor over a single-stage compressor?

    <p>It produces a larger volume of compressed air at moderate pressure</p> Signup and view all the answers

    What is the purpose of the crankshaft in a reciprocating compressor?

    <p>To move the pistons up and down</p> Signup and view all the answers

    What is the difference between a flexible reed valve and a non-flexible ring valve?

    <p>The way they open and close</p> Signup and view all the answers

    What is a characteristic of rotary lobe compressors?

    <p>Compact design and oil-free air</p> Signup and view all the answers

    What is the purpose of the compressor bearings in a reciprocating compressor?

    <p>To reduce friction between moving parts</p> Signup and view all the answers

    How do the impellers in a rotary lobe compressor operate?

    <p>One is driven directly, and the other maintains relative position</p> Signup and view all the answers

    What is a benefit of rotary screw compressors?

    <p>Compact design and vibration-free operation</p> Signup and view all the answers

    What is the advantage of using a radial cylinder arrangement in a reciprocating compressor?

    <p>It provides a more balanced operation of the compressor</p> Signup and view all the answers

    What is the purpose of the timing gears in a rotary lobe compressor?

    <p>To maintain the relative position of the impellers</p> Signup and view all the answers

    What is the purpose of the oil ring in a compressor piston?

    <p>To distribute lubricating oil evenly over the cylinder wall</p> Signup and view all the answers

    What is a characteristic of scroll compressors?

    <p>Tolerance of liquids in gases</p> Signup and view all the answers

    What is the principle of operation of dynamic compressors?

    <p>Bernoulli's principle</p> Signup and view all the answers

    What is the advantage of centrifugal compressors over other types?

    <p>Simplicity of operation and minimal maintenance</p> Signup and view all the answers

    What is the function of the diffuser vanes in a centrifugal compressor?

    <p>To convert kinetic energy to potential energy</p> Signup and view all the answers

    What is the maximum pressure output of a single-stage centrifugal compressor?

    <p>300 kPa</p> Signup and view all the answers

    What is the purpose of the volute shaped casing in a centrifugal compressor?

    <p>To convert velocity into pressure</p> Signup and view all the answers

    What is the advantage of centrifugal compressors over positive displacement type?

    <p>Simple and rugged construction with low maintenance requirements</p> Signup and view all the answers

    What is the purpose of adjustable inlet vanes in a single-stage compressor?

    <p>To change the capacity of the unit</p> Signup and view all the answers

    What is the characteristic of air driven hand tools?

    <p>They are often lighter in weight</p> Signup and view all the answers

    What is the advantage of compressed air machinery over steam driven machinery?

    <p>Transmission losses are less</p> Signup and view all the answers

    What is the purpose of vanes at the eye of the impeller in a centrifugal compressor?

    <p>To provide shockless entry to the impeller</p> Signup and view all the answers

    What is the characteristic of an axial flow compressor?

    <p>The airflow is axial to the compressor shaft</p> Signup and view all the answers

    What is the purpose of a multistage compressor?

    <p>To increase the pressure ratio</p> Signup and view all the answers

    What is the disadvantage of compressed air tools compared to electrically driven tools?

    <p>They are usually more expensive</p> Signup and view all the answers

    What is the purpose of a compressor system in an industrial setting?

    <p>To operate pneumatic control systems</p> Signup and view all the answers

    What is the advantage of compressed air machinery over electric machinery in explosive atmospheres?

    <p>It can be used safely in explosive atmospheres</p> Signup and view all the answers

    What is the purpose of a dryer in a compressed air system?

    <p>To remove moisture from the compressed air</p> Signup and view all the answers

    Why are oil-free rotary compressors used in some processes?

    <p>To prevent mixing oil with the air</p> Signup and view all the answers

    What is the purpose of pressure regulators in a compressed air system?

    <p>To reduce the pressure of the compressed air</p> Signup and view all the answers

    Why are automatic drain valves installed in receivers?

    <p>To drain off liquids that collect at the bottom of the receivers</p> Signup and view all the answers

    What is the purpose of an air filter in an air compressor system?

    <p>To prevent dust and other particles from being carried into the compressor</p> Signup and view all the answers

    Why are compressors installed in gas plants?

    <p>To boost the pressure of the gas to meet pipeline requirements</p> Signup and view all the answers

    What is the purpose of a suction scrubber in a natural gas compressor system?

    <p>To remove liquids from the gas stream</p> Signup and view all the answers

    What is the advantage of a compressor skid?

    <p>It is more cost-effective than constructing a new system on-site</p> Signup and view all the answers

    Why are certain applications, like instrument air, required to have dry, clean, and oil-free air?

    <p>Because they require specific air quality</p> Signup and view all the answers

    What is the concern in compressing natural gas?

    <p>Preventing liquids from entering the compressor</p> Signup and view all the answers

    What is the function of the high-level float or probe in a scrubber?

    <p>To signal the compressor to shut down if the level gets too high</p> Signup and view all the answers

    What is the purpose of the intercooler in a compression system?

    <p>To remove heat from the gas</p> Signup and view all the answers

    What is the purpose of the coalescer or knockout drum in a compression system?

    <p>To remove moisture from the gas</p> Signup and view all the answers

    What happens if the suction valve or discharge valve of a reciprocating compressor is closed?

    <p>The compressor will recirculate the gas</p> Signup and view all the answers

    What is the primary function of a compressor in a refrigeration system?

    <p>To draw the refrigerant from the evaporator and raise its pressure</p> Signup and view all the answers

    What is the advantage of a hermetic compressor?

    <p>It does not require shaft sealing</p> Signup and view all the answers

    What type of compressor is commonly used in refrigeration systems?

    <p>All of the above</p> Signup and view all the answers

    What is the purpose of the aftercooler in a compression system?

    <p>To remove heat from the gas</p> Signup and view all the answers

    What happens to the gas as it moves through the intercooler?

    <p>It becomes cooler</p> Signup and view all the answers

    What is the purpose of the scrubber in a compression system?

    <p>To remove moisture from the gas</p> Signup and view all the answers

    What is the primary reason why gases can be compressed?

    <p>Because they can be forced into a smaller volume</p> Signup and view all the answers

    What is the main difference between positive displacement and dynamic compressors?

    <p>The way they accelerate the gas</p> Signup and view all the answers

    What is the primary function of the heat variable in compressor management?

    <p>To control the temperature of the gas</p> Signup and view all the answers

    In which industry is compressed hydrocarbons used for transportation?

    <p>Natural gas industry</p> Signup and view all the answers

    What is the principle that explains the relationship between pressure and velocity in compressors?

    <p>Bernoulli's principle</p> Signup and view all the answers

    What is the main application of compressed air in hospitals and ambulances?

    <p>Providing breathable air</p> Signup and view all the answers

    What is the primary difference between a dynamic compressor and a positive displacement compressor?

    <p>The method of compression</p> Signup and view all the answers

    What is the purpose of the piston rings in a reciprocating compressor?

    <p>To seal the piston and cylinder</p> Signup and view all the answers

    What happens when the piston moves downward in a single-acting reciprocating compressor?

    <p>The suction valve opens and the discharge valve closes</p> Signup and view all the answers

    What is the advantage of a two-stage compressor over a single-stage compressor?

    <p>Higher pressure output</p> Signup and view all the answers

    What is the purpose of the crank end suction valve in a double-acting reciprocating compressor?

    <p>To draw air into the cylinder</p> Signup and view all the answers

    What is the characteristic of a compressor with multiple cylinders?

    <p>Higher volume of compressed air</p> Signup and view all the answers

    What is the purpose of the discharge valve in a reciprocating compressor?

    <p>To discharge compressed air from the cylinder</p> Signup and view all the answers

    Why are centrifugal compressors often used in power plants?

    <p>Because they can handle high volumes of air</p> Signup and view all the answers

    What is the difference between a single-acting and double-acting reciprocating compressor?

    <p>The compression and discharge process</p> Signup and view all the answers

    What is the purpose of cooling the gas in a two-stage compressor?

    <p>To reduce the temperature and volume of the gas</p> Signup and view all the answers

    What is the typical arrangement of cylinders in a single-acting type compressor?

    <p>Vertical</p> Signup and view all the answers

    What is the advantage of using a two-cylinder compressor over a single-cylinder compressor?

    <p>Higher volume of compressed air</p> Signup and view all the answers

    What is the purpose of the wrist pin in a compressor piston?

    <p>To connect the piston to the connecting rod</p> Signup and view all the answers

    What is the function of the crankshaft in a compressor?

    <p>To convert the linear motion of the piston into rotary motion</p> Signup and view all the answers

    What is the purpose of the intercooler in a compressor?

    <p>To reduce the temperature and volume of the gas</p> Signup and view all the answers

    What is the advantage of a two-piece compressor block over a one-piece block?

    <p>It allows for easier replacement of cylinder liners</p> Signup and view all the answers

    What is the purpose of the valve guard in a flexible reed valve?

    <p>To restrict the movement of the valve</p> Signup and view all the answers

    What is the function of the compressor bearings in a compressor?

    <p>To support the crankshaft and allow it to rotate smoothly</p> Signup and view all the answers

    What is the purpose of the piston rings in a compressor?

    <p>To provide a flexible seal to prevent compressed vapour from escaping</p> Signup and view all the answers

    What is the advantage of using a two-stage compressor over a single-stage compressor?

    <p>It allows for higher compression ratios</p> Signup and view all the answers

    What is the consequence of liquid entering the compressor?

    <p>The high pressure at the end of the stroke forces the reed and the beam upwards</p> Signup and view all the answers

    What is the purpose of the tightness and proper seating of compressor valves?

    <p>To prevent leakage of hot compressed vapour</p> Signup and view all the answers

    What is the characteristic of a rotary compressor that makes it less efficient than a reciprocating compressor?

    <p>It has a lower compression ratio</p> Signup and view all the answers

    What is the function of the flexible coupling in a two-stage sliding vane compressor?

    <p>To connect the two compressor shafts</p> Signup and view all the answers

    What is the shape of the impellers in a rotary lobe compressor?

    <p>Figure-eight</p> Signup and view all the answers

    What is the consequence of leaking compressor valves?

    <p>The compressor output is reduced</p> Signup and view all the answers

    What is the function of the ring in a non-flexible ring valve?

    <p>To cover a series of ports</p> Signup and view all the answers

    What is the advantage of a rotary compressor in terms of valves?

    <p>It does not require inlet or discharge valves</p> Signup and view all the answers

    What is the function of the vanes in a sliding vane compressor?

    <p>To move out against the casing wall due to centrifugal force</p> Signup and view all the answers

    What is the maximum discharge pressure of a sliding vane compressor?

    <p>1000 kPa</p> Signup and view all the answers

    What is the primary function of the timing gears in a rotary lobe compressor?

    <p>To maintain the relative position of the impellers</p> Signup and view all the answers

    Which type of compressor is more tolerant of liquids in gases?

    <p>Scroll compressor</p> Signup and view all the answers

    What is the maximum pressure output of a two-stage rotary lobe compressor?

    <p>200 kPa</p> Signup and view all the answers

    What is the purpose of the diffuser vanes in a centrifugal compressor?

    <p>To convert kinetic energy to potential energy</p> Signup and view all the answers

    Which type of compressor uses Bernoulli's principle to compress air?

    <p>Dynamic compressor</p> Signup and view all the answers

    What is the advantage of a rotary screw compressor over a rotary lobe compressor?

    <p>Higher speed range</p> Signup and view all the answers

    What is the purpose of the volute shaped casing in a centrifugal compressor?

    <p>To further increase the pressure of the air</p> Signup and view all the answers

    What is the primary advantage of a rotary lobe compressor?

    <p>Compact design and low vibration</p> Signup and view all the answers

    What is the characteristic of a single-stage centrifugal compressor?

    <p>Single impeller design</p> Signup and view all the answers

    What is the primary advantage of a scroll compressor?

    <p>Quiet operation</p> Signup and view all the answers

    What is the primary function of the diffuser vanes in a single-stage centrifugal compressor?

    <p>To change the operating characteristics of the compressor</p> Signup and view all the answers

    What is the advantage of using electric motors or reciprocating type internal combustion engines as drivers for centrifugal compressors?

    <p>They provide high speeds required for the compressor</p> Signup and view all the answers

    What is the primary function of the moving blades in an axial flow compressor?

    <p>To increase the velocity of the air</p> Signup and view all the answers

    What is the difference between a compressor and a compressor system?

    <p>A compressor is a component of a larger system, while a compressor system is a standalone unit</p> Signup and view all the answers

    What is the advantage of using compressed air to drive tools and other machinery over the use of electricity or steam?

    <p>Compressed air machines cannot be damaged by overloading</p> Signup and view all the answers

    What is the primary function of the adjustable inlet vanes in a single-stage compressor?

    <p>To control the amount of air that flows to the impeller</p> Signup and view all the answers

    What is the primary function of the fixed blades in an axial flow compressor?

    <p>To convert high velocity air to low velocity air</p> Signup and view all the answers

    What is the advantage of using centrifugal compressors over positive displacement type compressors?

    <p>They have simpler and more rugged construction</p> Signup and view all the answers

    What is the primary function of the impeller in a centrifugal compressor?

    <p>To increase the velocity of the air</p> Signup and view all the answers

    What is the disadvantage of using compressed air tools compared to electrically driven tools?

    <p>They are usually more expensive</p> Signup and view all the answers

    What is the purpose of a receiver in a compressed air system?

    <p>To store compressed air</p> Signup and view all the answers

    Why are oil-free rotary compressors used in certain applications?

    <p>To prevent mixing oil with the air</p> Signup and view all the answers

    What is the purpose of a suction scrubber in a natural gas compressor system?

    <p>To remove liquids from the gas stream</p> Signup and view all the answers

    What is the advantage of a compressor skid in natural gas compression?

    <p>It is compact and more cost-effective</p> Signup and view all the answers

    Why is a two-stage compressor used in certain applications?

    <p>To obtain higher pressures than a single-stage compressor</p> Signup and view all the answers

    What is the purpose of automatic drain valves in receivers?

    <p>To drain off liquids that collect at the bottom of the receivers</p> Signup and view all the answers

    What is the purpose of a dryer in a compressed air system?

    <p>To remove moisture from the compressed air</p> Signup and view all the answers

    Why are compressors installed in gas plants?

    <p>To boost the pressure of gas from wells to meet pipeline requirements</p> Signup and view all the answers

    What is the purpose of a pressure relief valve in a compressor system?

    <p>To prevent over-pressurization of the system</p> Signup and view all the answers

    Why are filters installed in a compressed air system?

    <p>To absorb oil from the air</p> Signup and view all the answers

    What is the primary function of the compressor in a refrigeration system?

    <p>To draw the refrigerant from the evaporator</p> Signup and view all the answers

    What is the purpose of the automatic drain valves in a compression system?

    <p>To remove moisture from the compressed gas</p> Signup and view all the answers

    What is the characteristic of open type compressor housings?

    <p>They are suitable for a variety of drives</p> Signup and view all the answers

    What is the purpose of the coalescer or knockout drum in a compression system?

    <p>To minimize the moisture entrained in the gas leaving the unit</p> Signup and view all the answers

    What is the difference between hermetic and semi-hermetic compressor housings?

    <p>Hermetic housings are completely sealed, while semi-hermetic housings are not</p> Signup and view all the answers

    What is the purpose of the intercooler in a compression system?

    <p>To cool the gas as it moves from the first stage to the second stage</p> Signup and view all the answers

    What is the advantage of using a reciprocating compressor in a refrigeration system?

    <p>It can operate within a closed loop</p> Signup and view all the answers

    What is the purpose of the automatic recirculation or bypass control valve in a compression system?

    <p>To continue to circulate gas through the compressor until it can flow out the discharge again</p> Signup and view all the answers

    What is the primary function of the compressor in a compression system?

    <p>To reduce the volume of the gas</p> Signup and view all the answers

    What is the purpose of the aftercooler in a compression system?

    <p>To cool the gas after it has been compressed</p> Signup and view all the answers

    What is the main purpose of a safety head in a refrigeration system?

    <p>To prevent damage to the compressor from liquid refrigerant</p> Signup and view all the answers

    What is the primary difference between a serviceable semi-hermetic screw compressor and a hermetic type?

    <p>The ability to service the internal mechanisms</p> Signup and view all the answers

    What is the mechanism that prevents the safety head from lifting during normal operation?

    <p>A heavy spring</p> Signup and view all the answers

    What is the consequence of liquid refrigerant entering the cylinder of a reciprocating compressor?

    <p>Hydraulic pressure damage</p> Signup and view all the answers

    What is the purpose of the spring in the safety head of a compressor?

    <p>To hold the valve assembly in place</p> Signup and view all the answers

    What is the benefit of the safety head in a refrigeration system?

    <p>Prevention of compressor damage from liquid refrigerant</p> Signup and view all the answers

    What is the primary purpose of the safety head in a refrigeration compressor?

    <p>To prevent damage from hydraulic pressure caused by trapped liquid refrigerant</p> Signup and view all the answers

    What is the key difference between hermetic and semi-hermetic compressor designs?

    <p>The ability to service internal mechanisms</p> Signup and view all the answers

    In a refrigeration system, why is the potential of liquid entering the cylinder of a reciprocating compressor higher?

    <p>Because the refrigerant is being converted from a gas to a liquid</p> Signup and view all the answers

    What is the purpose of the spring in a safety head?

    <p>To hold the valve assembly in place during normal operation</p> Signup and view all the answers

    In what type of compressors is the safety head principle often applied?

    <p>Reciprocating compressors with ring plate valves</p> Signup and view all the answers

    What happens when the pressure in the cylinder of a reciprocating compressor becomes too high due to trapped liquid refrigerant?

    <p>The safety head lifts, allowing the liquid to pass into the discharge line</p> Signup and view all the answers

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