Mechanical Engineering Unit 13 Unit Review Questions Answer Keygo Back Index What The Only Thing All

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UNIT 13 REVIEW QUESTIONS ANSWER KEY GO BACK TO INDEX

13-1) What is the only thing all compressors must pump?

13-2) List the major types of compressors by mechanical design.

Reciprocating, rotary, scroll, screw, centrifugal

13-3) Explain the difference between a positive displacement compressor and a non-

positive displacement compressor.

13-4) What is the function of the compressor within the refrigeration cycle?

13-5) What factors affect compressor capacity?

13-6) Why are the intake ports on low- and medium-temperature compressors larger

in size than the intake ports on air conditioning compressors?

13-7) Why are hermetic compressors designed for specific applications?

13-8) Why is more horsepower required to produce a ton of cooling at an evaporator

saturation temperature of 0°F than at 40°F?

13-9) What is the purpose of the shaft seal on an open compressor?

13-10) List two advantages of open drive compressors.

13-11) What is hermetic compressor?

13-12) What is an advantage of the semi-hermetic compressor design?

13-13) What opens and closes the valves in a reciprocating compressor?

13-14) What is the clearance volume of a reciprocating compressor?

13-15) What are some common applications for rotary compressors?

13-16) How does a rolling piston rotary compressor work?

13-17) How does a rotary-vane compressor work?

13-18) How does a scroll compressor work?

13-19) What rotates in a scroll compressor?

13-20) Explain what compliance means for scroll compressors.

13-21) Why should hermetic compressors not be operated in a vacuum?

13-22) What is the purpose of compressor capacity control?

13-23) How does a two-step scroll compressor achieve capacity reduction?

13-24) What controls the internal unloading solenoid coil of the two-step scroll?

13-25) At what two capacities can a digital scroll compressor operate?

13-26) What gives the digital scroll the appearance of varying its capacity?

13-27) What is the lowest percentage of full capacity that a digital scroll can be

operated and why?

13-28) What are the three different screw compressor types?

13-29) How are the small gaps on the screw compressor sealed?

13-30) Why is the oil separator important to screw compressors?

13-31) How does a centrifugal compressor work?

13-32) What type of systems are most centrifugal compressors used on?

13-33) How can oil be delivered to internal moving compressor parts?

13-34) What is the purpose of a crankcase heater on a compressor?

13-35) List ways to change the compressor capacity to match the system load.

13-36) Above what temperature do most refrigerant oils begin to break down

chemically?

13-37) What is the compression ratio of a compressor with a suction pressure of 110

psig and a discharge pressure of 360 psig?

13-38) Why is it incorrect to close the suction line service valve to test a compressor?

13-39) What problem can be caused if liquid refrigerant enters the compressor?

13-40) What is cylinder gas reexpansion and why is it a problem?

13-41) How can a technician tell is a failed compressor has been operating at

excessive discharge temperatures?

13-42) How can a technician determine if an operating compressor is experiencing

floodback?