Unit 23 - Compressor Quiz

Questions and Answers

Which of the following best describes the action of a dual-capacity reciprocating compressor? (Select all that apply)

One piston is attached to a quick-release connecting rod. When the crankshaft reverses direction, the connecting rod disconnects from the crankshaft, disabling the piston.

One piston is on a movable eccentric. When the crankshaft reverses direction, the eccentric centers on the crankshaft, disabling the piston. (correct)

One piston has a release valve built into the piston head. When the crankshaft reverses direction, the valve opens to prevent compression.

The vanes on a rotating vane compressor may be brought into contact with the cylinder walls by ___?

Centrifugal force

Spring pressure (correct)

Hydraulic pressure

All of the above

If a belt-driven compressor with a 6" pulley is being turned by a motor operating at 3600 RPM and equipped with a 3" pulley, the compressor's shaft will be turning at ____.

1800 RPM (correct)

3600 RPM

1200 RPM

7200 RPM

Which of the following best explains why the electrical connections and starting relays on hermetic compressors are typically installed outside the compressor housing?

Electrical arcing could break down and contaminate the refrigerant, leading to a compressor burnout. Signup and view all the answers

Reciprocating compressors can be classified by ____.

All of the above Signup and view all the answers

In reciprocating compressors, the intake and exhaust valves are located on the ___.

None of the above Signup and view all the answers

Which of the following types of valves have a valve stem that moves up and down in a valve guide?

Poppet valves Signup and view all the answers

One end of a connecting rod is attached to the piston and the other end is attached to the __.

Crankshaft journal Signup and view all the answers

Which of the following explains why exhaust valves present more problems than intake valves?

All of the above. Signup and view all the answers

A unique feature of screw compressors is the ability to control capacity through __ unloading.

Infinitely variable Signup and view all the answers

Which type of screw compressor is typically used in ammonia or other high-pressure systems?

Open-drive Signup and view all the answers

Which of the following statements regarding mufflers is false?

Mufflers are used only on hermetic compressors. Signup and view all the answers

Oil pumps are typically located __.

At one end of the compressor shaft Signup and view all the answers

Systems that have a capillary tube metering device do not require an unloader because ____.

The high side and low side pressures equalize during the 'Off' part of the cycle Signup and view all the answers

The volume between the top of the piston when it is at top dead center and the cylinder plate is known as __________ space.

Clearance Space Signup and view all the answers

A full-floating piston pin is free to turn in both the connecting rod bushing and the ________ bushings.

Piston Signup and view all the answers

In a(n) __________ lubrication system, the crank throw dips into the oil at each crankshaft revolution.

Splash Signup and view all the answers

A(n) _________ lubrication system uses a pump to distribute the oil.

Pressurized Signup and view all the answers

On open-drive and semi-hermetic compressors, the mating surfaces between bolted parts are usually sealed with _________.

Gasket Signup and view all the answers

A crankshaft and connecting rods convert the rotary motion of the motor shaft to _____ motion of the pistons.

Reciprocate Signup and view all the answers

The _______ type of reciprocating compressor has a long piston with an elliptical slot in the bottom of the piston skirt.

Scotch yoke Signup and view all the answers

The purpose of the _______ is to support the valve plate and to seal the cylinder so compression can occur.

Cylinder Head Signup and view all the answers

In a scroll compressor, gas pockets are formed between the fixed scroll and the _____ scroll.

Orbiting Signup and view all the answers

Adjustable ______ in a centrifugal compressor's inlet regulate the amount of refrigerant vapor flowing into the impeller.

Vanes Signup and view all the answers

A(n) overload _________ must be built into an oil pump to protect the system against excessively high oil pressure.

Relief Valve Signup and view all the answers

A(n)______ is used to temporarily reduce cylinder pressure during compressor start-up.

Unloader Signup and view all the answers

List two advantages of a multi-cylinder reciprocating compressor over a single-cylinder compressor of same capacity.

Reduce Vibration & Pressure Surges Signup and view all the answers

List the five basic types of compressors.

Scroll, Screw, Reciprocating, Centrifugal, Rotary Signup and view all the answers

Why are check valves used in the suction line on some rotary compressors?

Prevents backflow of refrigerant during off part Signup and view all the answers

What is the purpose of a shaft seal?

Prevent leakage Signup and view all the answers

Why must the clearance space be kept as small as possible?

Force more vapor into the high side. Signup and view all the answers

What is the purpose of the stationary blade in a stationary blade rotary compressor?

Traps vapor into pocket Signup and view all the answers

What two locations are mufflers sometimes used on a compression system?

Inlet & exhaust line Signup and view all the answers

List three basic parts of a reed valve assembly.

Valve retainer, discharge valve & suction valve, valve plate, valve stop Signup and view all the answers

What is used to minimize the amount of compressed refrigerant that can leak past the piston into the crankcase?

Piston Rings Signup and view all the answers

What are the lubrication methods in reciprocating?

Splash, Force Signup and view all the answers

Define oil pressure.

The difference between crankcase pressure and oil pump pressure - Net Oil Pressure = Oil Pump Press - Crankcase Pressure Signup and view all the answers

Define capacity control.

The design cooling load for the maximum load anticipated at conditions. Signup and view all the answers

What could operating at lower evaporator temperatures result in?

Frost coils, Poor oil return, Poor Humidity, Short Cycling Signup and view all the answers

What are the mechanical unloaders?

Suction bypass, Suction Cutoff, Hydraulic Signup and view all the answers

What are the capacity control methods for each compressor?

Reciprocating --> On & Off, Multiple compressors; Rotary --> Speed Control; Scroll --> Speed & On/Off; Screw --> Speed Control; Centrifugal --> Variable inlet vanes Signup and view all the answers

What are factors that affect compressor efficiency?

Piston displacement, Suction/discharge valves, Clearance Pocket, Number of Cylinder Signup and view all the answers

Study Notes

Compressor Functionality and Components

Dual-capacity reciprocating compressors use a movable eccentric to disable one piston when the crankshaft reverses.
Rotating vane compressors bring vanes into contact with cylinder walls primarily through spring pressure.
A 6” pulley driven by a 3” pulley motor operates at a compressor shaft speed of 1800 RPM.
Electrical connections on hermetic compressors are outside the housing to prevent refrigerant contamination from electrical arcing.

Classification and Valve Mechanics

Reciprocating compressors can be classified by cylinder arrangement, number of cylinders, and type of crankshaft.
Intake and exhaust valves in reciprocating compressors are located externally from the cylinder head and valve block.
Poppet valves have a valve stem that moves vertically within a guide, unlike reed and check valves.

Connecting Rod and Compressor Systems

Connecting rods attach the piston to the crankshaft journal, linking reciprocating and rotary motion.
Exhaust valves face issues due to higher operating temperatures and carbon accumulation compared to intake valves.
Screw compressors have the advantage of infinitely variable capacity control through unloading.

Compressor Types and Features

Open-drive screw compressors are typically used in high-pressure ammonia systems.
Mufflers can be installed on both the inlet and outlet of compressors to reduce noise from gas pulsation.
Oil pumps are typically situated at one end of the compressor shaft, ensuring effective lubrication.

Specialized Components and Operational Insights

Capillary tube systems balance high and low side pressures during off cycles, eliminating the need for unloaders.
Clearance space is defined as the volume between the piston at top dead center and cylinder plate, kept minimal to enhance vapor force into the high side.
The Skotch yoke reciprocating compressor features a long piston with an elliptical slot for efficiency.

Scroll and Centrifugal Compressor Mechanics

In scroll compressors, gas pockets are formed between fixed and orbiting scrolls, creating continuous compression.
Adjustable vanes in centrifugal compressors modulate refrigerant vapor flow into the impeller.
Overload relief valves are crucial in oil pumps, protecting against excessive pressure.

Start-Up and Maintenance Considerations

Unloaders temporarily reduce cylinder pressure during compressor start-up, enhancing efficiency.
Key components in a reed valve assembly include the valve retainer, discharge valve, suction valve, and valve plate.
Piston rings minimize refrigerant leakage into the crankcase, ensuring system integrity.

Lubrication and Efficiency Factors

Reciprocating compressors commonly utilize splash and force lubrication methods.
Oil pressure is defined as the difference between crankcase pressure and oil pump pressure.
Capacity control defines the design cooling load based on anticipated maximum conditions.

Effects of Operating Conditions

Lower evaporator temperatures may lead to frost on coils, poor oil return, humidity control issues, and short cycling.
Mechanical unloaders include suction bypass, suction cutoff, and hydraulic types, enhancing operational flexibility.

Compressor Efficiency Considerations

Factors affecting compressor efficiency include piston displacement, valve performance, clearance pockets, and cylinder counts.

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Test your knowledge about dual-capacity reciprocating compressors with this quiz. Through flashcards, explore the mechanics and functionalities of these crucial machines. Perfect for students and professionals in the HVAC field.