Chapter 19/20 - Compressors/Compressor Safety
What size horsepower is a fully hermetic compressor built with?
1/6 hp up to 20 hp
What type of compressor is extensively used for air conditioning in commercial air conditioning
Centrifugal compressor
The compressor is known as the "______" of the system.
Heart
What are the two basic types of rotary compressor?
Stationary-blade rotating-vane
How are the motor and compressor of a semi-hermetic compressor usually arranged?
horizontally
How are the compressor and motor of a hermetic compressor mounted?
inside the hermetic dome with springs
What do the compressor's valves do?
regulate the flow of refrigerant into and out of the cylinders
What determines the size of a compressor used in commercial applications?
size is determined by the cooling capacity required
What is a crankcase heater
A device that warms the compressor crankcase to evaporate liquid refrigerant trapped in the oil
What is meant by a semi-hermetic compressor?
A semi-hermetic compressor is a compressor that contains a motor and a compressor inside a multipart shell that is bolted together.
what is the purpose of a compressor servic valve?
Allows service Tech to attach gauges add refrigerant and oil isolate the compressor from the rest of the system
Which type of open-drive compressor uses a belt connected to a pulley on the drive motor to the pulley on the compressor's shaft?
Belt-driven compressor
What are the two types of open-drive compressors?
Belt-driven compressor Direct-drive compressor
how does the muffler work?
By allowing gas to expand inside the muffler chamber, smoothing out the flow.
how is most of the heat removed from the compressor
By the oil circulating through the compressor
How do pressure lubricating systems work?
By using a small oil pump to force oil to the main bearings
What does the compressor do?
Compresses low-temp/pressure vapor into high-temp/pressure vapor. Pumps refrigerant throughout the system.
What is a muffle and where is it located
Devise installed on the discharge line to help reduce noise
Which type of open-drive compressor uses a coupling to connect the shaft of an electric motor or engine directly to the compressor shaft?
Direct-drive compressor
What two mechanisms can be used to drive refrigeration motors?
Electric motors Internal combustion engines
T/F: There is usually a pressure control connected to the engine's throttle on the high side discharge line.
False. It is connected on the low side suction line.
What is the purpose of the shaft seal?
It creates a leak-proof seal between the shaft and the case where it emerges preventing refrigerant from leaking out and air from leaking in.
How is an open-drive compressor energized?
It is driven by a mechanical power source that is separate from the compressor unit (i.e. electric motor)
What happens if there is an unbalanced loading of the compressor shaft due to improper belt tension or drive shaft misalignment?
It will increase the wear of the shaft seal, which will allow leaks to occur.
What's the purpose of the crankcase heater
Keeps oil warm and thin during cold temps
Where are open-drive compressors primarily used?
Large commercial and industrial refrigeration applications
What causes a high compression ratio?
Low suction pressure high discharge pressure
How do reed valves work?
Made of strips of spring steel that bend to open the valve passage, and spring back to close the valve passage.
how are motors cooled in a refrigeration system?
Most are cooled by passing suction vapors and return oil over the windings.
list types of lubricating systems
Oil circulating throughout via unit splash method
What are the two elements that make up the shaft seal do?
One element turns with the shaft, the other element is stationary and mounted to the case.
What are compressors driven by an external motor called?
Open-drive compressors
What do the pistons, piston ring, and piston pins do?
Piston: the part that actually compresses the gas Piston ring: a split metal ring that has a larger outside diameter than inside diameter which keeps the piston seated in the groves on the crankshaft. Piston pins: connects the piston to the connecting rod
What are poppet valves?
Poppet valves have a large valve head that seals against a matching seat in the valve plate
What are the five types of compressors that are used in the refrigeration and air conditioning industry?
Reciprocating Rotary Scroll Screw Centrifugal
Which type of compressor is used in domestic refrigeration, residential air conditioning, commercial air conditioning and commercial refrigeration?
Reciprocating compressor (fully-hermetic)
Which type of compressor is primarily used in commercial and residential air conditioning as well as industrial refrigeration?
Reciprocating compressor (open-drive)
Which type of compressor is used in commercial air conditioning and commercial refrigeration?
Reciprocating compressor (semi-hermetic)
what are compressor fans for?
Reduce compression ratio
What are the two most common types of compressor valves used in refrigeration compressors.
Reed valves (also known as flapper valves) Poppet valves
Which type of compressor is used for domestic refrigeration?
Rotary compressor
Which type of compressor is primarily used in large commercial air conditioning, commercial refrigeration, and industrial refrigeration applications?
Screw compressor
Which type of compressor is primarily used in residential air conditioning, commercial air conditioning, and commercial refrigeration?
Scroll compressor
list compressor accessories
Service valves Mufflers cooling systems lubricating system unloader sealing devices crankcase heaters
How are cylinders cooled?
Small compressors have cooling fins located on their exterior surfaces, and larger compressors use water jackets surrounding the cylinders
what are the two methods for lubricating a reciprocating compressor?
Splash method pressure method
What is the function of an unloader?
Temporarily reduce the pressure during startup used to vary the pumping capacity of certain compressors during low-load demands
What does the compression rings do?
The compression rings are the upper rings that prevent pressurized refrigerant from blowing past the piston.
The compressor pulley is larger than the motor pulley, will the compressor turn slower or faster than the drive motor?
The compressor turns slower than the drive motor.
What is the eccentric?
The essentric is the section of the shaft that is larger and has a different center from the rest.
What is meant by a hermetic compressor?
The motor is sealed inside the same housing as the compressor.
What does the oil ring do?
The oil ring is the lower ring that helps lubricate the cylinder wall while simultaneously preventing excess lubricant from entering the cylinder.
How do the pistons on a reciprocating compressor work?
The reciprocating motion of the piston moves the pistons up and down in the cylinders to draw in and compress the refrigerant before sending it out the exhaust valves to the discharge line.
What is the most common failure point on a compressor?
The shaft seal
What determines the speed of a belt-driven compressor?
The size of the compressor pulley in relation to the size of the motor pulley
Why is the motor and compressor spring mounted in a hermetic compressor?
The spring mounting prevents most of the compressor vibration from being felt outside of the dome.
How is the motor connected to the compressor in a hermetic compressor?
They have a shared shaft
What are the three advantages of the rotating-vane rotary compressor?
They provide large opening into the suction line They provide large inlet port openings They have a very small clearance volume
What will happen if the two rubbing surfaces on the shaft seal are not lubricated?
They will wear and allow leakage to occur
How does a scroll compressor can remove any liquid?
Through axial movement and bleed holes
What is another term given to fully hermetic compressors?
Throw-away hermetic compressor
What is the viscosity rating used for?
To indicate the fluid's ability to flow at a given temp
Why does a rotary compressor use a check valve in the discharge line?
To prevent back flow of refrigerant during off cycle
T/F: Fully hermetic compressors cannot be serviced in the field without cutting open the shell.
True
T/F: Pistons rings are not used in some small compressors.
True
T/F: Shaft seals are not required for hermetic compressors.
True
T/F: The pulleys on a belt-driven compressor must be in perfect-alignment, have proper tension, and motor/compressor shafts must be exactly parallel to each other.
True
T/F: heat pumps have crankcase heaters but most residential split systems do not
True
T/F: in hermetic systems, the pistons and rings are constructed much the same as those used in the open-drive compressors only smaller in diameter and lightweight.
True
T/F: the pressure lubricating system is more efficient than the splash method
True
A mechanism that temporarily reduces the pressure in the compressor during startup is called ______.
Unloader
_______ is a fluids resistance to flow
Viscosity
What is required to prevent leaks on an open-drive compressor?
a shaft seal is required where the shaft comes through the compressor case.
What applications are scroll compressors used?
air conditioning heat pumps
How are semi-hermetic compressors usually cooled?
air cooled and have cooling fins on the exterior housing to increase surface area for improved heat dissipation
What are cylinders?
bores (holes) in the cylinder block, within which the cylinders move up and down.
How are hermetic motor lubricated?
by oil carried in the refrigerant
How are hermetic compressors lubricated?
by the oil in the refrigerant as it flows through the unit
What are compressor cylinders typically made of?
cast iron
What are the two types of piston rings called?
compression ring oil ring
What does the connecting rod do?
connects the piston to the crankshaft
What are the parts that make up a reciprocating compressor?
crankshaft connecting rods w/wrist pins pistons cylinders intake and exhaust valves
How are the shafts connected between the motor and compressor in a direct-drive compressor?
end to end
What is another name for open-drive compressor?
external-drive compressor
What is used between the bolted parts of a semi-hermetic compressor to prevent leaks?
gaskets
What are the rubbing surfaces of the shaft seal made of?
hardened steal and bronze or ceramics and carbon
What are the three architectural designs for a compressor?
hermetic compressor semi-hermetic compressor open-drive compressor
What are compressors that include an integrated drive motor in a sealed unit called?
hermetic compressors
What is the major concern for open-drive compressors?
keeping the refrigerant sealed within the system
What are the primary concerns when selecting a compressor for residential and domestic applications?
noise and serviceability
list the toes of compressor cooling systems
oil circulating in compressor air-cooled (fan and condenser coil) water-cooled (circulating water outside unit)
where are compressor service valves used?
on most open-drive compressors and some hermetic compressors
What three factors are used to determine the type of compressor needed for a given application?
physical size of the unit cooling capacity required cost, servicability noise requirements
What are the primary concerns when selecting a compressor for commercial air conditioning?
serviceability and easy access
What is another term for semi-hermetic compressor?
serviceable hermetic compressor
What do the crankshaft main bearings do?
support the crankshaft provide low-friction surface for it to rest on as it rotates carries the load applied to the crankshaft
In small compressors that do not have piston rings, how is the seal created around the piston?
the piston in a small compressor has oil groves cut in them which fill with oil and create a seal between the piston skirt and the cylinder wall
What is the crankshaft used for?
to change rotary (circular) motion into reciprocating (back and forth) motion
What are piston pins used for?
to connect the piston to the connecting rod.
In a fully hermetic compressor, what position is the motor and compressor shaft in?
vertical position
