Modern Chap 19/20 Flashcards
Compressors are driven by an ______ motor
electric
Compressors that are driven by an external motor are called ___________ compressors
open drive
compressors that are driven by an integrated motor are called _________ compressors
hermetic
There are two ways of joining a motor to an open drive compressor ______ drive and _____ driven
direct drive and belt driven
A direct drive compressor is driven by a _______ connecting the shaft of an electric motor directly to the compressor shaft
coupling
On a _________ compressor, a belt connects a pulley on the drive motor to a pulley on the compressor shaft
belt driven
On most compressors, the compressor pulley is larger than the ______ pulley which causes the compressor to turn more slowly than the motor
motor
Refrigeration compressors can also be driven by ________________ engines
internal combustion
Fully hermetic compressors are built in sizes from ____hp to ___hp
1/6hp to 20hp
A ______ ring is a split metal ring that is installed in a groove that encircles the piston
piston
Name the two types of piston rings;
compression rings and oil rings
Upper piston rings are known as compression rings, their purpose is to prevent pressurized _________ from blowing past the piston
refrigerant
The lower oil ring is designed to help ________ the cylinder wall while simultaneously preventing excess lubricant from entering the cylinder
lubricate
__________ are metal cylinders that connect the pistons to the connecting rods
piston pins
Compressor cylinders are usually made of
cast iron
As the piston moves down it creates a ______
vacuum
Although the refrigerant in the intake manifold is at a low pressure, it is still a greater pressure than the _______ in the cylinder when the piston is moving down
vacuum
As the piston moves upward in the cylinder, the increased pressure ______ the intake valve
seals
Poppet valves are only suitable for ____ speed compressors because they operate slowly
low speed
The _______ head serves as a pressure plate, sealing the top of the cylinder so the refrigerant can be compressed
cylinder head
A cylinder head also provides ______ passages into and out of the compressor
vapour
The portion of the compressor housing that supports the crankshaft is called the _______
crankcase
The portion of the housing that contains the cylinders is generally called the ________ block
cylinder
Adding more cylinders increases the _______ capacity for each revolution of the crankshaft
pumping
Compressors can have from one to _____ cylinders
twelve
Name some different cylinder arrangements:
Vertical, V, X, Y, Z, or radial
In a ________ design there is no connecting rod
scotch yoke
Scotch yoke is popular in _____ high ______ compressors
small high speed
In a scotch yoke design the piston and cylinder are _____
long
A rotary compressor is a compressor in which vapour compression takes place in spaces between the __________ and sides of an off-centre rotor that spins inside the cylinder
cylinder wall
A _______________________ compressor uses an off centre rotor to turn vanes(blades) that create pickets between the rotor and cylinder wall
rotating-vane rotary compressor
In a rotating vane rotary compressor, the low pressure vapour from the suction line is drawn into the opening between vanes as the vanes revolve. The trapped vapour in the slace is compressed until it can be pushed into the ___________
discharge/exhaust line
_______ compressor is the name commonly given to the first compressor in a cascade system
booster
Rotating vane compressors are frequently used as the booster compressor in a _________ system
cascade
In a stationary-blade rotary compressor the blade is stationary instead of the _______ like in a rotary vane
rotor
A ______ compressor produces vapour compression between the walls of a fixed scroll and an orbiting scroll
scroll
As two high-pressure pockets are discharging, new low-pressure pockets are formed at the outer edges of the _____
scroll
The suction from the outer portion of the scroll and the discharge from the inner portion are ________
continuous
In a screw compressor the male rotor has ____ lobes and the female has ____ interlobe spaces
male 4
female 6
In a screw compressor the ______ rotor meshes with and drives the male rotor
female
In a screw compressor the male rotor rotates ____% faster than the female rotor because they’re are four lobes on the male rotor and six meshing grooves
50%
Unloader mechanisms provide a unique feature of screw compressors: their ability to control capacity through _______ _________ unloading which allows for smooth accurate control
infinitely variable
A _________ compressor is a compressor consisting of a rotor operated impeller with radial blades inside a volute casing
centrifugal
The force that throws the vapour outward during the impeller stage is called
centrifugal force
Centrifugal compressors are more efficient when operating at ____ speeds and are designed to be
high
The ______ in a centrifugal compressor is the casing in which the impeller rotates
stator
The stator is a volute design meaning that it is _______ shaped
spiral
There is no vapour trapping pockets in a _________ compressor
centrifugal
How to attach gauges when there are no service valves?
use special tapping valves that pierce the lines
_________ reduce noise that may be caused by gas pulsation
mufflers
The heat must be removed from a compressor to prevent loss of ________ and to maintain the lubricating qualities of the oil
efficiency
_______ is a fluids resistance to flowing
viscosity
______ oils have a viscosity that is best for refrigeration temperatures and refrigerant
mineral
Reciprocating compressors may be lubricated by either a ______ or ________ (force feed) system
splash or pressure
In the _____ system, the crankcase is filled with the correct oil up to the bottom of the main bearings or to the middle of the crankshaft bearing. Each revolution the crank throw is dipped and splashes oil everywhere
splash system
_________ lubrications systems use a small oil pump to force oil to the main bearings.
pressure
Since the oil pump delivers oil, under pressure, to all bearing surfaces, a _______________ system provides better protection than splash
pressure lubrication
An _________ is a mechanism that temporarily reduces the pressure in the compressor during start up
unloader
An unloader may be operated ; (3)
electrically , mechanically, or hydraulically
An unloader may also be used to vary the ________ capacity in certain compressors wbu h is useful when there is a changing heat load like an air conditioner
pumping
_______ devices are used throughout the compressor wherever a gap between components puke allow refrigerant or pressure to escape
sealing
Name three types of sealing devices
gaskets , O rings, shaft seals
On open drive and semi hermetic compressors, mating surfaces of the cases are usually sealed with ______
gaskets
O rings are used when there may be some ______ between the assembled parts
motion
A _______________ is a device that warms up the compressor crankcase to evaporate any liquid refrigerant trapped in the oil
crankcase heater
During the off cycle, refrigerant will migrate to the coolest part of the system which is the
compressor
Crankcase heaters may be operated during the off cycle or they may be ____________ controlled
thermostatically
Crankcase heaters are required on compressors that operate in ambient temperatures ______ than the _________ temperatures
lower than the evaporator temperatures
If the refrigerant gets to the compressor and condenses then the ref/oil mix will begin to foam when the compressor starts. This causes the oil charge to pump out of the compressor , a condition know as ________
oil slugging
Slugging of oil or liquid refrigerant can cause ; (3)
broken valves, damaged pistons, and broken head gaskets
A heating coil keeps the crankcase coil up to ___ degrees warmer than system temperature to ensure the oil will be warm enough to mix with refrigerant and prevent _________
30F warmer
prevent oil slugging
Which is the most expensive; compressor, condenser, evaporator, metering device?
compressor
______ slugging can damage compressor valves, pistons, scrolls, and vanes
liquid
All mechanical compressors require two basic elements; ______ oil for lubrication and _____ free vapour refrigerant for cooling
clean oil and liquid free vapour refrigerant
Name three safety devices that ensure compressors do not run during periods of excessive heat or pressure?
internal overloads, external overloads, pressure switches
What are some important variables that a safety device may monitor;
- Current draw on compressor motor
- temp of the discharge line
- head pressure
- temp of compressor dome
Motors and other current drawing electrical devices require __________ protection
overcurrent
______ current can damage conductor insulation and lead to a short circuit or a ground fault
high current
How is overcurrent protection provided?
circuit breaker or fuses
A ________ overload is a type of diodes or protection device that is mounted to the compressor shell near the compressor motor terminals
thermal overload
thermal overloads use a bimetal disc that opens and closes a set of electrical contacts based on ________
temperature
Where are internal overloads located in a compressor?
wired into the motor windings at the manufacturer
What is a CPR?
crankcase pressure regulator
what is LRA?
locked rotor amperage
A ______________ regulator is a valve with an adjustable pressure setting that prevents crankcase pressure from exceeding preset safe value
crankcase pressure regulator
Where is a discharge pressure switch installed? between the ________ and the __________
compressor and the condenser
What is a discharge line pressure switch?
shuts compressor off if head pressure gets too high
Another way to protect against high discharge pressure is a discharge line ________
thermostat
A _______line ________ senses discharge line temperature and opens on a rise in temperature to turn off the system and protect the compressor
discharge line thermostat
An accumulator consists of a tank with a reservoir on the bottom for __________ refrigerant and an inlet and outlet on top for the flow of _________ refrigerant
liquid refrigerant
vapour refrigerant
An ____ separator is a system component that removes oil from high pressure refrigerant vapour as both refrigerant and oil leave the compressor
oil
An oil separator is placed in the _______ line between the compressor and condenser
discharge line
An ___ reservoir is a storage vessel that holds an oil supply for a compressor or a group of compressors
oil
Oil trapped by the _____________ is returned to the oil reservoir until it is needed
oil separator
An ____ ______ regulator is an oil control device that regulates the level of oil within a compressor using a float mechanism
oil level regulator
What happens when the float drops in an oil level regulator?
oil level is low so the regulator opens to allow oil to flow from the reservoir
oil _______ control is a form of control that will shut off electrical power to the compressor of the net oil pressure or oil level drops beeline normal for a certain amount of time
safety
A __________ absorber is a flexible line of tubing that carries refrigerant but also reduces or dampens any vibration or physical motion
vibration
Vibration absorbers should be installed in both the _______ line and ________ line as close to the compressor as possible
suction line and discharge line
