Compressors Flashcards
What are the 3 Drive types
- Open Drive Compressor
- Hermetic Compressor
- Semi Hermetic Compressor
Types of compressors
- Reciprocating
- Scroll
- Rotary (rotating vayne and stationary blade)
- Screw
- Centrifugal
How much oil can compressor lose upon start up ?
5-7%
What is the maximum discharge temp for compressors ?
225 farenheight
5 tons and below are “usually” what types of compressors ?
Reciprocating, rotary and scroll
10-100 tons are “usually” what ?
Reciprocating and Screw
Over 100 tons are usually what type of compressor ?
Centrifugal
Types of open drive compressors
- Belt drive
- Direct Drive
What do open drive compressors have that other typically don’t require ?
Shaft seal because the crankshaft extends through the compressor body so it can connect to the drive motor
In what types of equipment are rotary compressors commonly found ?
Small refrigeration appliances
What is the purpose of a shaft seal on open drive compressors?
Shaft seal is designed to prevent leaks and can withstand varying pressures. Seal must be lubricated and is a common failure point.
How are hermetic compressors cooled ?
Typically suction cooled
Can be cooled via air and water
Are semi hermetic compressors serviceable?
Yes, they are enclosed in a bolt assembly
Why do hermetic compressors have a greater pumping capacity ?
How are they lubricated?
Because they run at a higher RPM.
Lubricated by oil in the refrigerant.
What are the types of crankshafts for reciprocating compressors?
- Eccentric type
- Crank throw type
- Scotch yoke
Valve types ?
- Reed valve
- Poppet valve
- Discuss valve
- Ring valve
What applications are reciprocating compressors used for ?
- Domestic
- Commercial
- Industrial
(Highly versatile)
In what compressor(s) is a check valve installed on the discharge side of the compressor to prevent equalization in the off cycle ?
Rotary compressor, scroll compressor
Common applications for scroll compressors ?
Residential, commercial air conditioning/heat pump applications
Benefits of a scroll compressor ?
Fewer moving parts, less internal friction, smooth compression cycle
Which compressor has no internal suction valve ?
Scroll
How does a screw compressor work?
Helical rotors compress refrigerant Vapor.
Male rotor has 4 lobes.
Female rotor drives male rotor
Which compressor uses oil injection and why ?
Screw compressor
To provide a seal to prevent leaks and help cool the compressor.
Why do screw compressor typically have lower discharge temperatures ?
Because of the large amounts of oil used for lubrication.
Lower compression rate = what ?
The more efficient and cooler the compressor will operation
How does a suction valve open ?
How does a discharge valve open ?
1.When the volumetric pressure decreases inside the compressor chamber
2. When the volumetric pressure increases inside the compressor chamber
What do connecting rods do ?
- Connect the piston to the crankshaft
- Bearing provide low friction surface
Connecting rods for crank throw crankshaft ?
Split end clamps around journal or crank throw
Connecting rods for crank throw crankshaft ?
Split end clamps around journal or crank throw
Connecting rods for eccentric crankshaft ?
End is solid ring
Non positive displacement compressor ?
Centrifugal chiller
How many impellers do centrifugal have and what is the rpm range ?
1-4 impellers that rotate between 3000-20,000 RPM.
Purpose of crankcase heaters?
Warms compressors crankcase, evaporates liquid refrigerant trapped in oil
How do centrifugal chillers work?
- Vapor is fed into the casing (stator) in the Center.
- Impeller spins rapidly in the casing.
- Centrifugal force throws Vapor outward causing compression.
What is the stator in a chiller ?
Casing in which impeller rotates.
Volute design (spiral)
What is the stator in a chiller ?
Casing in which impeller rotates.
Volute design (spiral)
Impeller in a centrifugal chiller ?
Keyed to compressor shaft.
No Vapor-trapping pockets.
Designed to move more Vapor’s without going above gas velocity limits
Which reciprocating compressor crankshaft has no connecting rod ?
Scotch yoke
Types of piston rings
- Upper rings (compression rings)
Prevent pressurized refrigerant from blowing past the piston into the crankcase - Lower ring (oil ring)
Helps lubricated the cylinder wall while simultaneously preventing excess lubricant from entering the cylinder.
Poppet valves are only suitable for what speed compressors ?
Low speed since they move slowly
What serves as a pressure plate, sealing the top of the cylinder so that the refrigerant can be compressed ?
Cylinder Head
What reduces noise that may be caused by gas pulsation ?
Muffler
Brazed cylinders with baffle plates mounted inside and allows the gas to expand “smooth the flow”
What are “O” rings commonly used for ?
Used as sealing devices, especially where there may be some motion between the assembled parts.
What is an “unloader”
Mechanism that temporarily reduces the pressure in the compressor during start up.
What is the purpose of oil failure control ?
Shuts off the compressor if oil is not being circulated properly.
(Understand how it works/wired)
