Compressors Flashcards
In pneumatic compressors what is more valuable, volume or pressure?
Volume
What is the common unit used with pneumatic compressors?
CFM = cubic feet per minute
What does CFM stand for?
Cubic Feet per minute
What creates pressure in a pneumatic compressor system?
Resistance to flow = pressure
What do all compressors have for a safety?
Relief valve
What causes the high cost of running compressors?
Leaks
What are pneumatic compressors designed to do?
Increase the pressure of air by reducing its volume
What are the two sides to a compressed air system?
Supply and Demand
What is the difference between a hydraulic system and a pneumatic compressor system?
The air does not return to tank
What should you ALWAYS do with a pneumatic system prior to working on it?
Bleed off pressure
What is the benefit of adding a second compressor to a system?
Minimize pressure drops
What are the two terms for two compressors in a system
Master/slave
Load/lag
What are the benefits of using a load/lag compressor system
Different cut in/out so not working all the time
Easier maintenance
What type of compressor is on all the time but can throttle down as required?
Screw compressor
How large should a dryer system be on a compressor?
Large enough to handle the max pressure your system can contain
What does an air dryer do in a compressor system?
Removes water/condensation
Why do we need to remove water from an air system?
Prevent freezing
Prevent oxidation/corrosion
What does FRL stand for?
Filter
Regulate
Lubricate
What type of compressor typically does NOT have a tank?
Screw compressor
What will drop a temperature in an air system?
Higher flow rate
What would frost on a system indicate?
Too high of flow
In a compressor system how are pressure and volume related?
They must be balanced for the system to work correctly
What are the 2 principal operations of a compressor?
Dynamic
Positive displacement
When would dynamic compressor systems be favoured over positive displacement systems?
Large volumes
Low pressure (>100psi)
When would a positive displacement compressor system be favoured over a dynamic system?
Moderate volume
High pressures ( <100psi)
What are the 2 types of motion from a positive displacement compressor system?
Reciprocating
Rotary
What are the 3 most common rotary positive displacement compressors?
Vane
Lobe
Screw
What is another name for a dynamic rotary compressor?
Centrifugal
What parameters do larger compressor typically need prior to fully starting a system?
Oil temperature
Oil pressure
Air pressure
What must a relief valve on a compressor be sized for?
Release of the max volume produced by the compressor
Why are compressor outlets typically fitted with check valves?
To prevent back feeding
What is a maximum pressure control?
Way to prevent over pressurizing
Unloading device allowing the least hp demand when at max pressure
What are “fingers”
Unloading device
What do “fingers” do?
Hold intake valves open when max pressure is reached
What are the methods of controlling max air from a compressor?
Throttling air intake
Using variable speed drive
Using a pressure switch to start/stop motor
What does staging compressors do?
Create higher pressure
When setting a pressure switch what do you typically want to do with your stop and start points?
Add a buffer so the system is constantly kicking on and off
If you have a single adjustment switch what are you adjusting?
The stop point NOT the start
What are the two types of centrifugal compressors?
Vane
Impeller
In a compressor system what is velocity energy changed into?
Pressure energy
What psi are centrifugal compressors capable of?
Between 100-10,000psi
What is an example of an axial compressor?
Gas Turbine
Where does the working fluid flow on an axial compressor?
Parallel of the axis
What type of flow does an axial compressor produce?
Continuous flow
If you want an axial compressor to produce larger pressures what does it require?
More aerofoil
What is the difference between gas turbines (GT) and Steam turbines (ST)?
The direction of flow is reversed
(Gas compresses through the turbine, steam expands)
What is the typical reduction ratio to each stage of an axial compressor?
2:1
If a 2 stage compressor has 1 impeller on each side how many thrust bearing would it require?
Only 1
On a 2 stage impeller compressor where there is 1 impeller on each side how would you know which end to put the thrust washer?
Dependant on the direction of rotation
How are impellers typically installed?
Keys
Set screws
Threaded
Typically on a threaded impeller what direction are the threads
Left hand depending on rotation
Why are the keys on an impeller typically a soft metal?
To protect the impeller
How can you adjust output rate on dynamic compressors?
Rpm
Fin shape
Changing input/output ports
How does a balance piston create a seal?
By using the pressure of the compressor
What does a dry seal mean?
There is no oil involved
What is a thrust collar?
Another support which acts similar to a bearing
How does a back to back impeller arrangement sharing a discharge stay balanced?
By having the same flow paths
Why would it be important for a back to back impeller arrangement to have balanced paths?
To prevent back flow
How do labyrinth seals work?
By using close tolerances to reduce pressure
What are carbon seals?
Another sealing mechanism
Similar to labyrinth seals
How are mechanical seals typically attached to a compressor?
With set screws or springs
What is typically doing the sealing work in a mechanical seal on a compressor?
O-rings
Why is lubrication more vital in multistage compressors?
Multi stage = higher pressure = higher heat output
If you have an increase in pressure how will this affect temperature?
It will raise
What is a beam?
A rotor being supported by bearings at both ends
How are antifriction bearings typically lubricated in a compressor?
Oil bath
Feeder
How is a plain journal bearing typically lubricated in a compressor system?
Oil bath
Ring
Chain
What is an oil dam?
A sheet of metal that stops oil from missing components and redirects it to where it’s needed
What lubrication systems will you typically see and oil dam?
Ring
Chain
Describe pre lube/jacking oil
Prior to starting it creates an oil film between journals
What type of equipment would you typically see pre lube/jacking oil systems?
Heavy equipment
Where should an intake for a compressor ideally be located?
Higher up for less moisture
What are the 3 main components to an axial compressor?
Rotor
Stator
Casing
What is peening in terms of axial compressors?
Expanding the metal at the root of a disc to prevent it from moving
What are the two types of rotors in an axial compressor?
Drum
Disc
What are drums in terms of axial compressors?
Discs that are flanged to fit each other and held together with tie bolts
What are discs in terms of axial compressors?
Individual rotor discs mounted onto the rotor shaft
How are rotor discs blades attached?
Fir tree
Dove tail
Bulb type
In reciprocating compressors if there is 4 pistons that are the same size is it staged?
NO
How is the ratio of a reciprocating staged compressor determined
the physical difference (volume) of the pistons
For a reciprocating compressor to have multiple pistons but still be single staged what is required?
For all pistons to be the same size
Where is an inter cooler located on a compressor?
Between stages
What compressor design has a piston but no piston rings?
Labyrinth
How many compression strokes are there for every rotation of the crankshaft in a double acting compressor
Two
Why is it common for compressors with high compression ratios to be liquidly cooled
Due to the excess heat generated
A pressure differential causes what component on a pump to open and close?
The valve
What is the primary function of the distance piece?
To prevent contamination between oil and gases
What is the purpose of vanes in a compressor system?
To change airflow through the compressor
What is a surge in terms of compressors?
Minor instruction to airflow
Minor interception to airflow can also be called what?
Surge
What is the purpose of the fins on a cooler?
To provide more surface area for better cooling
What way do you put piston rings in?
With the dots facing up
What direction should the dots be on a piston ring?
Facing up to
What is a cross head in a compressor?
The component that slides on the rod to provide stability and centre the piston rod
What is the purpose of a cross head in a compressor?
To provide stability and centre the piston rod
What type of compressor typically requires a crosshead?
Larger compressors
How many cross heads would be required on a large compressor with two independent piston rods?
2 (one for each rod)
Why do we want the pressure to be relieved in a compressor when it is shutdown
To minimize wear on components
What does a tandem cylinder arrangement mean?
Side by side
Why is timing critical in tandem cylinder arranged compressors?
To ensure the cylinders don’t fight each other
(Prevent back feeding)
What do unloaders do in compressors?
Manipulate the suction valves
What are clearance pocket valves for?
Altering the cylinder head space
What would a valve that alters the cylinder head space of a compressor be called?
Clearance pocket valve
What is another name for a distance piece?
Dog house
What do packing rings do on a cylinder inside a compressor?
Contain the gas pressure and prevent oil from entering the cylinder
Is the distance piece typically vented?
Yes
What is the main components in a running gear compressor?
Crosshead
Connecting rod
Piston rod
Crankshaft
What is a crankshaft?
A shaft with counter weights that balance the dynamic forces caused by the pistons
How are crankshafts typically supported?
With plain and journal bearings
What restores rotational inertia and adds mechanical advantage inside a compressor?
Flywheel
If a compressor is oil-less how is it lubricated?
By using self lubricating parts
What are examples of materials that can be found inside an oil-less compressor?
Teflon
Plastics
Graphite
Why would a gas be preheated before entering a compression system?
To turn it into a vapour phase
What component in a compressor system can also act as an accumulator
Reservoir (tank)
What type of speeds can you expect from MOST reciprocating compressors
Relatively low
How are reciprocating compressors typically driven?
Directly or by belts
What can be used to manipulate the speed of a reciprocating compressor?
Gear box
Pulleys
Are vane compressors typically considered dynamic or positive displacement?
Positive displacement
Is the volume of a vane compressors typically considered variable?
No
Can vane compressors be oil-less?
Yes depending on vane material
Are vane compressors manually adjustable?
Self adjusting
Where can an oil release valve be found?
At the bottom of the impeller housing.
What is the purpose of an oil release valve?
To prevent hydraulic lock
Redirect oil to the tank when compressor is not in use
What are anodes?
Corrosion pieces
What is the purpose of an anode?
To be a sacrificial piece
Redirect corrosion to itself
What are the 3 most common materials used for anodes?
Aluminum
Zinc
Magnesium
Can a vane compressor be used to pull a vacuum?
Yes
What material would you use for an anode in a salt water system?
Zinc
What material would you use for an anode in a fresh water system?
Magnesium
Can vaccums be stagged?
Yes
What is the purpose of a seperator?
Separate oil from air
What component will remove oil from air?
A seperator
What is the purpose of a minimum pressure valve?
To ensure oil circulation system is satisfied prior to sending air into the system
How are vane tips sealed in a wet compressor?
Centrifugal forces and oil
What are the components in an automatic air control system?
Servo
Unloader valve
Where can an oil relief valve be found?
Typically at the top of the impellar housing
What is the purpose of an oil relief valve?
To relieve oil trapped in the impeller of the compressor while running
Prevent hydraulic lock
What type of unloading pressure does an oil relief valve have?
Cracking pressure
How do oil release valves stay closed during operation?
Using the sump air pressure
What is the main purpose of a cooler by pass valve?
To increase oil temperatures quickly
What is the secondary purpose to a cooler bypass valve?
To act as a safety for a blocked cooler
Where can a vacuum relief valve be found on a compressor system?
Within rotor area
Is a lobe or root blower a compressor?
No
Does a lobe blower require timing gears?
Yes
Can a lobe blower be used to crate a vacuum?
Yes
Where would skip be in a lobe blower?
Around any clearances
What does adding more lobes to a blower system do?
Increases efficiency
What is a helical lobe blower?
A mix between screw and lobe pump
Does oil resviour orientation matter?
Yes
Can you alter a screw compressors flow?
No
What are the two basic types of screw compressors?
Single rotor
Dual rotor
How can you increase pressure in a screw compressor?
Staging
How many rotors are driven in a dual screw compressor?
1
Can a screw compressor be oiled or oil-less?
Both
How is the pressure ratio determined on a screw compressor?
By the location of the discharge port
