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123 Cards in this Set
- Front
- Back
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0°k in °c |
-273°C |
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2 properties of all fluids |
1.Pressure difference required for flow 2.Always flows from high pressure to low |
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2 Properties unique to gasses |
1. Gasses can be compressed 2. Gasses fill the container they are in |
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Ways to increase pressure of a sealed system |
1. Reduce volume 2. Increase temperature 3. pack more gas in the container |
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0°R in °F |
-460°F |
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Atmospheric pressure at sea level in psia,kPA,and bar |
24.7 psia 101.43 kPa 1.01 bar |
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Pressure at 0°K/0°R |
0 psia -14.7 psig |
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Types of gauges for compressed gas systems |
Vacuum scale Gauge pressure scale Absolute pressure scale Combination vac/gauge scale |
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Common devices for measuring pressure |
Barometer Manometer Bourdon tube |
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What can a barometer measure |
Both vacuum and pressure |
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How tall is the mercury in a barometer at sea level |
29.92 inches(760 mm) |
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How much does the mercury move per 1000' in altitude gained and what direction |
It drops 1" per 1000' rise in elevation |
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What is the most accurate means of measuring a vacuum. |
Manometer |
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How far would the water have to move in a manometer to read 1psi change |
2 feet |
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Of barometers, nanometers, and bourdon tubes what is the least accurate and why? |
Bourdon tubes are not as accurate because of the mechanism involved |
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What law states that pressure applied to a confined or static fluid is transmitted equally in all directions and what direction is the pressure being transmitted |
Pascal's law. It also states that the pressure is being transmitted at 90° angle to the surface. |
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What is the difference between Pascal's law and Bernoulli's principle |
Pascal's deals with non moving fluid and Bernoulli's principle deals with a constant flow of fluid. |
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What is Bernoulli's principal |
Velocity (kinetic) increases as pressure (potential) decreases. |
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4 gas laws |
Boyle's law Charles' law Gay-lussac's law Combined gas law |
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Boyle's law |
Volume decreases 2x = pressure increases 2x |
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Charles' law |
Volume changes proportional to absolute temperature Temp X2 = volume x2 |
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Gay-lussac's law |
Pressure in a fixed volume increases proportional to the absolute heat °k *2 = psia *2 |
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Combined gas law |
(P¹*V¹)/T¹= (P²*V²)/T² |
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What are the effects of altitude |
Decrease in atmospheric pressure Air gets thinner |
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Effects of altitude on compressors |
Decrease in power requirements/decrease in air flow |
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Effects of moisture on compressors |
Freezing in below freezing in temps Rust equipment/lines causing blockages Some applications are hard by moisture Harmful to lunricants |
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Types of reciprocating positive displacement compressors |
Single acting Double acting Labyrinth Diaphram |
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Types of rotary& screw positive displacement compressors |
Rotary: Sliding vane Liquid ring Screw: Single rotor Two rotor |
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Single acting compressor |
Only compresses on one side of the piston |
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Double-acting |
Compresses on both sides of the piston |
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Labyrinth compressors |
Create seal between the cylinder and piston with a series of matching groves More internal leakage but oil free air |
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Diaphragm compressors |
Flexible membrane attached to con rod in place of piston low flow rate moderate pressure and vacuum service only Hydraulic diaphragm compressors use hydraulic pressure in place of the con rod |
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Integral compressors |
Internal combustion engine with spare pistons for compressing gasses. |
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Reciprocating compressor components |
Frame Crankshaft Connecting rod Crosshead and guides Pistons Cylinders Valves Distance pieces |
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What houses the major parts of the compressor |
Frame |
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What turns rotary motion into reciprocating motion |
Crankshaft |
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Where is the connecting rod connected on Both double and single acting compressors |
Crankshaft/piston on single action Crankshaft/crosshead |
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What keeps the piston rod centered through the packing |
Crosshead and guides |
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What compresses gas on both sides and what are they connected to |
Double acting pistons are connected to the cross head through the piston rod |
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What compressor type has pistons similar to power pistons in industrial engines |
Single acting compressors |
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What is the difference in the cooling of the cylinders of low pressure vs high pressure systems often have |
Low pressure is air cooled High pressure is water cooled |
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What are valves designed to do |
Control the flow of gas in and out of the cylinder |
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How do compressor valves differ from common engine valves? |
They open and close due to pressure changes |
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What prevents the contamination between the cylinder gas and oil |
The distance piece. |
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Where does the distance piece fit |
Between the cylinder and the main frame |
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Where is the vent and drain connection located and what is it used for |
It is located on the distance piece and it is used so that leaking oil and gas can be routed to a safe location |
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Every effort should be made to remove what before it gets to the compressor |
Abrasive particles Corrosive gasses Liquids |
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What are some common filters |
Paper Oil bath Cyclones Scrubbers |
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Where should the intake system be located to ensure the compressor is most efficient |
As cool as possible because colder air is denser. |
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How should piping be sized |
Large enough and with as few bends as possible to minimize pressure drop |
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What is laminar flow |
Flow in a straight line |
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What is turbulent flow |
Flow other than in a straight line. |
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What do sharp bends cause |
Friction Turbulence Resistance to flow Pressure drop |
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How do you combat turbulence. |
Smooth surface with large radius bends and sufficient size |
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What happens when the pipes natural frequency matches compressor frequency and how to fix it |
Disturbing noises and stress to the pipes/machine Change the length of the pipe to fix. |
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Why are compressors unloaded on startup |
Reduce starting torque and prevent damage. |
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How do reciprocating compressors accomplish unloading during startup. |
Holding open the suction valves |
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What is considered a small compressor |
10hp and lower |
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How are small compressors designed to start and stop |
Simple pressure switch |
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What are some ways large compressors are controlled |
Start/stop Inlet valve unloading Variable speed Bypass Variable volume pocket |
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Why don't large compressors use a pressure switch |
The compression force is too great requiring the compressor to be overpowered. |
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How do large compressors function with no pressure switch |
They run continuosly and have inlet unloading or bypass. They will sometimes have a timer to shut off if run unloaded for too long. |
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Why do large compressors sometimes have a timer shutoff after too long unloaded |
Increase in valve temperature causes wear |
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What is an intercooler |
Heat exchanger used to cook compressed gas between stages |
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How much do intercoolers decrease power requirements |
15% |
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What is an aftercooler used for |
Remove moisture after compression is complete |
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How do dryers get rid of moisture |
Dropping the dew point or absorbing the moisture |
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What kind of dryer is filled with a chemical that melts as it absorbes water? |
Deliquescent dryer |
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What is one major problem of a deliquescent dryer |
The chemicals are corrosive when mixed with water |
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What dryer reduced the dew point to just above freezing |
Refrigeration dryers |
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What are some mechanical dryers |
Cyclone separator Filter |
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What are air receivers used for? |
Store compressed air allowing for fluctuations in demand and the system pressure to fluctuate within limits |
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Can you weld on pressure vessels? |
They must be pressure welded |
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What code is enforced for receivers? |
Alberta boiler and pressure vessels act |
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Why are safety relief valves needed |
To protect the compressor and other parts of the system |
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Where must safety relief valves be installed? |
Each component in a compressed air system and between the compressor and anywhere there is a possibility of obstruction. |
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What is a FLR |
Filter lubricator regulator |
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What is the FLR used for |
To condition the air and rid it of contaminants, adjust the pressure , and add/remove oil |
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What can cause contaminants in the air system |
Construction assembly or maintenance Oil and wear particles from the compressor Pipe scale and rust forming inside the system |
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Why use a regulator? |
Reduce pressure coming from the system. |
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Why have Oilers |
Many pneumatic components required a controlled amount of clean oil to lubricate cool and seal effectively |
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What are water traps used for |
To remove large amounts of water from the system |
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When should water traps be installed? |
When the air is allowed to cool below its dew point the moisture drops out. If the moisture can cause damage to components a water trap should be installed. |
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Cfm |
Cubic feet per minute |
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Scfm |
Standard cubic feet per minute |
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Mmscfd |
Million standard cubic feet per day |
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In³/m |
Cubic inches per minute |
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M³/m |
Cubic meters per minute |
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How is capacity stated on most compressors |
Free air delivered (fad) |
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What does free air delivered mean |
Free air means the free air supply available to the intake Delivered refers to the volume of air delivered at the rated discharge pressure |
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Why is free air delivered a better way to rate compressors versus air drawn into the compressor |
fad takes into account internal leakages and is more accurate |
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What is pressure ratio |
Ratio of absolute discharge compared to absolute intake pressure. |
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What does excessive pressure ratio cause |
Extreme temperature Excessive rod loading |
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What are pressure ratios normally limited to |
5:1 |
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What if you need higher than normal pressure ratio |
You have 2 stages working equally to step up the ratio (9:1 needed = 3:1 first 3:1 second) |
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What is volumetric efficiency |
Ratio of the actual compressor capacity compared to the calculated displacement |
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What is the swept volume |
The volume of air swept or pushed out of the cylinder on the compression stroke. |
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What is clearance volume |
The space between the piston and cylinder head at TDC |
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What happens if clearance volume is too high |
The gas has to expand back to atmospheric pressure before it can take in more air lowering efficiency |
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According to the compressor industry what is a SCF of gas |
One cubic foot of gas at 68°f 14.7psia and 36%RH |
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According to the gas transmission industry what is one standard cubic foot of gas |
One cubic foot of gas at 60°f 14.7psia and 36% RH |
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What is staging |
Single stage uses compression uses one compressor Mulit stage has multiple compressors in line to compress from initial to final compression ratio |
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Single action compressor |
Compression occurs on one side of the piston One stroke per revolution |
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Double acting compressors |
Compression occurs on both sides of the piston. 2 strokes per revolution |
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What must be done before working on a compressed air system |
Venting (release pressure) |
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What is purging and why? |
Filling the compressed gas system with gas that is not dangerous to work around/in |
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What are clearance pockets used for |
To reduce capacity by increasing the clearance volume |
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What is rod loading |
Sum of the suction and discharge pressures acting in a double acting compressor. Rod loading needs to be kept within limits |
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Rod reversal |
Recip compressor term that has to do with alternate compression and tension forces of the piston rod during operation |
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What is rod reversal necessary for |
To allow oil to flood around crosshead pin and connecting rod pin bushing |
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What is the largest factor in compressor efficiency |
Compressor valves not operating properly |
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What are some forces that compressor valves face |
Abrasion Erosion Bending Twisting Flexing Temperature extreme |
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What is the purpose of a valve |
Allow gas to flow in or out of the compressor cylinder |
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What 4 components do most compressor valves require |
Sealing element that moves open and closed Valve seat for the sealing element to seal to Valve guard to act as a backstop and limit travel of sealing element Assembly elements to hold it all together |
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What are some common types of compressor valves |
Concentric rings and plate Dampened disk Poppet Feather Channel |
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valve uses two or more dampening disks |
dampened disk vales |
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what valve is suitable for high speed applications |
dampened disk valve |
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what valve is best suited for environments with condensate or other liquids |
poppet valve |
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what kind of valve uses a metal strip and requires no springs |
feather valve |
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what valve offers a good combination of effective gas cushioning flow and replacement of worn parts |
channel valves |
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what direction does a discharge valve open |
towards the nut |
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what direction should the nut be facing on valves with nuts |
outside of the cylinder |
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what direction does an intake valve upen |
away from the nut |
