Chapter 7 - Compressed Air Systems Flashcards
1
Q
How are air compressor plants classified?
A
Low-pressure, medium-pressure, and high-pressure.
2
Q
How are low-pressure system pressures reduced?
A
At reducing stations.
3
Q
Laboratories, shops, laundries and dry-cleaning plants, hospitals, ordinary service, and soot blowing for boilers are typically supported by which kind of pressure system?
A
Low-pressure systems.
4
Q
What are some characteristics of medium pressure systems?
A
They have individual compressors located near the loads and are typically not extensive.
5
Q
What are some main uses for medium pressure systems?
A
Starting of diesel engines, soot blowing of boilers and high temperature water generators, and hydraulic lifts.
6
Q
How can you minimize hazards associated with increased pressures in high-pressure systems?
A
By using separate compressors for each required pressure.
7
Q
How are small amounts of low pressure supplied to high-pressure systems?
A
Through pressure reducing stations.
8
Q
What is the risk associated with high-pressure systems?
A
Explosions caused by high-pressure air entering into pockets or dead ends that increase in temperature to the ignition point of the material.
9
Q
What are some classes of air entrapment?
A
Inert and chemical articulate, chemical gases, oil, and water.
10
Q
What should intake structures/openings be free of?
A
Shelves, pockets, or other surfaces that attract and accumulate particulate.
11
Q
How are properly designed intake structured?
A
With intakes that are large enough to produce a low-velocity airflow in order to limit the size of the particles that may be picked up by the intake suction.
12
Q
What is chemical particulate?
A
Particulate that contains active chemicals that can form acids or alkalines in the presence of water.
13
Q
How can chemical particulate cause damage?
A
By accelerating damage to compressor surfaces.
14
Q
How is particulate sized?
A
In microns or micrometers.
15
Q
What size particles should filters be able to remove?
A
1-3 microns in size.
16
Q
What size particles are visible to the naked eye?
A
Particles larger than 10 microns.
17
Q
What is compressed air measured as?
A
Pounds per square inch gauge (psig).
18
Q
How are gases and fumes damaging to the compressor?
A
They can corrosive to the internal surfaces or lubricants of the compressor.
19
Q
When make gases or fumes be prohibited?
A
By end of use processes such as medical gases or breathing air and for environmental or odor reasons.
20
Q
Where should you avoid placing intakes to avoid gas or fume air entrapment?
A
Near normal paths of engine exhausts.
21
Q
How can oils be damaging to compressors?
A
Although used for lubrication, the oil may not be compatible and can increase compressor load.
22
Q
How can water be damaging to compressors?
A
When water vapor mixes with chemicals it can corrode steel piping and damage internal components.
23
Q
How can you prevent or slow corrosion caused by water?
A
Galvanizing, applying protective coatings, or using plastic stainless steel piping for air intakes. Applying a weather good to exclude rainfall, snow, or spray.
24
Q
How is commercial compressed air graded?
A
By purity – A (most pure) thru J (least pure).
25
This is the guidelines for the grading of commercial compressed gas?
The Compressed Gas Association.
26
Where can you locate the quality requirements for commercial compressed air applications?
The Compressed Air Association publication, "Commodity Specification for Air, G-7. 1 (ANSI286. 1–1973)."
27
What must be eliminated from breathing air?
Carbon monoxide, carbon dioxide, hydrocarbons, order, and water.
28
What are some specifications for carbon monoxide monitoring?
It should be provided at the compressor intake and should sound an alarm or shut down the system when carbon monoxide is detected.
29
Where should compressor intakes be placed to avoid contaminating air with carbon dioxide?
Upwind or far from boiler stacks.
30
How can you limit concentrations of hydrocarbons are petroleum products in breathing air systems?
By keeping them free of oil rather than using auxiliary petroleum removal equipment.
31
What is the danger of hydrocarbons in the air system?
An explosion caused by heat from compression that breaks down oil.
32
How can you prevent or avoid increased water content and breathing air systems?
By keeping water content below saturation to prevent condensation at points that cannot be cleaned and using refrigerant or desiccant dryers to remove moisture from the breathing air system.
33
What are the specifications for medical air quality?
Quality must be the same or better than breathing air.
34
What are the specifications for air quality requirements for instrument and control air?
The moisture content and emphasis on cleanliness.
35
What are the established requirements for dew point exterior for instrument and control air set by the Instrument Society of America (ISA)?
18°F (-7.8°F) below minimum recorded ambient temperature.
36
How does the Instrument Society of America suggest that air intake be filtered for oil and water removal?
Through use of a refrigerant dryer with a dewpoint at least as low as 30°F.
37
How should compressed air for pneumatic tools be treated?
It should be filtered for particulate and water should be separated out.
38
What is the preferred method for oil ingestion into the air for tool lubrication?
Mist injection to ensure dispersion and maximum settlement.
39
What pressure may cause compression combustion in the presence of oil?
Pressures in excess of 400 psig.
40
What is the danger associated with air-quality in high-pressure air systems?
Explosions or fire that can be caused by the introduction of oil and hydrocarbons that accumulate during compression at pressures of 500 psig or higher.
41
How can you avoid explosions or fires in high pressure air systems through air quality?
By cleaning the air intake, limiting the introduction of lubrication oil, and removing oil after the compression process is complete.
42
What are some factors that determine the development of distribution systems?
Location and size of each service, time rate demand of larger services, and concurrence or demand factor of larger services.
43
What are some common types of air distribution systems?
Radial one-way system, loop system, and parallel system.
44
What is a radial, one-way system used for?
Isolated or individual service or where special requirements dictate a single path.
45
What is a loop system used for?
A closed route such as throughout a building to provide constant pressure to all services and selective isolation where needed.
46
What is a parallel system used for?
To provide tool service source to ensure at least one source will be available at all times.
47
How are compressed air distribution systems sized?
By calculating the friction loss to be expected from piping, fittings, and valves as well as various accessories you may install.
48
How should you compensate for contained pressure increases?
By increasing the pipe wall thickness and decreasing interior diameters.
49
What is the suggested limit for friction pressure loss?
Fiction pressure loss should not exceed 15 percent.
50
How do you determine total friction loss for a distribution system?
By adding the total length of the system piping to the the equivalent length of each fitting, valve, or device to produce an equivalent hydraulic length.
51
How can compressed airlines be installed in terms of level and pitch?
As level as practical with a slight pitch in the direction of airflow.
52
What are the suggested specifications for pitch placement?
3 inches per 100 feet of piping or 6 inches or greater per 100 feet with an increase in one pipe diameter when pipes must be pitched upward.
53
What are some considerations for the layout of piping systems to allow for adequate removal of dirt, water, oil, or other foreign material?
By avoiding pockets and providing low points with drip legs where necessary.
54
How can you prevent carryover of dirt, water, oil, and other foreign material into branch lines?
By making connections from the top of the distribution mains.
55
How should piping be placed in compressed air systems?
With sufficient flexibility to prevent excessive strain or distortion caused by thermal expansion or sudden changes in pressure. They should also support all changes in direction and load concentrations.
56
How should compressed air systems be tested?
At 150% of maximum working pressure using clean, dry air, or nitrogen held without loss for at least 4 hours.
57
How should prime mover maintenance be handled?
By establishing a lubrication schedule, maintaining normal oil levels in engines at all times, and using lubricants recommended by the manufacturer.
58
How are air compressor plants classified?
Low-pressure, medium-pressure, and high pressure.
59
How are low-pressure system pressures reduced?
At reducing stations.
60
What are some characteristics of medium pressure systems?
They have individual compressors located near the loads and are typically not extensive.
61
Starting of diesel engines, soot blowing of boilers and high temperature water generators, and hydraulic lifts are supported by what kind of pressure system?
Medium pressure systems.
62
How can you minimize hazards associated with increased pressures in high-pressure systems?
By using separate compressors for each required pressure.
63
How are small amounts of low pressure supplied to high-pressure systems?
Through pressure reducing stations.
64
What is the risk associated with high-pressure systems?
Explosions caused by high-pressure air entering into pockets or dead ends.
65
What is an explosion caused by combustible material in pocket or dead ends that reaches its ignition point in high-pressure air systems due to increased temperature called?
Auto ignition/diesel action.
66
Torpedo workshops, ammunition depots, wind tunnels, and testing laboratories are usually supported by what kind of pressure systems?
High-pressure systems.
67
What are some classes of air entrapment?
Inert and chemical articulate, chemical gases, oil, and water.
68
What should intake structures/openings be free of?
Shelves, pockets, or other surfaces that attract and accumulate particulate.
69
How are properly designed intake structured?
They must be large enough to produce a low-velocity airflow to limit the size of the particles that may be picked up by the intake suction.
70
What is chemical particulate?
Particulate that contains active chemicals that can form acids or alkalines in the presence of water.
71
How can chemical particulate cause damage?
By accelerating damage to compressor surfaces.
72
How is particulate sized?
In microns or micrometers.
73
What size particles should filters be able to remove?
1-3 microns in size.
74
What size particles are visible to the naked eye?
Particles larger than 10 microns.
75
What is compressed air measured as?
Pounds per square inch gauge (psig).
76
What determines the frequency of oil changes?
The severity of service, atmospheric dust, and dirt.
77
How is a medium pressure system classified?
126-399 psig
78
How is a high pressure system classified?
400-6000 psig.
79
What are the pressure ranger for laboratories?
5-50 psig.
80
What are the pressure ranges for shops?
60-125 psig.
81
What are the pressure ranges for laundries and dry cleaning plants?
70-100 psig.
82
What are the pressure ranges for hospitals?
20-100 psig.
83
What are the pressure ranges for ordinary services?
60-80 psig.
84
What are the pressure requirements for soot blowing for boilers?
80-125 psig.
85
What are the pressure ranges for torpedo workshops?
600-3000 psig.
86
What are the pressure ranges for ammunition depots.
100, 750, 1500, 2000, and 4500 psig.
87
What are the pressure ranges for wind tunnels?
Over 3000 psig.
88
What are the pressure ranges for testing laboratories?
Up to 6000 psig.
89
What are the established requirements for dew point interior for instrument and control air set by the Instrument Society of America (ISA)?
18°F (-7.8°C) below minimum interior temperature but not higher than 35°F (1.7°C)
90
What are the established requirements for particle size for instrument and control air set by the Instrument Society of America (ISA)?
3 microns maximum.
91
What are the established requirements for oil content for instrument and control air set by the Instrument Society of America (ISA)?
As close to zero as possible but not over 1 ppm.
92
What are the established requirements for contaminants for instrument and control air set by the Instrument Society of America (ISA)?
No corrosives or hazardous gases.
93
How should air compressor maintenance be handled?
Establish a lubrication schedule, assign and and schedule responsibilities for maintenance personnel to follow, visually inspect for dust/dirt/leaks.
94
What should be included on the maintenance schedule for air compressors?
Bearings, packing a, seals, and clearances between moving parts.
95
How can air compressors be maintained for clearances?
They may be adjusted or overhauled when clearances are exceeded.
96
How often should air filters be checked and cleaned?
At least once a month.
97
How often should silencers be checked for corrosion, paint, and gasket damage?
Twice a year.
98
What must intercoolers and after coolers be inspected for?
Scale buildup in hub leaks.
99
How should distribution system maintenance be handled?
By checking valve operation and hose connectors, draining condensation, protecting piping from damage, and repairing leaks.
100
Where can you find procedures for preventative maintenance inspections for compressed air plants?
NAVFAC MO 209, Steam, Hot Water, and Compressed Air. NAVFAC P-171, Preventitve/Recurring Maintenance Handbook.
101
How is a low system pressure classified?
0-125 psig
102
What are two main types of compressors?
Positive displacement and dynamic.
103
What type of compressor is a reciprocating air compressor?
Positive displacement compressor.
104
What type of compressor is a rotary air compressor?
Positive displacement compressor.
105
What type of compressor is a helical screw compressor?
Positive displacement compressor.
106
What type of compressor is a dynamic centrifugal compressor?
Dynamic compressor.
107
What is the most commonly used stationary air compressor?
Reciprocating air compressor.
108
How many compressing elements are in a single stage unit?
One.
109
How does a single stage unit reciprocating air compressor work?
It compresses air from the initial intake to final discharge in one step.
110
How many compressing elements does a multistage unit have?
More than one.
111
How does a multistage unit reciprocating air compressor work?
It compresses air to an intermediate pressure in the first stage and takes additional stages to compress to the final discharge pressure.
112
What are the three phases in the compression cycle?
Intake, compression, and discharge.
113
The downward movement of the piston that creates a vacuum which opens the intake valve occurs during which phase of the compression cycle?
The intake phase.
114
The closing of the intake valve and increase in pressure of air trapped in the cylinder occurs during which phase of the compression cycle?
The compression phase.
115
The opening of the discharge valve by the pressure compressed air in the cylinder causing a release of air occurs during which phase of the conversion cycle?
The discharge phase.
116
How are compressors classified?
Low pressure, medium pressure, and high pressure.
117
What is the discharge pressure of a low pressure compressor?
150 psi or less.
118
What is the discharge pressure of a medium pressure compressor?
151 psi to 1000 psi.
119
What is the discharge pressure of a high pressure compressor?
Above 1000 PSI.
120
How are most low pressure air compressors configured?
Two stage with a vertical (v type) or vertical W (w type) cylinder arrangement.
121
What type of low pressure air compressor has one cylinder for the first stage of compression and one cylinder for the second stage of compression?
Two-stage V type.
122
What type of low pressure air compressor has two cylinders for the first stage of compression and one cylinder for the second stage?
Two-stage W type.
123
How are most medium pressure air compressors configured?
Two stage, vertical, duplex, or single acting.
124
What type of pistons do most medium pressure compressors have?
Differential pistons.
125
What do you differential pistons do?
Provide more than one stage of compression per piston.
126
What are two types of rotary air compressors?
Rotary sliding vane and twin lobe unit (blower).
127
Which type of rotary air compressor has a rotor with a blade that slides in and out of slots that force the blade outward to form compartments for air compression?
Rotary sliding vane.
128
Which type of rotary air compressor uses two impellers located parallel to one another that rotate in opposite directions to trap air?
Twin lobe units.
129
Which type of compressor uses one locked and one grooved rotating screw to drive air intake?
Helical screw compressors.
130
Where are helical screw compressors best used?
In near constant load conditions at low pressure, oil free application.
131
What kind of compressors utilize high-speed rotating machines to rotate impellers and blades to compressed air?
Dynamic centrifugal compressor.
132
What is the lower limit of stable operation in a centrifugal compressor called?
A surge point.
133
When are centrifugal compressors used?
Continuous industrial air services where load is constant, for oil free air, and breathing air.
134
What is the minimum auxiliary equipment required for a compressed air system?
Air intakes, intake filters, silencers, intercoolers, after coolers, or discharge system, separators, dryer, and receivers.
135
Where should air intakes be placed?
High enough to eliminate particulate intake, avoid carbon monoxide discharge, and eliminate the intake of flammable fumes.
136
How should air intakes be placed through roofing that is surrounded by parapets?
8 to 10 feet above the roof.
137
How can you help eliminate intake piping resonance?
By using intake dampeners or surge chambers.
138
What are the suggested limits for intake pipe velocities?
1000 FPM in open areas, 350 FPM across filters.
139
What is the purpose of an intake filter?
To prevent dust from entering the cylinders and cause excessive wear.
140
What are the two most common types of air filters?
Viscous impingement and oil bath.
141
When are oil bath filters recommended?
Where dust concentrations are present in the atmosphere.
142
How do you oil bath filters remove particles?
There an oil seal which then passes through a wire mesh filter element.
143
How do viscous impingement filters remove particles?
There and oil coated mesh filter element
144
What is the function of a silencer?
To eliminate compressor suction noise.
145
What is the purpose of an intercooler?
To reduce the temperature of compression from each stage.
146
What is the purpose of intercooling?
To increase compressor efficiency, prevent excessive temperatures, and condense moisture.
147
What are some of the common intercooler types?
Shell and tube, air to water heat exchangers, and air cooled radiator type heat exchangers.
148
What is the purpose of an after cooler?
To lower discharge temperature and condense moisture for removal.
149
What do positive displacement compressors required to protect the piping upstream of the shut off valve?
A relief valve.
150
How should relief valves be sized?
For 125% of the maximum unit flow capacity.
151
What is the function of a separator?
To separate excess freewater from discharge air and gas.
152
How do centrifugal separators work?
By throwing moisture particles in a swirling motion to the wall to be drained.
153
How do you baffle type separators work?
By using sudden changes in direction to throw moisture particles to the wall for draining.
154
What is the function of a dryer?
To ensure removal of all moisture.
155
What are the basic types of dryers?
Absorption and condensation.
156
What are the two types of absorption dryers?
A two tower unit with absorbent material and a single tank with desiccant.
157
How are absorbent materials in a two tower absorption dryer reactivated?
By electrical/stream heaters or dried processed air.
158
How do condensation dryers is remove moisture?
By using a refrigeration unit of cold water to condense air.
159
What is the purpose of an air receiver tank?
To smooth airflow from compression to discharge and collect excessive moisture.
160
Relief valves, pressure gauges, drain valves, service valves, and inspection openings are components of a?
Receiver.
161
What is the flashpoint of typical compressor cylinder oils?
350°F minimum.
162
What is the viscosity of typical compressor cylinder oils?
Viscosity at 210°F, 45 minimum to 90 maximum.
163
What is the pour point of typical compressor cylinder oils?
+35°F max.
164
What is the neutralization number of typical compressor cylinder oils?
0.10 max.
165
What is the Conradson carbon residue maximum of typical cylinder oils?
2.0%
166
What is a special consideration for lubricant during cold weather?
Including a lubrication heater for adequate viscosity.
167
How can discharge pulsations damage compressors?
By causing support and piping damage.
168
How do you pulsation dampeners muffle noise and pulsations?
By using acoustical chambers with the dampener.
169
How much do manufactures typically provide dampers to function at?
To a discharge pulsation peak of +/- 2% of line pressure.
170
When should dampeners be used?
When reciprocating and centrifugal compressors serve the same compressed air main.
171
How can surge chambers be used to decrease noise and discharge pulsation amplification?
By changing the equivalent length of the piping and increasing the pulse absorbing volume.
172
How must piping be supported to accommodate discharge pulsations?
Top, bottom, and laterally.
173
How should larger piping be supported to accommodate discharge pulsations?
By using spring-loaded two way lateral supports in addition to top and bottom supports.
174
How can prime movers for compressors be driven?
Electrically, gasoline, and diesel.
175
What type of electric motors can be used for compressors?
Induction, synchronous wound motors, and direct current motors.
176
What types of drives may be used to connect motors and compressors?
Belt, direct connection, or speed reduction gears.
177
When are induction motors used?
For single acting reciprocating compressors up to 300 hp at 1800 RPM.
178
What should be considered when sizing a motor?
Allowance for belt or drive losses of power.
179
What kind of motors are best belted to compressors?
Normal starting torque, low starting current motors.
180
How should belts be considered for motors?
Based on a continuous operation rating of at least 125%, 150% preferred.
181
How can lengthened acceleration times be avoided in compressors?
By arranging for compressors to be unloaded during start up.
182
What does the use of a speed reduction gear to connect the motor to the compressor enable?
The use of higher speeds with a less costly motor.
183
How should speed reduction gear connections be configured to prevent damage?
With enough elasticity and dampening between couplings to allow for torque and pulsations.
184
What is the purpose of compressor control systems?
To regulate the output of the compressor as it meets the demand for compressed air.
185
What type of controller activates the prime mover over a predetermined pressure range?
Simple Bourdon type controller.
186
What type of controller increases or decreases compressor capacity while allowing the prime mover speed to remain constant?
Constant speed type controller.
187
What type of controller permits constant speed when demands are continuous and an automatic stop or start when loads are light?
Dual control type.
188
What do you control systems generally include?
Unloading devices.
189
What type of unloading device holds the inlet valve open mechanically during suction and compression strokes to prevent compression?
Inlet valve type.
190
The use of a solenoid unloader valve enables what kind of control?
Sequenced capacity control.
191
How much of the compressor capacity will unload once the receiver pressure reaches the high limit of each switch in an inlet valve type unloader?
25%
192
How much of the compressor capacity will load once the receiver pressure reaches the low limit of each switch in an inlet valve type unloader?
25%
193
Other than inlet valve unloaders, how else may compressors be unloaded?
Clearance pockets.
194
What is normal clearance?
The volume at the end of the piston and under the valves at the end of compassion.
195
How do you clearance pockets unload compressors?
By opening and closing at the end of the cylinder using pilot valves as directed by the receiver pressure.
196
How much air can each clearance pocket hold?
One quarter of air compressed by the cylinder in one stroke.
