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UT advanced > Chapter 7 - Compressed Air Systems > Flashcards

Chapter 7 - Compressed Air Systems Flashcards

1
Q

How are air compressor plants classified?

A

Low-pressure, medium-pressure, and high-pressure.

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2
Q

How are low-pressure system pressures reduced?

A

At reducing stations.

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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.

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4
Q

What are some characteristics of medium pressure systems?

A

They have individual compressors located near the loads and are typically not extensive.

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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.

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6
Q

How can you minimize hazards associated with increased pressures in high-pressure systems?

A

By using separate compressors for each required pressure.

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7
Q

How are small amounts of low pressure supplied to high-pressure systems?

A

Through pressure reducing stations.

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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.

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9
Q

What are some classes of air entrapment?

A

Inert and chemical articulate, chemical gases, oil, and water.

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10
Q

What should intake structures/openings be free of?

A

Shelves, pockets, or other surfaces that attract and accumulate particulate.

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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.

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12
Q

What is chemical particulate?

A

Particulate that contains active chemicals that can form acids or alkalines in the presence of water.

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13
Q

How can chemical particulate cause damage?

A

By accelerating damage to compressor surfaces.

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14
Q

How is particulate sized?

A

In microns or micrometers.

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15
Q

What size particles should filters be able to remove?

A

1-3 microns in size.

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16
Q

What size particles are visible to the naked eye?

A

Particles larger than 10 microns.

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17
Q

What is compressed air measured as?

A

Pounds per square inch gauge (psig).

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18
Q

How are gases and fumes damaging to the compressor?

A

They can corrosive to the internal surfaces or lubricants of the compressor.

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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.

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20
Q

Where should you avoid placing intakes to avoid gas or fume air entrapment?

A

Near normal paths of engine exhausts.

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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.

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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.

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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.

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24
Q

How is commercial compressed air graded?

A

By purity – A (most pure) thru J (least pure).

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25
Q

This is the guidelines for the grading of commercial compressed gas?

A

The Compressed Gas Association.

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26
Q

Where can you locate the quality requirements for commercial compressed air applications?

A

The Compressed Air Association publication, “Commodity Specification for Air, G-7. 1 (ANSI286. 1–1973).”

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27
Q

What must be eliminated from breathing air?

A

Carbon monoxide, carbon dioxide, hydrocarbons, order, and water.

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28
Q

What are some specifications for carbon monoxide monitoring?

A

It should be provided at the compressor intake and should sound an alarm or shut down the system when carbon monoxide is detected.

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29
Q

Where should compressor intakes be placed to avoid contaminating air with carbon dioxide?

A

Upwind or far from boiler stacks.

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30
Q

How can you limit concentrations of hydrocarbons are petroleum products in breathing air systems?

A

By keeping them free of oil rather than using auxiliary petroleum removal equipment.

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31
Q

What is the danger of hydrocarbons in the air system?

A

An explosion caused by heat from compression that breaks down oil.

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32
Q

How can you prevent or avoid increased water content and breathing air systems?

A

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.

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33
Q

What are the specifications for medical air quality?

A

Quality must be the same or better than breathing air.

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34
Q

What are the specifications for air quality requirements for instrument and control air?

A

The moisture content and emphasis on cleanliness.

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35
Q

What are the established requirements for dew point exterior for instrument and control air set by the Instrument Society of America (ISA)?

A

18°F (-7.8°F) below minimum recorded ambient temperature.

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36
Q

How does the Instrument Society of America suggest that air intake be filtered for oil and water removal?

A

Through use of a refrigerant dryer with a dewpoint at least as low as 30°F.

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37
Q

How should compressed air for pneumatic tools be treated?

A

It should be filtered for particulate and water should be separated out.

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38
Q

What is the preferred method for oil ingestion into the air for tool lubrication?

A

Mist injection to ensure dispersion and maximum settlement.

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39
Q

What pressure may cause compression combustion in the presence of oil?

A

Pressures in excess of 400 psig.

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40
Q

What is the danger associated with air-quality in high-pressure air systems?

A

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.

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41
Q

How can you avoid explosions or fires in high pressure air systems through air quality?

A

By cleaning the air intake, limiting the introduction of lubrication oil, and removing oil after the compression process is complete.

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42
Q

What are some factors that determine the development of distribution systems?

A

Location and size of each service, time rate demand of larger services, and concurrence or demand factor of larger services.

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43
Q

What are some common types of air distribution systems?

A

Radial one-way system, loop system, and parallel system.

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44
Q

What is a radial, one-way system used for?

A

Isolated or individual service or where special requirements dictate a single path.

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45
Q

What is a loop system used for?

A

A closed route such as throughout a building to provide constant pressure to all services and selective isolation where needed.

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46
Q

What is a parallel system used for?

A

To provide tool service source to ensure at least one source will be available at all times.

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47
Q

How are compressed air distribution systems sized?

A

By calculating the friction loss to be expected from piping, fittings, and valves as well as various accessories you may install.

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48
Q

How should you compensate for contained pressure increases?

A

By increasing the pipe wall thickness and decreasing interior diameters.

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49
Q

What is the suggested limit for friction pressure loss?

A

Fiction pressure loss should not exceed 15 percent.

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50
Q

How do you determine total friction loss for a distribution system?

A

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.

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51
Q

How can compressed airlines be installed in terms of level and pitch?

A

As level as practical with a slight pitch in the direction of airflow.

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52
Q

What are the suggested specifications for pitch placement?

A

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.

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53
Q

What are some considerations for the layout of piping systems to allow for adequate removal of dirt, water, oil, or other foreign material?

A

By avoiding pockets and providing low points with drip legs where necessary.

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54
Q

How can you prevent carryover of dirt, water, oil, and other foreign material into branch lines?

A

By making connections from the top of the distribution mains.

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55
Q

How should piping be placed in compressed air systems?

A

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.

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56
Q

How should compressed air systems be tested?

A

At 150% of maximum working pressure using clean, dry air, or nitrogen held without loss for at least 4 hours.

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57
Q

How should prime mover maintenance be handled?

A

By establishing a lubrication schedule, maintaining normal oil levels in engines at all times, and using lubricants recommended by the manufacturer.

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58
Q

How are air compressor plants classified?

A

Low-pressure, medium-pressure, and high pressure.

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59
Q

How are low-pressure system pressures reduced?

A

At reducing stations.

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60
Q

What are some characteristics of medium pressure systems?

A

They have individual compressors located near the loads and are typically not extensive.

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61
Q

Starting of diesel engines, soot blowing of boilers and high temperature water generators, and hydraulic lifts are supported by what kind of pressure system?

A

Medium pressure systems.

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62
Q

How can you minimize hazards associated with increased pressures in high-pressure systems?

A

By using separate compressors for each required pressure.

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63
Q

How are small amounts of low pressure supplied to high-pressure systems?

A

Through pressure reducing stations.

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64
Q

What is the risk associated with high-pressure systems?

A

Explosions caused by high-pressure air entering into pockets or dead ends.

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65
Q

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?

A

Auto ignition/diesel action.

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66
Q

Torpedo workshops, ammunition depots, wind tunnels, and testing laboratories are usually supported by what kind of pressure systems?

A

High-pressure systems.

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67
Q

What are some classes of air entrapment?

A

Inert and chemical articulate, chemical gases, oil, and water.

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68
Q

What should intake structures/openings be free of?

A

Shelves, pockets, or other surfaces that attract and accumulate particulate.

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69
Q

How are properly designed intake structured?

A

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.

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70
Q

What is chemical particulate?

A

Particulate that contains active chemicals that can form acids or alkalines in the presence of water.

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71
Q

How can chemical particulate cause damage?

A

By accelerating damage to compressor surfaces.

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72
Q

How is particulate sized?

A

In microns or micrometers.

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73
Q

What size particles should filters be able to remove?

A

1-3 microns in size.

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74
Q

What size particles are visible to the naked eye?

A

Particles larger than 10 microns.

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75
Q

What is compressed air measured as?

A

Pounds per square inch gauge (psig).

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76
Q

What determines the frequency of oil changes?

A

The severity of service, atmospheric dust, and dirt.

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77
Q

How is a medium pressure system classified?

A

126-399 psig

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78
Q

How is a high pressure system classified?

A

400-6000 psig.

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79
Q

What are the pressure ranger for laboratories?

A

5-50 psig.

80
Q

What are the pressure ranges for shops?

A

60-125 psig.

81
Q

What are the pressure ranges for laundries and dry cleaning plants?

A

70-100 psig.

82
Q

What are the pressure ranges for hospitals?

A

20-100 psig.

83
Q

What are the pressure ranges for ordinary services?

A

60-80 psig.

84
Q

What are the pressure requirements for soot blowing for boilers?

A

80-125 psig.

85
Q

What are the pressure ranges for torpedo workshops?

A

600-3000 psig.

86
Q

What are the pressure ranges for ammunition depots.

A

100, 750, 1500, 2000, and 4500 psig.

87
Q

What are the pressure ranges for wind tunnels?

A

Over 3000 psig.

88
Q

What are the pressure ranges for testing laboratories?

A

Up to 6000 psig.

89
Q

What are the established requirements for dew point interior for instrument and control air set by the Instrument Society of America (ISA)?

A

18°F (-7.8°C) below minimum interior temperature but not higher than 35°F (1.7°C)

90
Q

What are the established requirements for particle size for instrument and control air set by the Instrument Society of America (ISA)?

A

3 microns maximum.

91
Q

What are the established requirements for oil content for instrument and control air set by the Instrument Society of America (ISA)?

A

As close to zero as possible but not over 1 ppm.

92
Q

What are the established requirements for contaminants for instrument and control air set by the Instrument Society of America (ISA)?

A

No corrosives or hazardous gases.

93
Q

How should air compressor maintenance be handled?

A

Establish a lubrication schedule, assign and and schedule responsibilities for maintenance personnel to follow, visually inspect for dust/dirt/leaks.

94
Q

What should be included on the maintenance schedule for air compressors?

A

Bearings, packing a, seals, and clearances between moving parts.

95
Q

How can air compressors be maintained for clearances?

A

They may be adjusted or overhauled when clearances are exceeded.

96
Q

How often should air filters be checked and cleaned?

A

At least once a month.

97
Q

How often should silencers be checked for corrosion, paint, and gasket damage?

A

Twice a year.

98
Q

What must intercoolers and after coolers be inspected for?

A

Scale buildup in hub leaks.

99
Q

How should distribution system maintenance be handled?

A

By checking valve operation and hose connectors, draining condensation, protecting piping from damage, and repairing leaks.

100
Q

Where can you find procedures for preventative maintenance inspections for compressed air plants?

A

NAVFAC MO 209, Steam, Hot Water, and Compressed Air. NAVFAC P-171, Preventitve/Recurring Maintenance Handbook.

101
Q

How is a low system pressure classified?

A

0-125 psig

102
Q

What are two main types of compressors?

A

Positive displacement and dynamic.

103
Q

What type of compressor is a reciprocating air compressor?

A

Positive displacement compressor.

104
Q

What type of compressor is a rotary air compressor?

A

Positive displacement compressor.

105
Q

What type of compressor is a helical screw compressor?

A

Positive displacement compressor.

106
Q

What type of compressor is a dynamic centrifugal compressor?

A

Dynamic compressor.

107
Q

What is the most commonly used stationary air compressor?

A

Reciprocating air compressor.

108
Q

How many compressing elements are in a single stage unit?

A

One.

109
Q

How does a single stage unit reciprocating air compressor work?

A

It compresses air from the initial intake to final discharge in one step.

110
Q

How many compressing elements does a multistage unit have?

A

More than one.

111
Q

How does a multistage unit reciprocating air compressor work?

A

It compresses air to an intermediate pressure in the first stage and takes additional stages to compress to the final discharge pressure.

112
Q

What are the three phases in the compression cycle?

A

Intake, compression, and discharge.

113
Q

The downward movement of the piston that creates a vacuum which opens the intake valve occurs during which phase of the compression cycle?

A

The intake phase.

114
Q

The closing of the intake valve and increase in pressure of air trapped in the cylinder occurs during which phase of the compression cycle?

A

The compression phase.

115
Q

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?

A

The discharge phase.

116
Q

How are compressors classified?

A

Low pressure, medium pressure, and high pressure.

117
Q

What is the discharge pressure of a low pressure compressor?

A

150 psi or less.

118
Q

What is the discharge pressure of a medium pressure compressor?

A

151 psi to 1000 psi.

119
Q

What is the discharge pressure of a high pressure compressor?

A

Above 1000 PSI.

120
Q

How are most low pressure air compressors configured?

A

Two stage with a vertical (v type) or vertical W (w type) cylinder arrangement.

121
Q

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?

A

Two-stage V type.

122
Q

What type of low pressure air compressor has two cylinders for the first stage of compression and one cylinder for the second stage?

A

Two-stage W type.

123
Q

How are most medium pressure air compressors configured?

A

Two stage, vertical, duplex, or single acting.

124
Q

What type of pistons do most medium pressure compressors have?

A

Differential pistons.

125
Q

What do you differential pistons do?

A

Provide more than one stage of compression per piston.

126
Q

What are two types of rotary air compressors?

A

Rotary sliding vane and twin lobe unit (blower).

127
Q

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?

A

Rotary sliding vane.

128
Q

Which type of rotary air compressor uses two impellers located parallel to one another that rotate in opposite directions to trap air?

A

Twin lobe units.

129
Q

Which type of compressor uses one locked and one grooved rotating screw to drive air intake?

A

Helical screw compressors.

130
Q

Where are helical screw compressors best used?

A

In near constant load conditions at low pressure, oil free application.

131
Q

What kind of compressors utilize high-speed rotating machines to rotate impellers and blades to compressed air?

A

Dynamic centrifugal compressor.

132
Q

What is the lower limit of stable operation in a centrifugal compressor called?

A

A surge point.

133
Q

When are centrifugal compressors used?

A

Continuous industrial air services where load is constant, for oil free air, and breathing air.

134
Q

What is the minimum auxiliary equipment required for a compressed air system?

A

Air intakes, intake filters, silencers, intercoolers, after coolers, or discharge system, separators, dryer, and receivers.

135
Q

Where should air intakes be placed?

A

High enough to eliminate particulate intake, avoid carbon monoxide discharge, and eliminate the intake of flammable fumes.

136
Q

How should air intakes be placed through roofing that is surrounded by parapets?

A

8 to 10 feet above the roof.

137
Q

How can you help eliminate intake piping resonance?

A

By using intake dampeners or surge chambers.

138
Q

What are the suggested limits for intake pipe velocities?

A

1000 FPM in open areas, 350 FPM across filters.

139
Q

What is the purpose of an intake filter?

A

To prevent dust from entering the cylinders and cause excessive wear.

140
Q

What are the two most common types of air filters?

A

Viscous impingement and oil bath.

141
Q

When are oil bath filters recommended?

A

Where dust concentrations are present in the atmosphere.

142
Q

How do you oil bath filters remove particles?

A

There an oil seal which then passes through a wire mesh filter element.

143
Q

How do viscous impingement filters remove particles?

A

There and oil coated mesh filter element

144
Q

What is the function of a silencer?

A

To eliminate compressor suction noise.

145
Q

What is the purpose of an intercooler?

A

To reduce the temperature of compression from each stage.

146
Q

What is the purpose of intercooling?

A

To increase compressor efficiency, prevent excessive temperatures, and condense moisture.

147
Q

What are some of the common intercooler types?

A

Shell and tube, air to water heat exchangers, and air cooled radiator type heat exchangers.

148
Q

What is the purpose of an after cooler?

A

To lower discharge temperature and condense moisture for removal.

149
Q

What do positive displacement compressors required to protect the piping upstream of the shut off valve?

A

A relief valve.

150
Q

How should relief valves be sized?

A

For 125% of the maximum unit flow capacity.

151
Q

What is the function of a separator?

A

To separate excess freewater from discharge air and gas.

152
Q

How do centrifugal separators work?

A

By throwing moisture particles in a swirling motion to the wall to be drained.

153
Q

How do you baffle type separators work?

A

By using sudden changes in direction to throw moisture particles to the wall for draining.

154
Q

What is the function of a dryer?

A

To ensure removal of all moisture.

155
Q

What are the basic types of dryers?

A

Absorption and condensation.

156
Q

What are the two types of absorption dryers?

A

A two tower unit with absorbent material and a single tank with desiccant.

157
Q

How are absorbent materials in a two tower absorption dryer reactivated?

A

By electrical/stream heaters or dried processed air.

158
Q

How do condensation dryers is remove moisture?

A

By using a refrigeration unit of cold water to condense air.

159
Q

What is the purpose of an air receiver tank?

A

To smooth airflow from compression to discharge and collect excessive moisture.

160
Q

Relief valves, pressure gauges, drain valves, service valves, and inspection openings are components of a?

A

Receiver.

161
Q

What is the flashpoint of typical compressor cylinder oils?

A

350°F minimum.

162
Q

What is the viscosity of typical compressor cylinder oils?

A

Viscosity at 210°F, 45 minimum to 90 maximum.

163
Q

What is the pour point of typical compressor cylinder oils?

A

+35°F max.

164
Q

What is the neutralization number of typical compressor cylinder oils?

A

0.10 max.

165
Q

What is the Conradson carbon residue maximum of typical cylinder oils?

A

2.0%

166
Q

What is a special consideration for lubricant during cold weather?

A

Including a lubrication heater for adequate viscosity.

167
Q

How can discharge pulsations damage compressors?

A

By causing support and piping damage.

168
Q

How do you pulsation dampeners muffle noise and pulsations?

A

By using acoustical chambers with the dampener.

169
Q

How much do manufactures typically provide dampers to function at?

A

To a discharge pulsation peak of +/- 2% of line pressure.

170
Q

When should dampeners be used?

A

When reciprocating and centrifugal compressors serve the same compressed air main.

171
Q

How can surge chambers be used to decrease noise and discharge pulsation amplification?

A

By changing the equivalent length of the piping and increasing the pulse absorbing volume.

172
Q

How must piping be supported to accommodate discharge pulsations?

A

Top, bottom, and laterally.

173
Q

How should larger piping be supported to accommodate discharge pulsations?

A

By using spring-loaded two way lateral supports in addition to top and bottom supports.

174
Q

How can prime movers for compressors be driven?

A

Electrically, gasoline, and diesel.

175
Q

What type of electric motors can be used for compressors?

A

Induction, synchronous wound motors, and direct current motors.

176
Q

What types of drives may be used to connect motors and compressors?

A

Belt, direct connection, or speed reduction gears.

177
Q

When are induction motors used?

A

For single acting reciprocating compressors up to 300 hp at 1800 RPM.

178
Q

What should be considered when sizing a motor?

A

Allowance for belt or drive losses of power.

179
Q

What kind of motors are best belted to compressors?

A

Normal starting torque, low starting current motors.

180
Q

How should belts be considered for motors?

A

Based on a continuous operation rating of at least 125%, 150% preferred.

181
Q

How can lengthened acceleration times be avoided in compressors?

A

By arranging for compressors to be unloaded during start up.

182
Q

What does the use of a speed reduction gear to connect the motor to the compressor enable?

A

The use of higher speeds with a less costly motor.

183
Q

How should speed reduction gear connections be configured to prevent damage?

A

With enough elasticity and dampening between couplings to allow for torque and pulsations.

184
Q

What is the purpose of compressor control systems?

A

To regulate the output of the compressor as it meets the demand for compressed air.

185
Q

What type of controller activates the prime mover over a predetermined pressure range?

A

Simple Bourdon type controller.

186
Q

What type of controller increases or decreases compressor capacity while allowing the prime mover speed to remain constant?

A

Constant speed type controller.

187
Q

What type of controller permits constant speed when demands are continuous and an automatic stop or start when loads are light?

A

Dual control type.

188
Q

What do you control systems generally include?

A

Unloading devices.

189
Q

What type of unloading device holds the inlet valve open mechanically during suction and compression strokes to prevent compression?

A

Inlet valve type.

190
Q

The use of a solenoid unloader valve enables what kind of control?

A

Sequenced capacity control.

191
Q

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?

A

25%

192
Q

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?

A

25%

193
Q

Other than inlet valve unloaders, how else may compressors be unloaded?

A

Clearance pockets.

194
Q

What is normal clearance?

A

The volume at the end of the piston and under the valves at the end of compassion.

195
Q

How do you clearance pockets unload compressors?

A

By opening and closing at the end of the cylinder using pilot valves as directed by the receiver pressure.

196
Q

How much air can each clearance pocket hold?

A

One quarter of air compressed by the cylinder in one stroke.

UT advanced (8 decks)

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