1
Q
What are some uses of compressed air in buildings?(10)
A
- Operating heating, air conditioning, and refrigeration control systems
- Operating power-actuated devices
- Starting emergency equipment
- Atomizing fuel oil in boiler combustion equipment
- Creating a water spray in air humidification equipment
- Mixing or agitating in water treatment processes
- Operating tools
- Spray painting
- Operating fire protection equipment
- Blast cleaning or sandblasting surfaces
Compressed air is essential for operating much of the equipment found in large industrial, commercial, and residential buildings.
2
Q
What are the advantages of using compressed air to drive tools and machinery?(7)
A
- Overloading cannot damage air compressors
- Air driven hand tools are lighter in weight
- Air driven hand tools do not become hot after extensive use
- Air driven hand tools do not create a shock hazard
- Compressed air machinery may be used safely in explosive atmospheres
- Transmission losses are less with compressed air than with steam
- Air piping will not become hot enough to create a burn hazard
These advantages make compressed air a preferred choice in various applications.
3
Q
What are the disadvantages associated with air compressors?(2)
A
- Compressed air tools are usually more expensive than electrically driven tools
- Air transmission piping is more expensive and difficult to install than electrical wiring
Engineers will be expected to discuss these disadvantages.
4
Q
What are the two categories of air compressors?
A
- Positive displacement compressors
- Dynamic compressors
Their configurations and operation are similar to pumps.
5
Q
Describe the operation of a positive displacement compressor.
A
Draws in a charge of free air, traps it, reduces its volume, and discharges it
This type may be a reciprocating or rotary type.
6
Q
What is the function of a dynamic compressor?
A
Accelerates air using impellers or blades, converting kinetic energy into potential energy
Examples include centrifugal and axial flow compressors.
7
Q
What is a reciprocating compressor?
A
Air is compressed by a piston moving back and forth within a cylinder
This type is used in various applications, including power plant service and mining installations.
8
Q
What is the difference between single-acting and double-acting compressors?
A
- Single-acting: Compression and discharge at one end of the cylinder
- Double-acting: Compression and discharge at both ends of the cylinder
This affects the number of compression strokes per revolution of the crankshaft.
9
Q
What components are required for a double-acting compressor?(4)
A
- Cylinder closed at both ends
- Piston rod
- Crosshead
- Connecting rod
These components transmit energy from the crankshaft to the piston.
10
Q
What happens when the piston moves to the left in a double-acting compressor?(3)
A
- A partial vacuum is formed
- Air is drawn in through the right-hand intake valve
- Air is compressed and forced out through the left-hand discharge valve
This process is part of the air compression cycle in a double-acting compressor.
11
Q
What occurs when the piston moves to the right in a double-acting compressor?(3)
A
- Air is compressed to the right of the piston
- Air is forced through the right-hand discharge valve
- Air is drawn into the cylinder through the left-hand intake valve
The movement of the piston alternates the intake and discharge of air.
12
Q
In a double-acting compressor, when the left intake valve is open, which other valve is also open?
A
Right discharge valve
This configuration allows for simultaneous intake and discharge during the compression cycle.
13
Q
What is the primary difference between single-stage and two-stage compressors?(2)
A
- Single-stage compressors compress air in one step
- Two-stage compressors compress air in two steps with an intercooler
The choice between single-stage and two-stage depends on the required operating pressure.
14
Q
What is the function of a finned intercooler in a two-stage compressor?
A
To reduce the air temperature between compression stages
This helps improve efficiency and performance of the compressor.
15
Q
What are the common designs of rotary compressors?(3)
A
- Sliding vane type
- Rotary lobe type
- Rotary screw type
These designs are classified as positive displacement types.
16
Q
Describe the operation of a sliding vane compressor.(3)
A
- Consists of a cylindrical rotor with sliding vanes
- Rotor is eccentric to the casing
- Air pockets are trapped and compressed as the rotor turns
The design allows for efficient compression of air through centrifugal force.
17
Q
In a two-stage sliding vane compressor, what happens to the air after it is compressed in the low-pressure stage?
A
It flows through an intercooler to the high-pressure compressor
This process enhances the efficiency of air compression.
18
Q
What is the role of the crosshead, connecting, and piston rods in a compressor?
A
To facilitate the movement and operation of the piston
These components are essential for the mechanical function of the compressor.
19
Q
What is the maximum discharge pressure that compressors may reach?
A
1000 kPa (145 psi)
This pressure is typical for various types of compressors.
20
Q
What type of motor is most commonly used to drive compressors?
A
Directly connected induction motor
Internal combustion engines can also be used with speed-reducing or speed-increasing gears.
21
Q
What is the purpose of a belt-driven lubricator in compressors?
A
Provides lubrication under pressure to bearings and cylinders
This is essential for the proper functioning of the compressor.
22
Q
What is a key advantage of the sliding vane compressor?
A
Does not require inlet or discharge valves
This feature is common to all rotating compressors.
23
Q
Describe the operation of a rotary lobe compressor.
A
Two figure-eight shaped impellers revolving in opposite directions
The impellers maintain their positions using timing gears and do not contact each other, making it oil-free.
24
Q
What is the typical speed range for a lobe compressor?
A
Up to about 1750 r/min
It may be directly driven by an induction motor or internal combustion engine.
25
What is the maximum discharge pressure for a **single-stage lobe compressor**?
100 kPa (14.5 psi)
## Footnote
Two-stage compressors can achieve higher pressures.
26
What are the advantages of the **lobe compressor**?(3)
* Compact design
* No inlet or discharge valves
* Produces even flow of oil-free air
## Footnote
These features make it suitable for various applications.
27
What do **rotary screw compressors** feature?
Two intermeshing rotors contained within a close-fitting casing
## Footnote
The male rotor has convex lobes, while the female rotor has concave flutes.
28
What is the typical speed range for **rotary screw compressors**?
3000 r/min to 12,000 r/min
## Footnote
A speed increasing gear is usually required between the compressor and the driver.
29
What is the maximum discharge pressure for a **single-stage rotary screw compressor**?
About 400 kPa (58 psi)
## Footnote
Multi-stage designs are used for higher pressures.
30
What are the advantages of the **rotary screw compressor**?(4)
* Compactness
* Vibration-free operation
* Smooth flow
* No suction or discharge valves
## Footnote
They can be designed to be oil-free.
31
What is the term used to describe compressors that use blades or vanes to give **velocity** and then **pressure** to the air?
Dynamic compressors
## Footnote
Dynamic compressors include centrifugal and axial flow types, with centrifugal being the focus here.
32
What type of compressor is similar in operation and construction to a **centrifugal pump**?
Centrifugal compressors
## Footnote
They consist of an impeller that rotates at high speed inside a volute-shaped casing.
33
In a centrifugal compressor, where is the air drawn in from?
The center or eye of the impeller
## Footnote
The air is discharged at the impeller periphery with high velocity due to centrifugal force.
34
What is the purpose of the **volute-shaped casing** in a centrifugal compressor?
To convert velocity into pressure
## Footnote
After the air passes through the impeller, it is discharged in a radial direction.
35
What additional component may be present in centrifugal compressors to aid in pressure conversion?
Stationary ring of diffuser vanes
## Footnote
These vanes help convert kinetic energy to potential energy due to pressure.
36
What is a **single-stage centrifugal compressor**?
A compressor with a single impeller
## Footnote
It can compress atmospheric air to a pressure of about 300 kPa.
37
What type of compressor is used for higher pressures than a single-stage compressor?
Multi-stage compressor
## Footnote
It has several impellers arranged in series on a common shaft.
38
Centrifugal compressors are commonly used for **large volume, low-pressure applications** due to their advantages of:(3)
* Simple and rugged construction
* Low maintenance requirements
* Oil-free air supply
## Footnote
Their efficiency is lower than positive displacement types and they are not suited for low capacity work.
39
What type of drivers are commonly used with centrifugal compressors installed in buildings?(2)
* Electric motors
* Reciprocating type internal combustion engines
## Footnote
Centrifugal compressors require high speeds, necessitating increasing gears.
40
What are **intercoolers** and **aftercoolers** used for in air compressors?
* Cooling the air between stages of compression (intercoolers)
* Cooling the air after compression (aftercoolers)
## Footnote
They are usually shell and tube type heat exchangers.
41
What is one reason for cooling the air in compressors?
* To remove water vapour and oil vapour
## Footnote
Cooling allows condensation, which can then be drained from the coolers.
42
What is the function of **intercoolers** in terms of efficiency?
To increase the efficiency of operation
## Footnote
This reduces costs associated with air compression.
43
What type of cooling is typically used in **air-cooled** compressors?
Air-cooled type
## Footnote
It uses a finned pipe through which the compressed air passes.
44
What should intercoolers be provided with for safety?(3)
* Safety valve
* Pressure gauge
* Thermometer on the compressed air side
## Footnote
A thermometer on the cooling water side is also recommended.
45
What is the function of an **aftercooler** in a compressed air system?
To cool compressed air and remove moisture and particles
## Footnote
The aftercooler uses counterflow cooling for efficiency and may include a cyclone separator.
46
What does the **cyclone separator** do in an aftercooler?
Removes moisture and other particles from the air stream
## Footnote
It is positioned after the aftercooler to enhance air quality.
47
In an aftercooler, the cooling water flow is _______ to the air flow.
counter
## Footnote
This counterflow concept yields more efficient cooling.
48
What is the purpose of an **air receiver** in a compressed air system?(3)
* Acts as an air reservoir
* Dampens pulsations in discharge pressure
* Allows moisture and oil particles to settle out
## Footnote
The air receiver is a pressure vessel that helps maintain consistent air pressure.
49
What are the specifications for air receivers according to the **ASME Code**?
Must conform to Section VIII, Pressure Vessels
## Footnote
This ensures safety and reliability in pressure vessel design.
50
List some components that an air receiver is typically fitted with.(5)
* Safety valve
* Pressure gauge
* Drain valve
* Inspection openings
* Fusible plug
## Footnote
These components are essential for safe operation and maintenance.
51
What should be done before inspecting an **air receiver**?
Thoroughly ventilate the interior
## Footnote
This prevents the buildup of carbon monoxide gas, which can be hazardous.
52
What is the role of **check valves** in a compressed air system?
Prevent high-pressure air from blowing back into the compressor
## Footnote
Check valves allow air to flow in one direction only.
53
What instruments should be connected to the delivery side of an air compressor?(2)
* Pressure gauge
* Thermometer
## Footnote
These instruments help monitor and maintain proper operating conditions.
54
What is the purpose of **pressure regulators** in a compressed air system?
To maintain required air pressure higher than that supplied by the compressor
## Footnote
Approved relief valves should be used to relieve pressure in case of a malfunction.
55
What are the **three methods** used to control the compressor output or capacity?
* Start and stop control
* Variable speed control
* Constant speed control
## Footnote
These methods help maintain a constant pressure in the system and suit load requirements.
56
In the **start and stop control** method, when does the compressor shut down?
When little or no air is required by the system
## Footnote
This method uses a pressure switch to sense the pressure in the receiver.
57
What are the **cut-in** and **cut-out** pressures in the start and stop control method?
* Cut-in: 650 kPa (94 psi)
* Cut-out: 750 kPa (109 psi)
## Footnote
The span between these values is 100 kPa.
58
What is the purpose of a **bleed valve** in the start and stop control method?
To bleed pressure off the piston prior to startup
## Footnote
This prevents the driver from starting under a high load.
59
List the methods by which the **bleed valve** can be operated.(5)
* Oil pressure
* Centrifugal force
* Mechanical linkage
* Electrical signal
* Manual manipulation
## Footnote
These methods ensure proper operation of the bleed valve during startup.
60
In **oil pressure startup unloading**, what happens when the compressor comes to rest?
The oil pressure dissipates to zero, opening the bleed valve
## Footnote
This allows air pressure within the cylinder(s) to exhaust to atmosphere.
61
How does **centrifugal force startup unloading** work?
A weighted device attached to the crankshaft closes the bleed valve as the shaft reaches speed
## Footnote
The weights fly outwards, acting to close the bleed valve.
62
What is the function of the **mechanical linkage startup unloading** method?
A pressure switch opens and closes the electrical circuit to the electric driver
## Footnote
This method is popular on smaller machines.
63
In **electrical signal startup unloading**, what controls the bleed valve?
An electrical signal opens the circuit to the solenoid valve
## Footnote
This method is typically used for larger machines that run constantly.
64
What does the **variable speed control** method do?
Increases or decreases compressor speed according to system demand
## Footnote
This is done by regulating the steam or fuel supply.
65
In **constant speed control**, how is the output from the compressor varied?
By using a pilot unloader
## Footnote
The compressor drive runs at a constant speed at all times.
66
List the four ways a **pilot unloader** may operate.
* Hold cylinder inlet valves open (reciprocating type)
* Close compressor intake line (dynamic type)
* Open a bleed valve to atmosphere (large dynamic type)
* Open a by-pass valve back to the compressor intake
## Footnote
These methods are seldom used due to energy inefficiency.
67
What are some **conditions** that a typical two-stage compressor might have an automatic shutdown device for?(8)
* High lubricating oil temperature
* High intercooler temperature
* High discharge air temperature
* High discharge air pressure
* Low lubricating oil pressure
* Low lubricating oil level
* Excessive vibration
* Cinder lubricator stopped
## Footnote
These conditions ensure the safety and proper functioning of the compressor.
68
What is the required **dew point** for compressed air used in plant instrumentation?
-40°C
## Footnote
This low moisture content is essential for proper functioning of instrumentation.
69
What are the two classes of **sorbents** used for moisture removal in compressed air?
* Adsorbents
* Absorbents
## Footnote
Adsorbents can achieve -40°C dew point air delivery, while absorbents achieve only 20°C dew point depression.
70
Name three examples of **adsorbents** used in air drying.(3)
* Silica-gel
* Activated alumina
* Molecular sieves
## Footnote
These materials attract water vapor to their surfaces for moisture removal.
71
What happens to the **temperature** of the dryer bed during the condensation of water vapor?
It raises due to the release of latent heat
## Footnote
This is important in larger systems located in humid climates.
72
How is the **adsorbent dryer bed** regenerated in automatic systems?
* Heated with a small purge of air
* Purged with hot dry air (150°C)
## Footnote
This process drives off the accumulated water.
73
What is the maximum dew point achievable with **absorbent systems**?
20°C
## Footnote
This is usually insufficient for instrument air but adequate for air tools and process applications.
74
What is the function of a **refrigeration dryer** in compressed air systems?
Cools the compressed air stream to condense water vapor
## Footnote
Dew points of -25°C are achieved, but these systems are bulky and energy-intensive.
75
List the functions of **lubricating oil** in an air compressor.(5)
* Prevent wear
* Reduce friction
* Remove heat
* Reduce corrosion
* Provide sealing
## Footnote
Proper lubrication is crucial for compressor performance.
76
What are the two main sections of **compressor lubrication**?
* External lubrication
* Internal lubrication
## Footnote
External lubrication does not contaminate the air, while internal lubrication is applied to compression zone components.
77
What is the typical temperature at the point of **maximum compression** in a compressor cylinder?
About 90°C (194°F)
## Footnote
In exceptional circumstances, temperatures may rise as high as 225°C (437°F).
78
What should be done before starting a compressor regarding **cooling water**?
Turn on the cooling water for cylinder jackets and heads
## Footnote
This is essential for preventing overheating.
79
What can cause a sudden change in **temperature readings** of cooling water?
An irregularity in the action of the discharge valves
## Footnote
Frequent temperature readings are important for monitoring compressor health.
80
What is the consequence of maintaining **higher pressures** than necessary in a compressor?
Higher temperatures
## Footnote
This can indicate cylinder valve malfunctions.
81
What is the role of the **safety valve** on an intercooler?
To prevent excessive pressure buildup
## Footnote
This is crucial for maintaining safe operational conditions.
82
What is the importance of **intake air cleanliness** for a compressor?
It affects the operation of the compressor and the extent of repairs needed
## Footnote
Impurities in the intake air can lead to increased wear and maintenance costs.
83
What must be removed from the intake air before it enters the **cylinder of the compressor**?
Impurities
## Footnote
Filters are used to ensure clean air enters the compressor.
84
From where should air be drawn to ensure cleanliness for a compressor?
As clean a source as possible outside the engine room
## Footnote
This helps maintain the integrity of the compressor's operation.
85
What effect does **abrasion** from lubricating oil and dust have on a compressor?(4)
* Causes wear
* Necessitates early replacement of parts
* Leads to shutdowns
* Increases labour charges
## Footnote
Abrasion can significantly impact the longevity and efficiency of compressor components.
86
What forms behind the **piston rings** due to sticky accumulations?
Hard deposits
## Footnote
These deposits interfere with the free action of the rings and impair the piston seal.
87
What factors influence how often **air filters** need cleaning?(4)
* Local conditions
* Type and capacity of the filter
* Volume of air handled
* Amount of dust in the atmosphere
## Footnote
These factors determine the maintenance schedule for air filters.
88
What is the effect of a **clean filter** on airflow?
Imposes very little restriction on the flow of air
## Footnote
Maintaining clean filters is crucial for optimal compressor performance.
89
What should be consulted to determine when a filter needs cleaning?
The manufacturer of the particular filter in use
## Footnote
They provide guidance on the correct cleaning methods and maintenance schedules.
90
What is a **pump** used for?
To transfer a liquid from one place to another by imparting energy to the liquid
## Footnote
Pumps have evolved into various types, sizes, and applications.
91
List the **common applications** of pumps in the power industry.(5)
* Fuel
* Lubricating oil
* Engine coolant
* High pressure hydraulic fluid for power steering
* Hydraulic pump for brakes
## Footnote
Pumps are employed in numerous locations for various purposes.
92
What types of materials can pumps move?(3)
* Molten metals at high temperatures
* Cryogenic materials at low temperatures
* Liquids at varying pressures
## Footnote
Pumps can generate pressures from barely perceptible to extremely high.
93
What is the power requirement range for pumps?
From a few watts to nearly 75 megawatts
## Footnote
Pumps can supply quantities from one drop per day to four billion litres per day.
94
What is the function of a **boiler feed water pump**?
Supplies the boiler with feed water against existing pressure
## Footnote
Essential for maintaining boiler operation.
95
What does a **fuel oil pump** do?
Pumps fuel oil to the burners in oil-fired boilers
## Footnote
Critical for the operation of oil-fired heating systems.
96
What is the purpose of a **lubricating oil pump**?
Circulates oil to the bearings of machines like turbines, pumps, or compressors
## Footnote
Ensures proper lubrication and functioning of machinery.
97
What is another name for a **circulating water pump**?
Cooling water pump
## Footnote
Used to pump water through heat exchangers like condensers or oil coolers.
98
What is the role of a **chemical feed pump**?
Pumps chemicals into boilers or as process pumps
## Footnote
Small capacity units are used for precise chemical dosing.
99
What does a **fire pump** supply?
Water to plant fire lines
## Footnote
Essential for fire safety in industrial plants.
100
What is the function of a **domestic water pump**?
Supplies water to plant washrooms and other domestic needs
## Footnote
Important for maintaining hygiene and sanitation in facilities.
101
Define **Static Discharge Head**.
Vertical distance from the centre line of the pump to the free surface of the water in the discharge tank or to the highest elevation of the discharge piping, whichever is greater.
## Footnote
This measurement is crucial for understanding pump performance.
102
What is **Total Static Head**?
Vertical distance from the surface of the source of supply to the surface of the water in the discharge tank or to the highest elevation of the discharge piping, whichever is greater.
## Footnote
It is the sum of static suction lift plus static discharge head.
103
Define **Static Suction Head**.
Distance from the free surface of the supply tank to the centre line of the pump.
## Footnote
This is important when the source of supply is above the pump.
104
What is **Total Head** in pump systems?
The sum of static and dynamic head required to move the water from the source of supply to the point of discharge.
## Footnote
The power required to drive a pump is determined by the amount of liquid pumped and the total head.
105
Define **Static Suction Lift**.
Distance, measured vertically, that the intake of the pump is placed above the surface of the water.
## Footnote
This occurs when the pump is located above its source of supply.
106
At an altitude of 1100 metres, the atmospheric pressure is equivalent to approximately _______ metres of water.
9.1 metres
## Footnote
Atmospheric pressure decreases with altitude, affecting pump performance.
107
What is the approximate atmospheric pressure at sea level?
101.3 kPa or 760 millimetres of mercury.
## Footnote
This pressure is equivalent to the pressure exerted by a column of water 10.34 metres high.
108
Centrifugal pumps should ideally be placed _______ the water supply.
close to or below
## Footnote
This is due to their poorer suction compared to piston or plunger pumps.
109
What factors can prevent a pump from achieving its maximum lift?(2)
* Friction in the pump and piping
* Leakage past the piston or plunger and valves
## Footnote
These factors contribute to the practical limitations of pump performance.
110
What are the **common types of pumps** used in the power industry?(3)
* Reciprocating pumps
* Centrifugal pumps
* Rotary pumps
## Footnote
Pumps are classified according to their method of operation and performance.
111
What type of pump is a **reciprocating pump**?
A positive displacement pump
## Footnote
It uses the reciprocating motion of pistons, plungers, or diaphragms to move the liquid.
112
List three applications of **reciprocating pumps**.
* Chemical feeding
* Small, high-pressure boiler feed pumps
* Fuel oil pumps
## Footnote
Reciprocating pumps are used for low volume, high-pressure applications.
113
Define a **centrifugal pump**.
A pump that uses centrifugal force to develop velocity in the liquid
## Footnote
The velocity is then converted to pressure when the liquid velocity decreases.
114
What happens to kinetic energy in a **centrifugal pump**?
It decreases, and pressure increases
## Footnote
This conversion occurs as the liquid velocity decreases.
115
Name the types of **centrifugal pumps**.(5)
* Volute
* Diffuser
* Axial flow
* Mixed flow
* Regenerative
## Footnote
The regenerative pump is not truly a centrifugal pump but is included in this classification.
116
Describe the construction of a **volute centrifugal pump**.
The liquid is drawn into the center of the impeller and discharged into the volute casing
## Footnote
The volute casing has an increasing cross-sectional area approaching the pump discharge.
117
What is the purpose of **stationary diffuser vanes** in a centrifugal pump?
To make the conversion from velocity to pressure more effective
## Footnote
They are installed around the rim of the impeller.
118
What shape does the casing of a **volute centrifugal pump** have?
Nautilus shape
## Footnote
This is in contrast to the concentric or round casing of a diffuser centrifugal pump.
119
What is the effect of the combination of centrifugal force and pressure in **diffuser pumps**?
It accounts for the total pressure developed
## Footnote
This occurs as the velocity of the liquid decreases.
120
What type of pumps are **rotary pumps** classified as?
Positive displacement pumps
## Footnote
Rotary pumps transfer pockets of liquid from low-pressure to high-pressure sides.
121
How do **rotary pumps** operate?
Transfer pockets of liquid
## Footnote
They move liquid from low-pressure to high-pressure sides where pockets are emptied.
122
Name some common types of **rotary pumps**.(3)
* Gear pumps
* Lobe pumps
* Sliding vane pumps
## Footnote
These types vary in design and application.
123
What is another name for a **gear pump**?
Spur gear pump
## Footnote
Gear pumps convey pockets of liquid to the discharge side.
124
What is the maximum pressure that **gear pumps** can handle?
10,000 kPa
## Footnote
This pressure rating indicates their capability in various applications.
125
In **lobe pumps**, how is the liquid transferred?
Around the outside of rotating lobes
## Footnote
The lobes are synchronized by external gears.
126
What is the function of the **sliding vanes** in sliding vane pumps?
Conform to the changing proximity of the pump casing
## Footnote
This allows for the transfer of pockets of liquid.
127
What happens to the size of the pockets in a **sliding vane pump** as the vanes rotate?
Decreases and increases
## Footnote
This change allows for liquid to be expelled and new liquid to fill the void.
128
What safety measure should be installed in the discharge line of **positive displacement pumps**?
Pressure relief
## Footnote
This prevents excessively high pressures that could damage the pump or piping.
129
What is **cavitation** in the context of pump operation?
When a pump is located above the source of supply, negative pressure can produce pockets of air or steam, causing damage to the pump internals
## Footnote
The shock waves from collapsing pockets can damage impellers or casing.
130
What does **priming** mean in relation to pumps?
Filling the pump casing and suction line with water or the liquid being pumped to remove all air
## Footnote
Priming prevents cavitational problems.
131
What is the function of **wear rings** in a pumping system?
Prevent leakage between the impeller and stationary pump parts, and reduce wear of the impeller and casing
## Footnote
Wear rings are inexpensive and easily replaced.
132
What do **compression packing shaft seals** do?
Reduce leakage around the pump shaft where it passes through the casing
## Footnote
They need periodic replacement due to deterioration from compression and inadequate lubrication.
133
What can **shaft misalignment** in pump bearings and shafts lead to?
Costly repairs or replacements
## Footnote
Proper alignment is crucial for day-to-day operations.
134
Before starting a **centrifugal pump**, what must be done?
It must be primed
## Footnote
Priming removes air from the pump head to prevent cavitation.
135
What materials are commonly used for **wear rings**?(2)
* Bronze
* Cast iron
## Footnote
These materials are favored for their durability.
136
Where are wear rings typically found in a **dynamic centrifugal pump**?
At the points where parts are very close together, such as between the impeller and the casing
## Footnote
They help maintain efficiency by minimizing leakage.
137
What is the purpose of **shaft sealing** in pumps?
To reduce leakage around the pump shaft where it passes through the casing
## Footnote
Shaft sealing is found on nearly all types of pumps, both dynamic and positive displacement.
138
What materials can be used for **compression type packing**?(6)
* Nylon
* Flax
* Teflon
* Lead
* Copper
* Aluminum
## Footnote
Packing is made from a wide variety of materials to suit different applications.
139
What is a **saturant** in the context of pump packing?
A lubricating material such as graphite or grease incorporated into the packing material
## Footnote
It helps to reduce friction and wear on the packing.
140
What is the function of a **lantern ring** in a stuffing box?
To distribute sealing water to the packing
## Footnote
It helps to prevent air leakage and lubricates the packing.
141
What should be done before **replacing pump packing**?
Shut down, isolate, and drain the pump
## Footnote
Ensure the pump motor switch is locked, fuses removed, and tagged with a 'Do Not Operate' warning tag.
142
What is the first step in the process of **replacing packing**?
Remove gland adjusting nuts and slide gland away from the stuffing box
## Footnote
Then remove all the old packing using a packing hook.
143
How often does **packing** need to be replaced?
Varies from months to several years
## Footnote
Depends on operating conditions, quality of packing, and installation care.
144
What should be checked on the **shaft** before replacing packing?
Conditions of the shaft or shaft sleeve
## Footnote
Any grooved or scored surfaces should be replaced to avoid damaging the new packing.
145
To determine the correct size of packing, what measurement should be taken?
Measure the bore of the stuffing box and subtract the diameter of the pump shaft
## Footnote
Divide the difference by two to find the thickness of packing needed.
146
What should be done if the packing is **slightly too large**?
Roll it out with a piece of pipe
## Footnote
Never flatten it with a hammer to avoid damaging the packing.
147
How should the **packing rings** be installed?
One at a time with a light coating of oil or grease
## Footnote
Each ring should be slid sideways over the shaft to prevent breaking.
148
What should be done after installing the packing rings?
Compress the packing slightly by tightening the gland nut
## Footnote
Initially, it should be just finger tight to allow for packing expansion.
149
What should the packing be allowed to do when the pump is first started?
Leak freely
## Footnote
After about twenty minutes, the follower should be gradually tightened to reduce leakage.
150
The method for installing packing is essentially the same for which types of pumps?(3)
* Centrifugal pumps
* Rotary pumps
* Reciprocating pumps
## Footnote
This indicates a standard procedure across different pump types.
151
What are the **advantages** of using **mechanical seals** over packing?(4)
* Require less maintenance
* Do not produce wear of shafts or shaft sleeves
* Reduce leakage to a minimum
* Can work under very high temperatures and pressures
## Footnote
Mechanical seals are preferred in many operational facilities like commercial buildings and public schools.
152
What is the **disadvantage** of mechanical seals compared to packing?
Greater first cost and longer downtime for replacement
## Footnote
When mechanical seals fail, the pump must be taken out of service for a longer period than with packing.
153
What are the two **general types** of mechanical seals?
* Rotating mechanical seal
* Stationary mechanical seal
## Footnote
Each type has a different configuration for sealing.
154
In a **rotating mechanical seal**, which component turns with the pump shaft?
Sealing ring
## Footnote
The sealing ring is held in place by a shell fastened to the pump shaft.
155
In a **stationary mechanical seal**, which component is held stationary?
Sealing ring assembly
## Footnote
The mating ring is fastened to the shaft and rotates with it.
156
What materials are commonly used for **sealing and mating rings** in mechanical seals?(5)
* Bronze
* Carbon graphite
* Ceramics
* Stellite
* Tungsten carbide
## Footnote
The choice of material depends on the type of liquid, temperature, pressure, pump speed, and seal design.
157
Fill in the blank: Mechanical seals must never run in a _______ condition.
dry
## Footnote
Running in a dry condition can cause the faces to become grooved and scored.
158
What are some **precautions** to take to care for mechanical seals?(3)
* Never run the pump in a dry condition
* Vent any air from the seal housing before startup
* Ensure adequate flow of quenching or cooling liquid
## Footnote
A squealing sound may indicate a dry seal.
159
What can cause a **leaking seal**? (5)
* Seal faces are scored or grooved
* Seal housing bolts are too tight
* 'O' ring gaskets are cut or nicked
* Misalignment of piping
* Excessive pump shaft vibration
## Footnote
These factors can lead to failure of the seal and leakage.
160
What are the **two general classes** of pump bearings?
* Shell or sleeve bearings
* Ball or roller bearings
## Footnote
Pump bearings support the shaft and allow it to rotate with minimal friction.
161
What is required for **perfect alignment** of pump and motor shafts?
The center lines of both shafts must be exactly in line
## Footnote
Perfect alignment is difficult to achieve and maintain during operation.
162
What are the two forms of **shaft misalignment**?
* Angular misalignment
* Axial misalignment
## Footnote
Angular misalignment occurs when shafts are at an angle, while axial misalignment occurs when shafts are parallel but beside each other.
163
What are the consequences of **misalignment** in shafts connected by rigid couplings?(5)
* Overheating
* Excessive wear of bearings
* Increased power consumption
* Shaft failure
* Vibrations and noise
## Footnote
Misalignment can lead to severe bending stresses in the shafts.
164
What are some causes of **misalignment**?(4)
* Poor installation or assembly
* Bearing wear
* Thermal expansion
* Flexing of shafts
## Footnote
These factors can cause misalignment even if the original installation was correct.
165
What is the purpose of a **flexible coupling**?
To protect machinery against the results of misalignment
## Footnote
Flexible couplings allow for a limited amount of angular and offset misalignment.
166
Fill in the blank: **Flexible couplings** can be divided into two basic groups: one with two rigid coupling flanges and a _______ and another with rigid coupling parts only.
flexible yielding member
## Footnote
The second group allows for flexibility through mechanical design.
167
What is an example of a **jaw type coupling**?
A coupling with a non-metallic spider-like insert
## Footnote
This insert may be made of synthetic rubber, laminated leather, or bakelite.
168
What is the purpose of **checking alignment** in pump couplings?
To ensure proper operation and prevent wear
## Footnote
Alignment can be checked using a straight edge or tapered feeler gauge.
169
What tool is used for a more accurate alignment measurement in pump couplings?
Dial indicator
## Footnote
It measures misalignment in thousandths of an inch.
170
What does **priming** a pump involve?
Filling the pump casing and suction line with liquid
## Footnote
Priming prevents cavitation and damage to the pump components.
171
What happens to the **wearing rings** if a pump runs dry?
They may seize due to lack of lubrication
## Footnote
Wearing rings require liquid to function properly.
172
Describe the **flooded suction method** for priming a pump.(3)
* Close the discharge valve
* Open the suction valve
* Open air vent valves until water flows
## Footnote
This method is used when the pump is below the source of supply.
173
What is a **foot valve** in the context of pump operation?
A flap type valve that allows water to enter but prevents backflow
## Footnote
It is essential for pumps located above the source of supply.
174
What is the purpose of the **foot valve** in a pump system?
Prevents water from escaping the pump
## Footnote
The foot valve is crucial for maintaining water in the suction line and pump casing.
175
In the first priming method, what is opened to allow water to flow into the pump?(2)
* Pale
* Vent valves
## Footnote
These components are essential for priming the pump from an external water source.
176
What indicates that the pump is ready for starting in the first priming method?
Water flows from the vent valves
## Footnote
This confirms that the pump casing and suction line are filled with water.
177
In the second priming method, what is the role of the **discharge valve**?
Shut to allow water from the discharge line to fill the pump
## Footnote
This method uses water from the discharge line to prime the pump.
178
What must be closed after water issues from the vents in the second priming method?(2)
* Vent valves
* Priming valve
## Footnote
Closing these valves indicates that the pump is ready for starting.
179
In the third priming method, what is used to exhaust air from the main pump casing?
Separate hand-operated priming pump
## Footnote
This method ensures that water fills the main pump casing and suction line.
180
What action is taken when water issues from the priming pump discharge?
Shut the priming pump valve
## Footnote
This step prepares the main pump for starting.
181
What is the function of the **air vent valves** in the priming process?
Allow air to escape during priming
## Footnote
This is crucial for ensuring that the pump and suction line fill with water.
182
What is the primary function of **lubrication** in machinery?
To separate surfaces moving in proximity to reduce friction
## Footnote
Lubrication involves interposing a liquid between moving surfaces to prevent contact.
183
List the **purposes of lubricants**.(6)
* Reduce friction
* Wear reduction
* Corrosion control
* Shock absorption
* Sealing
* Temperature control
## Footnote
These purposes help improve machinery operation and longevity.
184
What does **friction reduction** achieve in machinery?
It decreases the extra force required to move surfaces
## Footnote
Friction occurs due to interlocking hills and valleys on surfaces.
185
What is the effect of **wear** on machinery surfaces?
It can cause rougher surfaces and increased friction
## Footnote
Wear occurs when high spots on surfaces break away due to contact.
186
How does a lubricant help with **corrosion reduction**?
It forms a protective film on surfaces
## Footnote
Additives may be included to prevent acid formation from oxidation.
187
What role does lubrication play in **temperature control**?
It reduces heat produced by friction and can carry heat away from surfaces
## Footnote
Lubricants may be circulated and cooled in a heat exchanger.
188
Fill in the blank: The **force of friction** is the extra force required to move two surfaces that are ______.
in contact with each other
## Footnote
This force can be significantly reduced by using a lubricant.
189
What happens to surfaces when they are not lubricated and rub against each other?
They may cling or weld together
## Footnote
This increases the force required to move the surfaces.
190
What is the **pour point** in relation to lubricants?
The lowest temperature at which a lubricant can flow
## Footnote
It is one of the properties of lubricants.
191
What does the **flash point** of a lubricant indicate?
The temperature at which it can ignite
## Footnote
This is a critical safety property of lubricants.
192
What is the **neutralization number** in lubricants?
A measure of the acidity of the lubricant
## Footnote
It indicates the lubricant's ability to neutralize acids.
193
What is **carbon residue** in the context of lubricants?
The amount of carbon left after the lubricant is burned
## Footnote
This property helps assess the quality and performance of the lubricant.
194
What is the primary function of a **lubricant** in cases where surfaces come together with impact?
To absorb shock
## Footnote
An incorrect lubricant can result in noisy operation.
195
List the **six functions** of a lubricant.
* Minimum coefficient of friction
* Maximum adhesion to surfaces
* Physical stability under temperature and pressure variations
* Resistance to oxidation
* Resistance to emulsion
* Fluidity at low temperatures
## Footnote
The first two functions are the most important in the majority of applications.
196
Lubricants are divided into three general classes: **solid**, **semi-solid**, and **liquid**. What is the primary use of **solid lubricants**?
Used under conditions of high load and/or extreme temperatures
## Footnote
Solid lubricants are also used where other classes would collect dirt and debris.
197
What are some examples of **solid lubricants**?(3)
* Graphite
* Soapstone
* Molybdenum disulfide
## Footnote
Solid lubricants are effective in various applications.
198
What is the main advantage of using **grease** as a lubricant?
Less likely to leak away and can seal out dirt and water
## Footnote
Grease provides a permanent protective coating and requires less frequent attention.
199
What characteristics are required in a good **grease**?(5)
* Purity
* Consistency
* Chemical stability
* Thermal stability
* Tenacity
## Footnote
These characteristics are determined largely by the thickening agent used in manufacture.
200
What is the role of a lubricant in providing **sealing**?
To seal between pistons and cylinder walls or in rotating shaft seals
## Footnote
This function helps maintain the integrity of the system.
201
Fill in the blank: The **first two functions** of a lubricant are to separate bearing surfaces in order to reduce _______.
friction
## Footnote
This is crucial for the performance of machinery.
202
What are the **three general classes** of liquid lubricants?
* Mineral oils
* Fixed oils
* Synthetic oils
## Footnote
These classes categorize lubricants based on their origin and composition.
203
Mineral oils are produced from _______.
crude petroleum
## Footnote
They are the most commonly used class of liquid lubricant.
204
What are **fixed oils** also known as?
fatty oils
## Footnote
They are of animal or vegetable origin and include oils like lard and castor oil.
205
Name two types of **synthetic oils**.
* Polyglycols
* Silicones
## Footnote
Synthetic oils are suitable for high temperature service and can be fire-resistant.
206
Define **viscosity**.
A measure of the resistance of a liquid to internal deformation or shear
## Footnote
Higher viscosity indicates greater resistance and inability to flow.
207
How does **temperature** affect the viscosity of oil?
As temperature increases, viscosity decreases
## Footnote
Conversely, at low temperatures, viscosity increases.
208
What is the **Saybolt viscosimeter** used for?
Measuring the viscosity of an oil
## Footnote
It measures the time taken for a quantity of oil to flow through a tube.
209
What does a **high viscosity index (VI)** indicate?
Less change in viscosity with temperature
## Footnote
Oils with a high VI are preferred for automatic transmissions.
210
What does the **neutralization number** indicate?
The acidity of an oil
## Footnote
It helps determine when the oil should be replaced.
211
What is the purpose of **carbon residue testing**?
To determine the amount of carbon formed by oil at high temperatures
## Footnote
Excess carbon can interfere with engine and compressor components.
212
Name three types of **lubricating oil additives**.
* Anti-oxidants
* Detergent-dispersants
* Viscosity index improvers
## Footnote
These additives enhance the characteristics of lubricating oils.
213
What do **antifoam additives** do in lubrication?
Cause the collapse of air or vapor bubbles, preventing oil from foaming
## Footnote
Auto transmission oil contains much of this additive due to the action within the torque converter.
214
What is the function of **pour point depressants** in lubrication?
Lower the pour point of the oil, allowing it to remain fluid at low temperatures
## Footnote
This is highly applicable in refrigeration systems.
215
What do **corrosion inhibitors** do in lubrication?
Form a protective film on metal surfaces to reduce corrosion
## Footnote
This becomes critical when seasonal operation of equipment is a factor.
216
What are the **three types of bearings** widely used in industrial machinery?
* Shell, Sleeve, or Journal Bearings
* Anti-Friction Bearings
* Thrust Bearings
## Footnote
Each type of bearing serves a different purpose and has different lubrication requirements.
217
Define **boundary lubrication**.
Lubrication where surfaces are separated by only a film of lubricant
## Footnote
Occurs when the supply of lubricant is intermittent, allowing some metal-to-metal contact.
218
Define **fluid film lubrication**.
Lubrication where the film is thick enough to completely separate the surfaces
## Footnote
Also known as flood lubrication, occurs when the bearing clearance space is flooded with oil.
219
What are the **categories of lubrication** mentioned?
* Boundary lubrication
* Fluid film lubrication
## Footnote
Each category serves different lubrication requirements based on the type of bearing.
220
What is the role of **Power Engineers** regarding bearings?
Describe methods used to lubricate and maintain bearings, and causes of bearing failure
## Footnote
They are expected to have knowledge of lubrication and maintenance practices.
221
What are **shell (sleeve) bearings** typically constructed with?(2)
* White metal alloy lining (Babbitt)
* Cast iron or steel housing
## Footnote
Babbitt is suitable for lining because it deforms slightly to conform to load conditions.
222
What is the primary advantage of **Babbitt** in shell bearings?(3)
* Yields to conform to load conditions
* Soft enough to allow foreign particles to embed
* Corrosion resistant
## Footnote
Its softness allows it to 'wear in' to a smooth condition.
223
In what type of equipment are **journal bearings** commonly used?(2)
* Turbines
* Larger pumps
## Footnote
Journal bearings are used when the rotating mass is high.
224
What is required for **full fluid lubrication** in sleeve bearings?(2)
* Sufficient clearance around the shaft
* Oil supplied in the low-pressure area
## Footnote
This ensures effective lubrication during operation.
225
What is the **simplest method** of lubricating a bearing?
Hand-operated oil can
## Footnote
Suitable for small bearings requiring a few drops of oil every few weeks or months.
226
What is a **ring-oiled bearing**?(3)
* Lower part filled with oil
* Ring rides on the shaft
* Oil is dragged through the bearing slot
## Footnote
This method provides a continuous oil supply for pump and motor bearings.
227
What are **anti-friction bearings** composed of?(3)
* Moving components that roll
* Inner race
* Outer race
## Footnote
Rolling members can be balls, parallel rollers, barrel rollers, or tapered rollers.
228
What is the purpose of a **thrust bearing**?
To prevent a rotating shaft from moving in an axial direction
## Footnote
Thrust is a reactionary force created by machines like centrifugal pumps and steam turbines.
229
What is a **collar thrust bearing**?(2)
* Integral collars against bearing surface
* No room for oil wedge formation
## Footnote
Lubrication is of the boundary type, limiting the load it can carry.
230
What design allows for oil wedge formation in **thrust bearings**?
Bearing surfaces in the form of pads
## Footnote
Pads can tilt, allowing separation from the shaft collar.
231
Name the two types of **tilting pad thrust bearings** mentioned.
* Michell
* Kingsbury
## Footnote
These designs allow for better load handling and lubrication.
232
What is the **most satisfactory method** of cleaning roller and ball bearings?
Remove it from the shaft and dismantle it
## Footnote
This allows for thorough cleaning and inspection for signs of wear or failure.
233
When cleaning **without dismantling**, what should be done after removing the end covers?(3)
* Spray solvent into the bearing to flush out old lubricant and sludge
* Spray light lubricating oil into the bearing
* Replace end covers and refill with normal lubricant
## Footnote
This method can be used if dismantling is not possible or convenient.
234
What are the steps to clean a bearing by **dismantling**?(3)
* Remove the bearing from the shaft
* Clean all dirt from the outside of the bearing and shaft
* Avoid hammering on the inner or outer race
## Footnote
Care must be taken to avoid damage during dismantling.
235
What is one of the first signs of a **failing bearing**?
A rise in its operating temperature
## Footnote
Other signs may include unusual noises indicating excessive wear.
236
List the **causes of journal bearing failure**.(6)
* Improper viscosity of oil
* Improper bearing design
* Misalignment of shaft and bearing
* Loss of bearing metal due to corrosion or metal fatigue
* Loss of oil supply
* Oil temperature is too high
## Footnote
Excessive heat can develop in heavily loaded bearings.
237
How can excessive bearing temperatures be prevented?(3)
* A special cooling water channel in the bearing housing
* A special water coil immersed in the oil basin
* Circulating oil through an oil cooler before recycling
## Footnote
These methods help in cooling oil as well as grease-lubricated bearings.
238
What is a common cause of **anti-friction bearing failure**?
Metal fatigue
## Footnote
Even with proper maintenance, ball and roller bearings will eventually fail due to this.
239
What happens if a **poor quality lubricant** forms a hard mass within the bearing?
Rollers or balls may not be free to move, leading to wear
## Footnote
Hard pieces of lubricant can cause flaking and pitting on bearing surfaces.
240
What is **brinelling** in the context of bearing installation?
Indentation or nicks on the surface under the balls or rollers
## Footnote
This occurs when force is applied through the balls or rollers during installation.
241
What can cause cracking or splitting of the **bearing race**?(2)
* Forcing the bearing onto a shaft that is too large
* Applying force not squarely to the race during installation
## Footnote
Improper fitting procedures can lead to these issues.
242
What is **misalignment** of a shaft?
Misalignment occurs when a shaft is not properly aligned, causing uneven loading of the bearing
## Footnote
An example of misalignment is a driving belt that is too tight, leading to flaking of surfaces and excessive wear.
243
What is **false brinelling**?
False brinelling occurs in stationary bearings subjected to vibration, producing indentations in the surfaces in contact with the balls or rollers
## Footnote
It resembles true brinelling, which is caused by improper fitting.
244
What are the typical **operating temperature limits** for bearings?
Bearings can usually withstand operating temperatures up to 120°C (248°F)
## Footnote
Above this temperature, metal tends to soften, leading to excessive wear. Recommended maximums are generally 65°C to 70°C (149°F to 158°F).
Power Engineering Book 2 Part 2
flashcards
Decks in class (4)
# Cards
