Power Eng Theory Chapters 90-95 and 104-109 Flashcards
Sectional cast-iron boiler sections are connected with
a) push nipples
b) modules
c) Victaulic couplings
d) unions
e) threaded fittings
a) push nipples
Cast-iron boiler sections maximize heat transfer by
a) utilizing as few passes as possible
b) vertical firing
c) exposing as large a surface as possible to the hot gases.
d) utilizing an external furnace
e) using four push nipples per section
c) exposing as large a surface as possible to the hot gases
Boiler water legs
a) increase the heating surface
b) surround the furnace entirely
c) make water treatment less critical
d) support the boiler on concrete piers
e) make waterside maintenance easier.
a) increase the heating surface
Boiler sections are held together with
a) cap bolts
b) torque tubes
c) pipe unions.
d) tie rods
e) stays
d) tie rods
The ratio of heat released to heat transferred to boiler
water is known as
a) combustion efficiency
b) heating surface efficiency
c) boiler efficiency
d) section ratio
e) enthalpy transfer ratio
c) boiler efficiency
Most low capacity cast-iron boilers
a) cannot be site assembled
b) can withstand higher pressures
c) will pass through standard size doorways
d) are factory assembled as packaged units
e) require special foundations
c) will pass through standard size doorways
The steam and water spaces of a cast iron sectional boiler are connected by
a) tie rods
b) tie nipples
c) hydraulic jacks
d) steel studs
e) push nipples
e) push nipples
The steam and water spaces of a cast iron sectional boiler are held together by
a) cast iron pipes
b) push nipples
c) steel studs
d) tie rods
e) push studs
d) tie rods
In a vertical sectional boiler the sections are placed
a) one above the other
b) side by side
c) 45 degrees to each other
d) 90 degrees to each other
e) 180 degrees to each other
b) side by side
The sections of cast iron boilers are mainly designed to
obtain maximum
a) water space
b) steam space
c) water circulation
d) heat transfer
e) steam output
d) heat transfer
The fins cast on the flat surface of the sections of a cast iron sectional boiler are used for the purpose of increasing the
a) effectiveness of heat transfer
b) steam capacity
c) water capacity
d) water circulation
e) steam output
a) effectiveness of heat transfer
To prevent flue gases from escaping in a cast iron sectional boiler, the spaces between the sections are sealed with high temperature
a) silicon chalking
b) foam insulation
c) plastic insulation
d) putty
e) asbestos rope
e) asbestos rope
Heating boilers attain maximum efficiency only when they are operated
a) intermittently at 90% of the load
b) intermittently at half load
c) continuously at full load
d) continuously at half load
e) continuously at 75% of the load
c) continuously at full load
Modular cast-iron boiler water flow is
a) continuous through all modules
b) connected in series
c) intermittent, occurring only while the unit is firing
d) always vertically upwards
e) done without the use of headers or manifolds
a) continuous through all modules
In a cast iron modular heating boiler, the operation of the burner of each module is controlled by a __________ which starts or stops modules in sequence as load demand increases or decreases.
a) temperature sensor
b) step controller
c) thermostat
d) temperature transmitter
e) flow controller
b) step controller
A cast-iron boiler disadvantage is
a) it is subject to corrosion
b) its difficult assembly
c) its extremely high cost
d) its high ductility
e) its pressure limitations
e) its pressure limitations
A cast-iron boiler advantage is
a) its high factor of brittleness
b) light weight resulting in lesser foundation requirements
c) its ability to withstand high pressure
d) the choice of assembly location
e) their large capacity
d) the choice of assembly location
Cast-iron boiler capacity
a) is very large compared to steel boilers
b) can be increased by simply adding sections
c) cannot be increased once assembly is completed
d) is not a function of section numbers
e) can be increased by increasing section size
b) can be increased by simply adding sections
The reducing of oil into very small particles is termed
a) fluidization
b) fractionation
c) turbulence
d) atomization
e) distillation
d) atomization
Before atomization can occur, heavy oils are heated to
approximately
a) 203 degrees C
b) 95 degrees C
c) 115 degrees C
d) 75 degrees C
e) 150 degrees C
b) 95 degrees C
An air atomizing burner utilizes an air pressure of
approximately
a) 15 kPa
b) 150 kPa
c) 75 kPa
d) 95 kPa
e) 100 kPa
e) 100 kPa
An air atomizing compressor is usually
a) a variable displacement type
b) a centrifugal type
c) an axial type
d) a positive displacement type
e) a regenerative type
d) a positive displacement type
The capacity of a constant capacity mechanical atomizer is a function of
a) orifice size
b) pump speed
c) pump size
d) supply pressure
e) oil viscosity
a) orifice size
A modulating pressure atomizer has its return oil flow
regulated by
a) a modulating valve to the burner
b) a modulating valve in the return line
c) a solenoid valve in the return line
d) a temperature control valve to the burner
e) pump speed
b) a modulating valve in the return line
To which of the following oil burners is the oil supplied under high pressure?
a) mechanical atomizing burner
b) air atomizing burner
c) rotary cup burner
d) steam atomizing burner
e) multi-spud burner
a) mechanical atomizing burner
When using mechanical fuel oil atomization
a) 70 kPa steam pressure is required at the burner
b) 35 to 40 kPa oil pressure is required
c) high pump pressure is required
d) steam pressure is required to keep the bypass open
e) dry saturated steam or superheated steam should be used
c) high pump pressure is required
Oil burners can be divided into three classes:
- air and steam atomizing burners
- mechanical or pressure atomizing burners
- centrifugal or rotary cup burners
- atmospherical pressure burners
- gravitational pressure burners
a) 1, 2, and 3
b) 1, 2, and 4
c) 2, 3, and 4
d) 3, 4, and 5
e) 2, 3, and 5
a) 1, 2, and 3
The compressed air used as atomizing air in the air atomizing oil burner is also called
a) secondary air
b) primary air
c) pre-mixed air
d) pre-compressed air
e) post-copressed air
b) primary air
The two basic varieties of mechanical atomizing oil burners are:
- variable capacity burner
- constant capacity burner
- modulating burner
- stationary burner
a) 1 and 3
b) 2 and 3
c) 3 and 4
d) 1 and 5
e) 4 and 5
b) 2 and 3
A multi-burner cluster has secondary and tertiary nozzles ignited by
a) an igniter spark
b) an intermittent pilot flame
c) an interrupted pilot
d) the primary burner
e) a continuous pilot
d) the primary burner
When a greater than normal amount of combustible mixture is ignited the result may be
a) a boiler explosion
b) a puff-back
c) a negative furnace pressure
d) a too rapid boiler warm-up
e) liquid fuel entering the furnace
b) a puff-back
A fuel filter consists of
a) a cartridge
b) wool felt
c) three main parts
d) a Y-strainer
e) a canister
c) three main parts
Burner light oil supply pressure range is approximately
a) 50 to 100 kPa
b) 150 to 250 kPa
c) 300 to 550 kPa
d) 550 to 700 kPa
e) 700 to 850 kPa
d) 550 to 700 kPa
A relief valve is placed on the discharge of a fuel oil pump
a) because the pump is a dynamic type
b) so burner design pressure is not exceeded
c) so burner capacity is maintained
d) to prevent pump rupture
e) to prevent over-firing of the boiler
b) so burner design pressure is not exceeded
A time delay oil valve
a) opens when the pump starts
b) opens once ignition is verified
c) opens on flame failure
d) is located on the return line
e) is upstream of the pressure regulating valve
b) opens once ignition is verified
In order to prevent the possibility of a furnace explosion it is important that the furnace is __________ before the
igniter is energized and fuel is supplied to the burner
nozzle(s).
a) pre-heated
b) post-heated
c) purged
d) cooled
e) pressurized
c) purged
Intermediate and high fire burner nozzles have higher
capacities than the primary burner nozzle
a) to give greater firing variations
b) to prevent pressure surges
c) to prevent ignition puff-backs
d) because of the pump being of the positive displacement type
e) to allow better boiler warm-ups
e) to allow better boiler warm-ups
Oil flow rate to a modulating burner is regulated by
a) a return line modulating valve
b) a PRV on the burner line
c) pump speed
d) pump capacity
e) firing rate
a) a return line modulating valve
The minimum distance from furnace to oil storage tank is
a) 7 m
b) 5.2 m
c) 2.1 m
d) 4.7 m
e) 9.8 m
c) 2.1 m
Maximum static pressure in a fuel oil line is approximately
a) 10 kPa
b) 15 kPa
c) 80 kPa
d) 35 kPa
e) 70 kPa
e) 70 kPa
The main function of a gas burner is
a) atomization of the fuel
b) a source of ignition
c) provision of O2-fuel contact
d) regulation of the fuel flow
e) air flow control
c) provision of O2-fuel contact
An atmospheric burner has air entering around the burner which is termed
a) primary air
b) secondary air
c) atomizing air
d) combustion air
e) tertiary air
b) secondary air
The amount of pre-mix air to an atmospheric burner should be
a) 10 to 12%
b) 5 to 8%
c) 20 to 30%
d) 30 to 40%
e) 40 to 50%
d) 30 to 40%
A refractory burner disadvantage is
a) high initial cost
b) too much fuel preheat
c) low radiant heat
d) low combustion efficiency
e) overheating of boiler metal
a) high initial cost
A very popular packaged boiler gas burner is the
a) ring burner
b) non-articulated burner
c) post mix atmospheric burner
d) mechanical atomizing burner
e) cluster nozzle burner
a) ring burner
An atmospheric burner head which is very popular on heating boilers is the
a) refractory type
b) star type
c) ring type
d) rectangular type
e) ribbon ring type
d) rectangular type
When a gas fired burner is burning fuel properly
a) it will have a blue flame with short yellow tips
b) the furnace will pulsate
c) there will be no turbulence
d) it will have a long bright yellow flame
e) the induced draft fan can be shut off
a) it will have a blue flame with short yellow tips
Gas burners for heating boilers can be divided into two
general classes and they are the
a) pre and post turbulence burners
b) before and after burners
c) pre and post purge burners
d) pre and after mix burners
e) pre and post combustion burners
d) pre and after mix burners
The Venturi tube in the atmospheric burner mixing head has a
a) gradually decreasing cross-sectional area
b) gradually increasing cross-sectional area
c) sharply decreasing cross-sectional area
d) sharply increasing cross-sectional area
e) uniformly distributed cross-sectional area
b) gradually increasing cross-sectional area
__________ burner heads are most common for use in heating boilers.
a) Oval
b) Circular
c) Semi-circular
d) Triangular
e) Rectangular
e) Rectangular
One of the advantages of the refractory (gas) burner is the
a) low cost
b) gas and air mixture is thoroughly preheated before it
enters the furnace
c) flue gases are recirculated back to the furnace to
increase the furnace temperature
d) flue gases are thoroughly post-heated before they
leave the furnace
e) flame is directed to areas where it is needed the
most
b) gas and air mixture is thoroughly preheated before it
enters the furnace
The purpose of the deflector vanes in the centre of a ring (gas) burner is to
a) atomize the gas particles
b) increase the gas velocity
c) decrease the air velocity
d) promote turbulence of the gas and air mixture
e) increase the temperature of the furnace
d) promote turbulence of the gas and air mixture
One of the advantages of using natural gas as a fuel in a boiler is
a) that no storage space is required
b) the low cost
c) the abundance in supply
d) the portability
e) that no transmission lines are required
a) that no storage space is required
An intermittent pilot
a) lights the main flame then extinguishes
b) must be manually ignited
c) lights the main flame and remains on with it
d) remains on when the main flame extinguishes
e) lights a pilot flame then extinguishes
c) lights the main flame and remains on with it
The pilot burner for gas fired heating equipment can be:
- manual
- continuous
- intermittent
- interrupted
- automatic
a) 1, 2, and 3
b) 2, 3, and 5
c) 2, 3, and 4
d) 3, 4, and 5
e) 1, 2, and 5
c) 2, 3, and 4
The __________ pilot is most often used on small boilers.
a) interrupted
b) intermittent
c) automatic
d) manual
e) continuous
e) continuous.
Large capacity burners
a) require high flow on ignition
b) are very safe relative to puff-back
c) require only a small pilot flame
d) should have minimum flow on ignition
e) are too hazardous and not recommended
d) should have minimum flow on ignition
A hydramotor valve
a) opens and closes quickly
b) helps to prevent puff-backs
c) uses air as its working medium
d) should not be the last fuel valve to open
e) closes slowly
b) helps to prevent puff-backs
A solenoid type fuel valve
a) is held closed by fuel pressure
b) always opens rapidly
c) is held closed by electrical current
d) closes slowly
e) does not have positive shut-off
a) is held closed by fuel pressure
If the power is cut off to an automatic gas valve, the valve will be
a) closed slowly
b) closed immediately
c) closed slightly
d) closed half-way
e) opened widely
b) closed immediately
The advantage of a motorized (hydramotor) gas valve is that the valve opens __________ thus preventing “furnace puff”.
a) slowly
b) quickly
c) immediately
d) slightly
e) half-way
a) slowly
A function of a Bourdon tube gage hairspring is
a) return the tube to its zero position
b) keep the pointer on zero
c) eliminate backlash
d) return the pointer to zero
e) eliminate pointer linearity
c) eliminate backlash
An LP steam pressure gage range shall be between
a) 210 and 420 kPa
b) 300 and 450 kPa
c) 200 and 500 kPa
d) 210 and 460 kPa
e) 150 and 300 kPa
a) 210 and 420 kPa
An inspectors’ test connection
a) should be located upstream of a siphon
b) should be of 12.7 mm NPT size
c) is required on all boilers
d) shall be located adjacent to the gage
e) is not mandatory on LP boilers
e) is not mandatory on LP boilers
When installing a siphon it
a) must be perpendicular to the piping
b) must be dry
c) should be downstream of an inspectors’ test connection
d) should be first filled with water
e) shall be as close to the boiler as possible
d) should be first filled with water
An indication of a pressure gage not performing properly is
a) the needle fluctuating
b) the needle not returning to zero on depressurizing
c) a dial which rotates
d) a reading which is not the same as some other gage
e) the safety valve popping when gage reads normal
b) the needle not returning to zero on depressurizing
When using a dead weight tester, the effect of friction
a) is reduced by rotating the platform
b) will cause a higher than desired reading
c) is negligible
d) is eliminated with a lubricant
e) is compensated for mathematically
a) is reduced by rotating the platform
The working medium in the dead weight tester is
a) air
b) water
c) heavy oil
d) medium weight oil
e) alcohol
d) medium weight oil
An essential fitting between the boiler and the steam pressure gauge is
a) a check valve
b) a gate valve
c) a gage glass
d) a siphon
e) a steam trap
d) a siphon
A steam pressure gauge is graduated in
a) pascals
b) pascals per square metre
c) kilograms per square centimetre
d) kilograms per hour
e) kilopascals
e) kilopascals
The prime importance of boiler fittings are
a) economics
b) efficiency
c) safety
d) convenience
e) ease of operations
c) safety
All boiler fittings not properly or clearly identified should be
a) rejected
b) used for low pressure services only
c) used for low temperature services only
d) used for supplying low pressure water to softeners
e) accepted for a lower pressure or temperature rating
a) rejected
The purpose of the test connection on a boiler pressure gauge is to
a) unplug the siphon tube
b) test a sample of steam for purity
c) install the boiler inspector’s pressure gauge
d) inject live steam to the gauge
e) vent air from the pressure gauge
c) install the boiler inspector’s pressure gauge
As the boiler pressure increases, the bourdon tube of the pressure gauge will
a) tend to straighten
b) compress more
c) become less circular in cross-section
d) become smaller in diameter
e) tend to twist
a) tend to straighten
The cross-section of a Bourdon tube is generally
a) circular
b) round
c) cylindrical
d) spherical
e) oval
e) oval
An essential fitting between the boiler and the steam
pressure gauge is a
a) check valve
b) gate valve
c) gauge glass
d) siphon
e) steam trap
d) siphon
The purpose of the pipe siphon installed between the boiler and the pressure gauge is to prevent
a) air from entering the gauge
b) water from entering the gauge
c) hot steam from entering the gauge
d) air from entering the boiler
e) hot steam from entering the boiler
c) hot steam from entering the gauge
According to the ASME code, the scale on the dial of the steam gauge for a low pressure steam heating boiler shall be graduated to not less than
a) 210 kPa
b) 420 kPa
c) 510 kPa
d) 640 kPa
e) 720 kPa
a) 210 kPa
According to the ASME code, the scale on the dial of the steam gauge for a low pressure steam heating boiler shall be graduated to not more than
a) 210 kPa
b) 420 kPa
c) 510 kPa
d) 640 kPa
e) 720 kPa
b) 420 kPa
An LP steam boiler safety valve shall not be smaller than
a) 110 mm
b) 12.7 mm
c) 76 mm
d) 25.4 mm
e) 101.6 mm
b) 12.7 mm
In order to ensure a safety valve seats properly, it uses
a) seat rings
b) a huddling chamber
c) a blowdown ring
d) guides and bushings
e) a test lever
d) guides and bushings
The force of the steam pressure acting on the safety valve disc is a function of
a) disc area
b) huddling chamber volume
c) seat diameter
d) percent valve opening
e) blowdown ring diameter
a) disc area
The minimum blowdown of an LP safety valve is
a) 96% of the set pressure
b) 5% of the set pressure
c) 14 kPa
d) 2 kPa
e) 101.3 kPa
c) 14 kPa
Popping pressure of an LP safety valve may be adjusted
a) any amount
b) no more than the allowed blowdown
c) up to 5%
d) up to 7.5%
e) by anyone
c) up to 5%
The blowdown on a safety valve is adjusted by turning the
a) inspector’s seal
b) valve disc
c) adjusting nut
d) adjusting ring
e) valve seat
c) adjusting nut
What does the boiler inspector install to prevent tampering with a safety valve setting?
a) a restraining order
b) a gag
c) a seal
d) a plug
e) a cover plate
c) a seal
The lip on a safety valve
a) allows it to close slowly
b) is only required if the steam is superheated
c) supplies a drain lip for condensate to collect on
d) makes the valve stronger
e) allows it to “pop” open
e) allows it to “pop” open
A safety valve on a steam heating boiler must not be smaller than
a) 25 mm
b) 19 mm
c) 38 mm
d) 13 mm
e) 30 mm
d) 13 mm
According to the ASME code, steam heating boilers shall have one or more safety valves, adjusted and sealed to discharge at a pressure not exceeding __________ kPa.
a) 100
b) 101
c) 110
d) 103
e) 105
d) 103
According to the ASME code, the valve seat diameter of the safety valve on a steam heating boiler must not be smaller than
a) 12.7 mm (1/2 in.)
b) 25.4 mm (1 in.)
c) 38.1 mm (1 1/2 in.)
d) 50.8 mm (2 in.)
e) 63.5 mm (2 1/2 in.)
a) 12.7 mm (1/2 in.)
According to the ASME code, the valve seat diameter of the safety valve on a steam heating boiler must not be larger than
a) 25.4 mm (1 in.)
b) 38.1 mm (1 1/2 in.)
c) 50.8 mm (2 in.)
d) 63.5 mm (2 1/2 in.)
e) 110 mm (4 1/2 in.)
e) 110 mm (4 1/2 in.)
For a steam heating boiler, the safety valve shall be such that, with the fuel burning equipment installed and operated at maximum capacity, the pressure cannot rise more than ___________ kPa above the maximum allowable working pressure when all steam outlets are closed.
a) 103
b) 101
c) 100
d) 55
e) 34
e) 34
The safety valve shall be installed in __________ position and located in the highest practicable part of the boiler
proper.
a) the highest
b) the lowest
c) a mid
d) a vertical
e) a horizontal
d) a vertical
An LP safety valve lever test should be performed
a) weekly
b) semi-annually
c) monthly
d) daily
e) quarterly
c) monthly
LP boiler safety valves can be repaired
a) only when authorized by the inspector
b) by anyone qualified to do so
c) by a qualified boiler operator after permission from the inspector
d) by a licensed boiler operator
e) by only the manufacturer
c) by a qualified boiler operator after permission from the
inspector
An operator should check that a boiler safety valve will open at its set pressure by
a) sending for the inspector to bring his or her test gage
b) increasing the boiler pressure until the valve opens and noting the pressure on the pressure gage when the valve opened
c) putting a piece of pipe over the lifting lever and lifting the valve off its seat when the seat pressure is reached
d) connecting the boiler to an air compressor during shut down and raising the pressure in the boiler until the set pressure is reached
e) listening to the alarms of the set pressures
b) increasing the boiler pressure until the valve opens and
noting the pressure on the pressure gage when the valve opened
Testing the safety valve by means of the try lever method, is considered good practice when carried out on a
a) weekly basis
b) monthly basis
c) six monthly basis
d) yearly basis
e) bi-weekly basis
b) monthly basis
If a safety valve leaks after a try lever test, the operator
should
a) plug the safety valve outlet
b) reduce the boiler pressure
c) operate the try lever several times to blow away foreign material
d) fit a gag to the safety valve
e) reduce boiler pressure and call the team leader
c) operate the try lever several times to blow away foreign
If you found the safety valve on your heating boiler stuck in the closed position while the boiler was in operation, the best thing to do is
a) tap it gently with a bronze hammer to free it
b) reduce the boiler pressure and continue operating
c) report it to the shift team leader
d) shut down the boiler and repair or replace the safety valve
e) put the boiler on hand control and notify the inspector
d) shut down the boiler and repair or replace the safety valve
LP steam boilers must be equipped with a marker indicating the
a) maximum water level line
b) low water fuel cut-off line
c) lowest permissible water line
d) lowest visible water line
e) fireline
c) lowest permissible water line
A gage glass may be surrounded by a number of thin rods
a) when the boiler is a high pressure unit
b) to protect the operator from injury
c) to prevent cold draft damage
d) to protect the glass from damage
e) if the glass is attached to a water column
d) to protect the glass from damage
Quick-closing gage glass valves
a) prevent loss of water automatically should glass rupture
b) should be installed on all boilers
c) will not permit gage glass blowdown
d) are designed to prevent operator injury
e) require 90 degrees for full travel
e) require 90 degrees for full travel
A disadvantage of a gage glass safety-shutoff valve is
a) the glass cannot be blown down
b) it requires more maintenance
c) it cannot withstand high pressure
d) loss of water is not prevented
e) it makes gage glass replacement more difficult
b) it requires more maintenance
Should the steam line or water line to a gage glass become plugged with sludge
a) gage glass level will drop in both cases
b) gage glass level will drop in the first case and rise in
the second
c) gage glass level will remain where it was
d) the gage glass will read high
e) gage glass level will rise in the first case and drop in
the second
d) the gage glass will read high
Water column supply line crosses will
a) permit piping inspection
b) allow for piping cleaning and inspection
c) replace safety shut-off valves
d) be installed only on boilers not under continuous
supervision
e) prevent gage glass blowout
b) allow for piping cleaning and inspection
Gage glass rupture may be caused by
a) maximum allowable boiler pressure
b) a cold draft
c) a sudden pressure drop
d) warming the boiler up too quickly
e) improper boiler water treatment
b) a cold draft
When gage glass nuts are leaking
a) the gage glass should be replaced
b) they should be tightened immediately
c) new packing should be installed
d) the glass should be isolated and depressurized before tightening
e) they should be replaced
d) the glass should be isolated and depressurized before
When the water connection between boiler and gage glass becomes plugged, the water level in the glass will show a level after a while, that is
a) higher than the level in the boiler
b) lower than the level in the boiler
c) the same as the level in the boiler
d) fully filled
e) lower than the bottom of the sight glass
a) higher than the level in the boiler
The lowest visible part of the water gauge glass shall be at least __________ mm above the lowest permissible water level recommended by the manufacturer.
a) 25
b) 50
c) 75
d) 100
e) 125
a) 25
The ASME code states that each steam boiler shall have one or more water gauge glasses attached either directly to the boiler or to a water column by means of valve fittings not less than __________ mm pipe size.
a) 75
b) 51
c) 24
d) 13
e) 10
d) 13
On a multiple steam boiler heating system, a stop valve must be placed at each boiler outlet to
a) permit slower system warm-ups
b) allow boiler isolation from the system
c) prevent steam from entering another boiler
d) allow each boiler to supply only a part of the system
e) permit different system pressures
b) allow boiler isolation from the system
Boiler outlet valves are usually
a) gate valves because of their low resistance to flow
b) gate valves because of the ability to control flow
c) globe valves because of their throttling capability
d) globe valves because of their low flow resistance
e) installed in tandem
a) gate valves because of their low resistance to flow
An outside screw and yoke valve
a) is always a gate valve
b) readily shows its operating position
c) is difficult to lubricate
d) requires no packing
e) has a non-rising stem
b) readily shows its operating position
The quick closing valves on the water gauge requires only a/an __________ of a turn of the valve spindle to change the valve from the full open to the full closed position and viceversa.
a) eighth
b) quarter
c) one-third
d) fifth
e) half
b) quarter
The feedwater pipe, before it enters the boiler must be
fitted with a __________ valve adjacent to the boiler.
a) stop
b) gate
c) globe
d) check
e) plug
d) check