BCIT 5th class boiler engineer quiz 2 Flashcards
When a closed expansion tank is used and the system is cold:
a. there will be no air in the tank.
b. the auto fill valve will maintain a system minimum pressure.
c. the tank level will be high.
d. the system should be manually filled.
e. the possibility of air in the system will be high.
b. the auto fill valve will maintain a system minimum pressure.
CH005 Q66
The automatic fill valve is simply a pressure reducing valve which keeps the system filled with water and maintains a set pressure in the system. If some water is lost from the system due to leakage, the system pressure will drop and the automatic fill valve will open to feed the water into the system from the city main or another source of water supply.
Heating boiler fittings:
a. are not regulated by ASME Codes.
b. must be registered by the chief engineer.
c. must be approved and registered by the regulating agency of the Province in which they are used.
d. may be used at the discretion of the power plant personnel.
e. do not require attachment of the manufacturer’s identity.
c. must be approved and registered by the regulating agency of the Province in which they are used.
CH005 Q01
Boiler fittings must comply with the requirements as set out in the ASME Code. In Canada, they must also comply with the rules in the CSA Standard B51 and the Provincial Boilers Acts. They must be approved and registered by the regulating agency of the province in which they are to be used. In order that valves and fittings are of the proper strength and material for the particular service for which they are used, it is necessary that they be clearly marked or identified.
Blowdown of a safety valve is defined as:
a. an increase in pressure that the valve opens.
b. the difference between opening and closing pressures.
c. lifting the test lever to blow steam out.
d. draining water from the safety valve.
e. the adjustment of the pressure setting of the valve.
b. the difference between opening and closing pressures.
CH005 Q26
The difference between the pressure at which the valve opens and the pressure at which the valve closes is called the blowdown of the safety valve. A threaded adjustable angular ring “G” (Figure) may be screwed up or down to vary the amount of port opening “F.”
The lowest water level at which a boiler can be operated without damage or overheating is referred to as the:
a. lowest operating level.
b. lowest working water level.
c. lowest visible water level.
d. lowest permissible water level.
e. lowest safe water level.
d. lowest permissible water level.
CH005 Q30
The lowest visible part of the water gauge glass shall be at least 25 mm (1 in.) above the lowest permissible water level recommended by the boiler manufacturer. With the boiler operating at this lowest permissible water level, there shall be no danger of overheating any part of the boiler.
The purpose of the small vent valve or cock located on top of the shell or on top of the water column on most boilers is to allow:
a. air into the boiler when the boiler is being filled with water.
b. water into the boiler when the boiler is being drained or cooled preventing the formation of a vacuum.
c. water to escape from the boiler when the boiler is being filled with air.
d. air to escape from the boiler when the boiler is being filled with water.
e. water to escape before the steam stop valve is opened during the warm-up period.
d. air to escape from the boiler when the boiler is being filled with water.
CH005 Q40
The vent valve is used for the following purposes:
It allows air to escape from the boiler when the boiler is being filled with water.
It allows air into the boiler when the boiler is being drained or cooled preventing the formation of a vacuum.
During the warm-up period of the boiler the air freed from the water by heating as well as the air that filled the steam space can be allowed to escape before the steam stop valve is opened.
The vent valve can also be used to check that the boiler is filling before the level rises to the gauge glass (air will be blowing out). In a similar manner the vent can be used to determine when the boiler has finished draining because air will no longer be drawn in.
When an electric probe type low-water fuel cutoff is employed on a heating boiler, it is important to:
a. vent off any hydrogen caused by electrolysis of the water.
b. check and clean the probes at regular intervals.
c. ensure the probe housing is properly insulated to prevent electrocution.
d. ensure the boiler is frequently blown down.
e. add salt to the boiler water to ensure good conductivity.
b. check and clean the probes at regular intervals.
CH006 Q03
It is necessary to check and clean the probes at regular intervals. Scale or sediment on the probes reduces or completely stops the current flow, resulting in a boiler shutdown. Note that these probes use alternating current and therefore electrolysis of the water does not occur and no hydrogen is formed.
A low-water fuel cutoff is fitted to a boiler to prevent:
a. damage to the radial stays in the steam dome.
b. the fire from shutting off too quickly and damaging the boiler.
c. damage to the boiler from over pressure.
d. shutting off the water when there is no fuel.
e. damage to the boiler from an overheated condition.
e. damage to the boiler from an overheated condition.
CH006 Q11
The main cause of heating boiler failure is overheating of the heating surfaces due to low water conditions. Normally, the water covering these surfaces will keep the temperature of the metal at a safe value. A low water level, however, allows the boiler metal temperature to increase to a point where it weakens and is not able to withstand the internal boiler pressure. This may result in the boiler metal rupturing and a massive release of pressurized steam and hot water. The ASME Code and CSA B51 require that every automatically fired boiler which is not under continuous attendance by a certified operator shall be equipped with an automatic low-water fuel cutoff device that automatically shuts off the fuel supply when the water level drops to about 25.4 mm (1 in) in the gauge glass.
The low-water cutoff can be tested by:
a. closing the steam discharge valve.
b. shutting off the fire.
c. opening the safety valve.
d. raising steam pressure.
e. shutting off the feedwater.
e. shutting off the feedwater.
CH006 Q09
Simulate a low water condition in the boiler by shutting down the feed pump and feedwater supply valve. On steam heating boilers, the valve on the condensate return line should be closed so the boiler will not get any replacement water. Allow the boiler water level to drop and note the level at which the cutoff switch shuts down the burner. The blowoff valve can be opened to hasten the operation. If the fuel is not shut off when there is about 25 mm of water remaining in the gauge glass, the boiler should be shut down and the low water cutoff repaired.
The low-water fuel cutoff:
a. controls the water level in the boiler.
b. shuts off the fuel and water supply.
c. shuts off the fuel if the water level is too low.
d. shuts off the fuel if the water pressure is low.
e. shuts off the water flow if the fuel pressure is low.
c. shuts off the fuel if the water level is too low.
CH006 Q10
The ASME Code and CSA B51 require that every automatically fired boiler which is not under continuous attendance by a certified operator shall be equipped with an automatic low-water fuel cutoff device that automatically shuts off the fuel supply when the water level drops to about 25.4 mm (1 in) in the gauge glass. This corresponds to a level approximately 76.2 mm (3 in) above the lowest permissible water level as specified by the manufacturer. The installation shall be such that the device cannot be rendered inoperative and can be tested under operating conditions.
The drain on a hot water boiler low-water fuel cutoff should be opened to flush out any build up of sediment:
a. annually.
b. monthly.
c. weekly.
d. daily.
e. each shift.
c. weekly.
CH006 Q04
Weekly: to check the low-water fuel cutoff mechanism, open the drain on the float chamber while the burner is in operation. The water level should drop enough for the float to open the mercury switch and shut down the burner. Carefully observe the water level at which the fuel cutoff switch shuts down the burner. If this cutoff level is not at or slightly above the lowest permissible level specified by the manufacturer, the low-water fuel cutoff should be serviced immediately or replaced if necessary.
Equalizing lines on a condensate receiver float chamber:
a. eliminate the need for a make-up level control valve.
b. keep receiver level equal to boiler level.
c. maintain equal flow of condensate to multiple boilers.
d. maintain make-up flow equal to condensate flow.
e. dampen level fluctuations.
e. dampen level fluctuations.
CH007 Q15
An externally mounted float controller feeder valve is preferred on most installations. The float chamber is attached to the receiver by equalizing lines which dampen the level fluctuations in the chamber resulting in a smooth flow of make-up water.
If the feed water check valve on a steam heating boiler fails to close, steam pressure could force the boiler water back into the return line, causing an unsafe water level. To prevent this, many boilers are fitted with a:
a. stop valve.
b. Hartford loop.
c. electric feeder valve.
d. high pressure limit switch.
e. combination low-water fuel cut off and feeder valve.
b. Hartford loop.
CH007 Q07
In older, small steam heating systems the condensate from the various parts of the heating system is piped to a common condensate return line or return main which feeds the condensate directly back into the boiler by gravity. The condensate is fed into the boiler through a return or Hartford loop. If the condensate return line would be directly connected to the feed connection in the lower part of the boiler, the possibility would exist that the steam pressure would force the boiler water back into the return line should the check valve fail to close, and the water level in the boiler could drop below the safe minimum level. The Hartford loop prevents this. The return line is connected to the loop at the height of the lowest safe water level. At that level the heights of the water in the boiler and in the loop will be equal and the steam pressure above the water in boiler and loop will be the same. Since water height and steam pressure in both boiler and loop are balanced, no water can be forced out of the boiler and sufficient water will cover the heating surfaces to prevent overheating.
At normal boiler steaming rates, the condensate receiver should contain water equivalent to the water evaporated by the boilers in:
a. 30 minutes.
b. 60 minutes.
c. 2 hours.
d. 4 hours.
e. 8 hours
a. 30 minutes.
CH007 Q18
An important requirement of a well-designed boiler feedwater system is a condensate receiver of adequate size together with a reliable method of makeup water supply to the receiver. An undersized receiver may cause loss of condensate, while an unreliable makeup feeder could result in boiler shutdowns due to low water conditions if the boilers are not equipped with feeder valves.
As a general rule, the size of the receiver should be sufficient to hold a volume of condensate equivalent to the water evaporated by the boiler in a 1/3 to 1/2 hour period at normal load. The smaller sized receiver may be used when the condensate returns easily, as in heating systems used in high-rise buildings. In systems extended over a large area (factories, warehouses, etc.), condensate return will be lengthy and the larger size tank should be used.
Heating plants with multiple boilers often have:
a. separate condensate receivers.
b. feed water pressure regulating valves for each boiler.
c. individual feed water systems.
d. a common feed water control valve.
e. independent boiler feed water control from a header.
e. independent boiler feed water control from a header.
CH007 Q08
In multiple boiler heating plants, the control of the water level in each boiler is independent from the other boilers but the feed water is usually supplied through a common feed line by a single pump. When one of the boilers requires water, its float operated control switch closes, energizing the motorized valve in the feed water branch line to the boiler. As soon as this valve reaches the open position, it closes an attached pump starting switch, and the condensate starts flowing from the receiver to the boiler. When the water in the boiler reaches its maximum level, the pump control switch opens the circuit, the motorized valve closes and the pump stops.
In heating plants with multiple boilers that are supplied from a single condensate receiver, all boilers commonly share a single:
a. boiler feed pump.
b. water column and gauge glass.
c. drum level control valve.
d. burner.
e. low water fuel cutoff.
a. boiler feed pump.
CH007 Q10
In multiple boiler heating plants, the control of the water level in each boiler is independent from the other boilers but the feed water is usually supplied through a common feed line by a single pump. This pump supplies water to a header that supplies all the boilers. Individual feeder valves on each boiler control the level of water in that boiler.
When a combination low water cutoff and feeder valve is used to control water level in a boiler, the code requires that:
a. the device is installed at the lowest safe water level.
b. the device be fitted with a gage glass.
c. a second low water fuel cutoff device is installed.
d. isolation valves be installed on the steam and water connections.
e. the feeder valve open before the low water cutoff device is activated.
c. a second low water fuel cutoff device is installed.
CH007 Q01
Float operated low-water fuel cut-offs are often combined with a valve assembly that is used to control the flow of feed water to the boiler. A cut-away view of this combination cut-off is shown in Fig.
Since control of the feed water supply is now the primary function of the cut-off device, a second cut-off is again required by code.
Which of the following controls would you expect to find on a low pressure steam boiler?
1. Operating pressure control.
2. High limit temperature control.
3. High limit pressure control.
4. Operating temperature control.
a. 3 and 4 only.
b. 1, 2, 3 and 4.
c. 2 and 4 only.
d. 1 and 3 only.
e. 1 and 4 only.
d. 1 and 3 only.
CH008 Q27
There are four distinct methods of burner operation control, they are:
1 **On-Off Control** - The burner fires at a constant rate which is sufficient to maintain boiler pressure or temperature at full load. When operating at less than full load, the burner is shut off when the upper pressure or temperature limit is reached and it is lit up again when the pressure or temperature drops to the lower limit. Thus the burner operates on an on-off cycle. This type of control is the simplest and is commonly used on low capacity boilers. However, it has the disadvantages that the pressure or temperature swings between the upper and lower set limits and that the boiler will not operate at maximum efficiency unless fired continuously. 2 **High-Low Control** - Two firing rates are available with the rate used depending on the boiler load. Operation with this type of control is more efficient than with the on-off control and pressure or temperature fluctuations are smaller. 3 **Modulating Control** - The firing rate is continuously adjusted to match a varying boiler load. The boiler pressure or temperature is maintained at a constant value and operation is most efficient. 4 **High Limit Control** *(High Steam Pressure Fuel Cut-Off)* - This control is used to shut down the fuel supply in the event of too high a steam pressure. This will help prevent a possible explosion.
On a multi nozzle boiler the high fire nozzle will:
a. be ignited by an independent pilot flame.
b. be in operation on start up.
c. operate continuously when steam demand exceeds capacity of low fire nozzle.
d. operate regardless of where the manual over-ride switch is set.
e. respond to electrical resistance.
c. operate continuously when steam demand exceeds capacity of low fire nozzle.
CH008 Q12
When steam demand is higher than the amount of steam produced by firing the low fire nozzle, the operating limit control will keep the low fire nozzle in continuous operation but the high-low fire control will now come into action and start the high fire nozzle(s) when pressure drops to 72 kPa, the cut-in point of this control. The pressure will then rise and when it reaches 86 kPa, the cut-out point, fuel supply to the high fire nozzle(s) is shut off again. Thus, at higher loads, the low fire nozzle is in operation continuously but the high fire nozzle(s) will be on on-off cycle and the operating pressure will vary between 72 kPa and 86 kPa.The high fire nozzle(s) will only be in continuous operation when steam demand equals or exceeds maximum boiler output.
When a lead-sulfide cell is used in a flame scanner it is sensitive to:
a. the presence of carbon monoxide in the flame.
b. infrared radiation.
c. furnace temperature.
d. visible light.
e. ultraviolet radiation.
b. infrared radiation.
CH009 Q09
Infrared Scanner: The scanner illustrated in Fig. containsa lead-sulphide cell which reacts to infrared rays.The cell is a semiconductor whose electrical resistance decreases instantaneously with an increase in the amount of infrared light from the main burner or pilot flame. Fluctuation of its resistance produces a fluctuating voltage across the cell. This voltage, called the “flame signal”, is amplified sufficiently by an electronic amplifier to hold an electromagnetic switch or flame relay in closed position.
When testing a gas burner with flame scanner, the scanner is removed and the main gas valve should trip closed within:
a. 1/2 second.
b. 4 seconds.
c. 6 seconds.
d. 10 seconds.
e. 15 seconds.
b. 4 seconds.
CH009 Q03
Gas Burner With Electronic Flame Scanner (Photoelectric Cell)Method 1: same as (Gas Burner With Electronic Flame Rod and Interrupted Pilot) below
Method 2:
1. Remove the scanner from its sighting tube and cover it. Note the time it takes for the automatic gas valve on the main burner supply to close. This should take no longer than four seconds.
2. If the test is successful, reset the controls, light the burner, and verify correct operation. Gas Burner With Electronic Flame Rod and Interrupted Pilot1. With the main burner in normal operation, close the main gas cock. Note the time it takes for the automatic gas valve to close. This should take no longer than four seconds.
2. If the test is successful, open the main gas cock, relight the burner, and check the burner for correct operation.
With automatic gas-fired boiler programmed control, the normal firing period begins approximately
a. 105 seconds after FD fan starts.
b. 75 seconds after FD fan starts.
c. 60 seconds after FD fan starts.
d. 47 seconds after pre-purge.
e. 10 seconds after pilot extinguishes.
a. 105 seconds after FD fan starts.
CH090 Q10
105: End of starting cycle. Beginning of normal firing period. Timer motor stops. Burner and blower remain in operation until heat demand is satisfied and operating control reaches its cutout point.
During the start-up of a boiler equipped with an automatic control system and flame scanning device, the manual fuel supply valve
a. must be closed before ignition.
b. can be opened before the flame scanner sees a flame.
c. must be opened before ignition can take place.
d. can be opened any time during start up sequence.
e. should be open as soon as pilot valve opens.
c. must be opened before ignition can take place.
CH010 Q13
Before a steam or hot water boiler can be started by a programming control, the following conditions must be fulfilled: all manually operated valves in the fuel lines to the pilot and main burner must also be open…
Compare with the following extracted from startup logic which relates to the automatic valve:
End of purge period. Ignition energized. Pilot gas valve opens. Start of trial period. When scanner sights pilot flame, flame relay closes. Main gas valve energized, main burner lights. Start of main burner ignition trial period.
On automatic boilers, liquid-fuel manual valves should be opened
a. with the automatic main burner fuel valve.
b. after the automatic main burner fuel valve opens.
c. prior to pre-purging.
d. after pre-purge and just prior to pilot ignition.
e. immediately after completion of the pilot flame trial.
c. prior to pre-purging.
CH010 Q08
Before a steam or hot water boiler can be started by a programming control, the following conditions must be fulfilled: All manually operated valves in the fuel lines to the pilot and main burner must be open…
The function of a programming control is to:
a. regulate the fuel supply to the burner.
b. regulate fuel, air, and water supply to the boiler.
c. control the boiler blowdown rate.
d. regulate combustion controls during start-up.
e. supervise feedwater supply to the boiler.
d. regulate combustion controls during start-up.
CH010 Q07
The programming control includes safety features related to boiler start-up. If any part of the starting sequence is not properly completed, it terminates the start-up sequence and purges the furnace. In addition, it orchestrates a controlled shut down of the boiler when the pressure rises to the cut-out point or other interlocks take out the boiler.
If a shutdown occurs during normal firing of a boiler and the steam pressure is below the normal cut-out value, the problem could be:
a. ignition transformer failure.
b. the sensing line to the combustion air proving switch is plugged.
c. pilot flame trial failure.
d. high steam pressure limit switch tripped.
e. main flame trial failure.
b. the sensing line to the combustion air proving switch is plugged.
CH010 Q06
If shutdown occurs during firing, it may be caused by faulty interlock. Each time the operating control or a limit switch such as the low water fuel cut-off opens and shuts down the boiler, or when the power fails, the boiler will automatically start up again when the switch closes or power has been restored. In these cases the lock-out switch will not be actuated. When the air flow to the burner is established, the low air pressure switch is closed. If the low pressure switch opens during boiler operation it will shut down the boiler. By process of elimination, the only correct answer is that the air proving switch has failed although other interlocks could cause the same condition.
The actual pressures at which a boiler safety valve opens and closes are determined by the
a) try lever test.
b) blowdown test.
c) trycock test.
d) pop test.
e) lift test.
d) pop test.
CH005 Q22
By raising the steam pressure in the boiler to the value at which the safety valve is set to open, the operation of the safety valve and the exact pressure at which it opens can be checked. This is called the “pop test.”
A valve which allows flow in one direction but stops flow in the opposite direction is called
a) an angle valve.
b) a check valve.
c) a gate valve.
d) a safety shutoff valve.
e) a globe valve.
b) a check valve.
CH005 Q44
The check valve allows a flow of fluid in one direction and automatically prevents any flow in the opposite direction.
A steam heating boiler pressure gauge may be tested while the boiler is in service using
a) a hydraulic comparator.
b) a hydrostatic test set.
c) an inspector’s test gage.
d) a dead-weight tester.
e) a digital multimeter.
c) an inspector’s test gage.
CH005 Q09
The connection for the Inspector’s test gauge is a tee fitting with one branch plugged. To connect the test gauge, it is necessary to shut off the lever-handle cock, remove the plug from the tee, and attach the test gauge at this point. The boiler pressure gauge may be tested while the boiler is in service by connecting an accurate test gauge to the test connection and comparing the reading of the boiler gauge to that of the test gauge. This is done by the Boiler Inspector during a boiler inspection. However, this method only compares the gauges at the particular pressure at which the boiler is operating.
A steam boiler is blown down in order to
a) clean the soot and carbon out of the firebox and tubes.
b) test the rated relieving capacity of the safety valves fitted to the boiler.
c) locate the steam level.
d) lower the operating water level in the boiler.
e) discharge sediment and foam causing matter from the boiler.
e) discharge sediment and foam causing matter from the boiler.
CH005 Q46
During the operation of the boiler, any sediment which has collected in the bottom of the boiler may be blown out. Also, as steam is produced from the boiler water, most of the dissolved impurities do not pass off with the steam but remain in the boiler water. As a result, the water becomes highly concentrated with solids and may begin to foam and carry over. This concentration may be reduced by blowing out some of this heavily concentrated water through the blowoff connection and replacing it with feed water with a relatively low concentration of impurities.
It is mandatory to have a steam stop valve on a steam heating boiler whenever
a) the operating pressure of the boiler exceeds 103 kPa.
b) the boiler is equipped with a superheater.
c) more than one boiler is supplying a common heating system.
d) the steaming capacity exceeds 300 kg/hr.
e) solid fuel is being burned.
c) more than one boiler is supplying a common heating system.
CH005 Q36
It is not mandatory to install a steam stop valve on a single boiler installation. It becomes mandatory when more than one boiler is installed to supply the heating system.
A low-water cutoff which serves no other purpose
a) cannot be an electrical conducting type.
b) must be a normally closed switch.
c) must be of an automatic reset design.
d) must be a float activated switch.
e) cannot be equipped with isolation valves.
e) cannot be equipped with isolation valves.
CH006 Q13
Since the cutoff devices described previously are all mounted outside the boiler, either in a special chamber or in the water column connected to the boiler by piping, no shutoff valves may be installed in the connecting piping. (ASME Code, Section IV).
A low-water fuel cutoff switch should close the automatic fuel valve(s) when the water level is
a) 76 mm above the lowest permissible water level.
b) at the lowest permissible water line.
c) 2.5 cm above the lowest visible water level in the gauge glass.
d) at the lowest visible water level in the gauge glass.
e) 1 to 2.5 cm below the gauge glass bottom nut.
c) 2.5 cm above the lowest visible water level in the gauge glass.
CH006 Q07
To test a low water cutoff, simulate a low water condition in the boiler by shutting down the feed pump and feedwater supply valve. On steam heating boilers, the valve on the condensate return line should be closed so the boiler will not get any replacement water. Allow the boiler water level to drop and note the level at which the cutoff switch shuts down the burner. The blowoff valve can be opened to hasten the operation. The burner should be shut down when the level is approximately 1 cm to 2.5 cm above the bottom of the gauge glass.
The low-water fuel cutoff on a steam boiler should be completely overhauled
a) once every five years.
b) once every two years.
c) once every year.
d) once every six months.
e) only as necessary when the unit fails.
c) once every year.
CH006 Q05
Annually: the low water cutoff on high- and low-pressure steam boilers and water feeders on heating boilers should be dismantled annually by qualified personnel. It should be checked for any obstructions, and proper operation of all the parts must be verified. Any leaks in the connecting lines to the boiler should be repaired. Connecting lines must be inspected for sediment and scale, and cleaned if necessary.
A float operated mechanical low-water fuel cutoff has its switch separated from boiler pressure by
a) a vacuum chamber.
b) a flexible diaphragm.
c) a siphon.
d) packing.
e) a mercury envelope.
b) a flexible diaphragm.
CH006 Q08
The float inside the chamber, which follows the changes in water level in the boiler, is directly connected to an electric switch attached to the float chamber. The switch is separated from the water chamber by a flexible diaphragm which acts as a seal.
Match the type of a maintenance of a low-water fuel cutoff for a steam boiler with its required frequency.
____ routine checks for leaks and abnormal conditions
____ draining of a float chamber while the burner is in operation
____ dismantling the device
____ tripping the boiler by shutting off water supply
- daily
- weekly
- monthly
- annually
1 (daily) routine checks for leaks and abnormal conditions
2 (weekly) draining of a float chamber while the burner is in operation
4 (annually) dismantling the device
3 (Monthly) tripping the boiler by shutting off water supply
CH006 Q14
Daily
Make routine checks for leaks and abnormal conditions. Repair any defects immediately.
Weekly
To check the low-water fuel cutoff mechanism, open the drain on the float chamber while the burner is in operation.
Monthly
Simulate a low water condition in the boiler by shutting down the feed pump and feedwater supply valve. On steam heating boilers, the valve on the condensate return line should be closed so the boiler will not get any replacement water. Allow the boiler water level to drop and note the level at which the cutoff switch shuts down the burner.
Annually
The low water cutoff on high- and low-pressure steam boilers and water feeders on heating boilers should be dismantled annually by qualified personnel. It should be checked for any obstructions, and proper operation of all the parts must be verified. Any leaks in the connecting lines to the boiler should be repaired.
When a large volume of makeup water to a condensate receiver is sometimes required, a small float operated valve may be used as a pilot valve. When the smaller valve opens, water is dumped from a pilot line causing a pressure drop that
a) causes a second diaphragm operated valve to open.
b) shuts off the feed water pump to maintain the level in the condensate receiver.
c) starts up a second condensate pump.
d) activates a low pressure alarm to inform the operator.
e) shuts fuel off to the boiler before the water level becomes too low.
a) causes a second diaphragm operated valve to open.
CH007 Q17
City water is supplied on top of the diaphragm of the make-up valve and to the float controlled valve through a small diameter control line which has a needle valve to control the water flow. When the level in the receiver is normal and no make-up is required, the float control valve is closed. The full pressure of the city water will act on the diaphragm of the make-up valve keeping it closed. When the level drops slightly below normal, the float control valve will open slightly, bleeding some of the water out of the control line. With a restricted flow of water through the needle valve, the bleed-off will cause the pressure in the control line to drop which reduces the force on the diaphragm, allowing the make-up valve to open slightly. The lower the level in the receiver drops below normal, the more water the control valve will bleed out of the control line and the lower the pressure in this line will drop. This, in turn, allows the make-up valve to open more. Receiver with Float Controlled Hydraulically Operated Make-Up Valve.
When a boiler shuts down due to a low-water condition
a) it can be restarted by simply resetting the cutoff switch.
b) a manual reset switch must be used.
c) the feed water flow will also stop.
d) a prepurge will not be necessary.
e) level must be restored to above the cutoff line before the unit can be restarted.
e) level must be restored to above the cutoff line before the unit can be restarted.
CH007 Q06
The boiler cannot be started up again unless the water is raised above level C, the operating level of the cut-off switch.
The result of a condensate receiver which is too small could be
a) loss of make-up water.
b) unacceptably high steam pressures.
c) low make-up water flow rates.
d) loss of condensate to the sewer.
e) high boiler water level(s).
d) loss of condensate to the sewer.
CH007 Q13
An important requirement of a well-designed boiler feed water system is a condensate receiver of adequate size together with a reliable method of make-up water supply to the receiver. An undersized receiver may cause loss of condensate, while an unreliable make-up feeder could result in boiler shut-downs due to low water conditions if the boilers are not equipped with feeder valves.
In heating plants with multiple boilers that are supplied from a single condensate receiver the level is controlled in each boiler by separate feed water valves supplied from a common header.
True
False
True
CH007 Q11
In multiple boiler heating plants, the control of the water level in each boiler is independent from the other boilers but the feed water is usually supplied through a common feed line by a single pump. This pump supplies water to a header that supplies all the boilers. Individual feeder valves on each boiler control the level of water in that boiler.
It is common practice to have a backup water supply for heating boilers that opens to supply city water into the boiler when a low level condition occurs.
False
True
True
CH007 Q02
Besides the cut-off switch in the power supply to the burner, the low-water fuel cut-off device is also equipped with a second switch which controls the power supply to an electric valve in the city water supply line. When the water level in the boiler drops well below the normal level, but before the level is reached at which the cut-off switch opens the burner circuit, the float closes the second switch energizing the electric valve, which then opens to allow the flow of city water into the boiler. This arrangement is illustrated in Fig.
An electric feeder valve will
a) prevent a low-water trip.
b) open before the low-water cutoff level is reached.
c) require manual action to open.
d) open after the unit trips on low-water.
e) eliminate the need for a low-water fuel cutoff.
b) open before the low-water cutoff level is reached.
CH007 Q04
Electric Feeder Valve
Besides the cut-off switch in the power supply to the burner, the low-water fuel cut-off device is often equipped with a second switch which controls the power supply to an electric valve in the city water supply line. When the water level in the boiler drops well below the normal level, but before the level is reached at which the cut-off switch opens the burner circuit, the float closes the second switch energizing the electric valve, which then opens to allow the flow of city water into the boiler.
In a low gas pressure fuel shutoff switch, the primary element that is acted on by the gas pressure is a
a) leaf spring.
b) diaphragm or bellows.
c) switch.
d) bourdon tube.
e) pitot tube.
b) diaphragm or bellows.
CH008 Q19
Low Gas Pressure Fuel Cut-Off Switch
This safety control device works on the same principle as the low air pressure cut-off. If, for any reason, the pressure of the gas supplied to the burner drops below a minimum value, which indicates insufficient gas for safe combustion, the switch opens up, and the fuel supply is cut off. The switch in Fig. consists of a diaphragm or bellows with pressure from the fuel acting on its lower side and the opposing force of the spring acting on its upper side. If the pressure of the fuel drops below a safe level, the leaf spring will drop, opening the switch to the solenoid operating the gas valve. The valve then closes, shutting down the burner, preventing an explosive condition in the boiler due to an unstable flame.
Steam heating boiler firing is normally controlled by boiler pressure whereas hot water boilers are fired to control
a) furnace temperature.
b) hot water temperature.
c) combustion air flow.
d) hot water pressure.
b) hot water temperature.
CH008 Q01
The temperature of the liquid in the sensing bulb will closely follow the temperature of the water leaving the boiler. When the water temperature rises the liquid in the bulb will expand. The excess liquid passes through the capillary tube to the bellows which, in turn, expands moving the lever of the control. Depending on the type of control mechanism used, the lever will either open the control switch when the cut-off temperature is reached or it will reduce the firing rate by adjusting the setting of the modulating motor controlling the fuel and combustion air supply. The opposite happens when the temperature of the water leaving the boiler drops.
A flame detector that senses visible light and uses cadmium oxide cathode and a wire anode wire is called a
a) cathode ray tube photocell.
b) ultraviolet scanner.
c) rectifying photocell.
d) vacuum tube photocell.
e) infrared scanner.
c) rectifying photocell.
CH009 Q01
Rectifying Photocell: The rectifying photocell, shown in Fig. is also known as a “cad” cell. It consists of a glass vacuum tube containing a curved metal cathode made of cadmium oxide and an anode wire, all forming part of an electronic circuit.
When multiple thermocouples are used to detect flame they are connected in series to
a) monitor more than one flame source.
b) increase the sensitivity of the detection system.
c) generate a higher voltage.
d) provide a spare thermocouple in case one fails.
e) none of the above.
c) generate a higher voltage.
CH009 Q08
Thermocouple:
A thermocouple consists of two dissimilar wires welded together at one end to form a measuring or hot junction, while the opposite ends are connected to an electric circuit at the cold junction. When the hot junction is exposed to the heat of a flame its temperature is higher than that of the cold or reference junction. A small voltage is generated causing current to flow through the circuit. The voltage supply generated by the thermocouple is usually not more than 30 millivolts so its electrical power is not sufficient to operate the full control system. A transformer is used to provide sufficient power to operate the main fuel valve. By using a number of thermocouples connected in series, sufficient voltage can be generated to operate the fuel control system independently from any source of power. This system is often called a thermopile.
With programming control, operating pressure control will control the
a) gas pressure to the burner.
b) steam pressure in the boiler.
c) boiler furnace pressure.
d) water pressure to the boiler.
e) steam temperature in the boiler.
b) steam pressure in the boiler.
CH010 Q14
The programming control will keep the main burner in operation until the desired preset operating steam pressure or water temperature is reached. At this time, the operating control will open the switch causing the load and flame relay of the programming control to also open and close the main fuel valve.
When the steam pressure or hot water temperature drops back again to the cut-in point of the operating control, the control switch will close again. This energizes the master relay to start the timer, and the start-up sequence will be carried out again. Once the power supply to the boiler has been established and the starting switch has been closed, the operation of the boiler becomes fully automatic.
An interrupted pilot of an automatic boiler
a) must be manually ignited.
b) lights before the main burner and goes out with it.
c) burns continuously, like that in a home furnace.
d) is one which has been extinguished by a flame scanner.
e) lights, completes a trial, and extinguishes after a main flame is ignited.
e) lights, completes a trial, and extinguishes after a main flame is ignited.
CH010 Q01
When the main flame is established by the pilot flame, the ignition transformer and pilot gas valve are de-energized and closed, if an interrupted pilot is used.
On a boiler with high-low fire control, if the damper positioning switch is in the wrong position
a) nothing will happen when the manual start switch is closed.
b) a pre-purge will not occur.
c) the pre-purge period will last indefinitely unless the problem is corrected.
d) the burner will remain in low fire.
e) the damper motor may not operate.
d) the burner will remain in low fire.
CH010 Q09
Burner Stays on Low Fire.
Possible Cause: Boiler pressure above high-low fire control setting.
Remedy: Wait till pressure drops to where there is load demand.
Possible Cause: Damper positioning switch in wrong position.
Remedy: Check damper linkage.
Boiler furnaces are purged
a) to cool any glowing refractory.
b) so the programmer has time to verify permissiveness of interlocks.
c) to ensure burner refractory is dry.
d) to completely remove combustibles from the furnace prior to ignition.
e) so the operator has an opportunity to check fuel and water systems.
d) to completely remove combustibles from the furnace prior to ignition.
CH010 Q02
Purging a furnace means forcing a flow of air through a furnace for a set period of time when the burner is not in operation. The purpose of purging is to remove any combustible gases that may have collected in the furnace while the burner is not in operation, and which could cause a furnace explosion when the pilot is lit again. The amount of air passed through the furnace during a purge must be at least four times the volume of the furnace and flue gas passages.
With automatic oil-fired boiler programming control, the normal firing period begins approximately
a) 10 seconds after pilot extinguishes.
b) 44 seconds after FD fan starts.
c) 47 seconds after pre-purge.
d) 60 seconds after FD fan starts.
e) 75 seconds after FD fan starts.
d) 60 seconds after FD fan starts.
CH010 Q04
The bar graph shows an operating sequence of a programming control for an oil-fired boiler with on-off operating control, single nozzle burner, and direct spark ignition. The chart following the bar graph describes the events in the starting sequence.
