HC 221 heating and cooling systems Flashcards
1
Q
thermal comfort is affected by what things
A
-air temp
-humidity
-air movement
-heat loss/gain
-ratiation
2
Q
what is heat loss and gain caused by
A
conduction or radiation
3
Q
what will improve air quality in an HVAC system
A
-propper filtration
-ventalation
-humidity control
4
Q
what is convection
A
the transfer of heat by air currents OR water current. air temp huumididty and speed play factors
5
Q
what are the 3 ways heat is transfered
A
-convection
-conduction
-radiation
6
Q
___________ refers to heat transfered by natural currents. if the air is cool it absorbs heat from the skin and because its able to move the heat is then carried away
A
convection
6
Q
the amt of heat gained or lost by convection depends on what
A
-temoerature and humidity of the air and the rate that it moves
7
Q
heat gained or lost through ______________ loss required direct physical contact
A
conduction
8
Q
warm air can hold __________ moisture
A
more
9
Q
cold air heated will be ____________ dry
A
more
10
Q
____________ is the transfer of energy across some distance without a conducting or convecting medium
A
radiation
11
Q
what is absolute zero
A
the temperature that atoms stop moving (0 degrees kalivin) ( -273 degrees celicus)
12
Q
why does moist air carry more energy than dry air
A
-because of energy stored in the water vapour. takes more energy to raise a temoerature of a colume of ait that is moist than it does if the air is dry
13
Q
moist air feels warmer than dry air due to the extra _____ energy it contains
A
heat
14
Q
how is humidy measured
A
relative humidity (RH)
15
Q
does an RH of a given volume of air change if the temperature changes
A
yes
16
Q
RH __________ as the air is heated
A
drops
17
Q
RH __________ as the air is cools
A
rises
18
Q
for general human health what is the ideal relative humidity (RH)
A
30-70%
18
Q
RH levels _______________ during heating season for comfort and increase the________ during hot weather
A
increase
discomfort
18
Q
_______ RH causes irriatation in lings and throat
A
low
19
Q
RH also affects the build up of _________ electricity
A
static
20
Q
when does static energy builf up in relation to RH levels
A
when they are low
21
Q
static is not a problem if the RH is not less than ___________-%
A
45%
22
what can air quality be reduced by
-particles like smoke dust pollen
-chemical pollutants like gas
-oxygen depletion
23
how can you improve air quality
-controlling source of pollutants
-using filters
-replenish indoor oxygen supply
24
residential furnaces use extended plenums to distribute conditioned ____________- air to ducts and draw ______ air from the house back through the furnace
supply
return
25
combustion and ventalation air both have to come from ____________
outdoors
26
how is combustion air provided
-natural building leakage
-vents to outside
-combustion air ducts that are brought near the furnace but not connected to
-combustion air ducts that return to the plenum
27
older furances reply on _________--- for ventalation
natural draft
28
modern instilations (mid efficent) for burners have what for ventalation and combustion
-combusion air duct terminated beside the furnace AND a second ventalation air intake duct that is terminated in the return air plenum
29
what is a standing piolet ignition
-a continuously burning flame
30
in a mid-efficent furnacew when do vents need to be active
when the burner is running
31
what does the second heat exchanger do in a high-efficiency furnace
-cools the exaust gasses
32
what do secondary heat exchanger and drains have to made from on a high efficency furnace and why?
-corrosion resistant materia;
-condensate liquid is very high
33
__________ burners are closed systems with a dedicated combustion air intake line and a vent that isnt shared with any other appliances. what are these intake and vents made from?
high efficiency
plastic
34
what material is never used with high efficency furnaces
metal
35
what does a condensor unit do
-takes a gas and turns it into a liquid
36
can a Air conditioning compressor unit compress a liquid
no it would blow up and youd fuck it up
37
A compressor unit is linked to the A-coil by 2 copper lines. what do they do?
1. carrying high pressure liquid refridgerant from the condesor to the evaperator.
2. for the low pressure vaporuized refridgerant that is returned to the compressor
38
what happens when the compressor pumps refridgerant vapour into the condenser
-loses its excess heat and liquifies
39
the liquif refridgerant is delivered under pressure to the ____________ where it is released at a controlled rate
evaporatior
40
the air-conditioning unit has its own ______ volt supply but its controlled by a _______ volt cct from the thermostat
240v
24v
41
what is an HRV
heat recovery ventalator
42
what does the HRV do
-acts as the central exuast fan, but uses warm exaust air to preheat the incoming ventilation air
43
What does a energy recovery ventalator do? (ERV)
-transfers heat an dhumidity from one air stream to another
44
an air-conditioning system can be used to reduce both of what
-RH
-temperature
45
what does a de-humidistat do?
-used to start the ventilation fans where the humidity is too high
46
if humidity is too low due to building leakage what is used to bring the humidity up
humidifier
47
what happens without air circulation
hot air rises
cold air settles to the floor
48
what is the benifet to using the furnace fan as constant circulation
-air is constantly filtered
-reduction of cold drafts
49
where is an air filter on a furnace found
-between return air duct and fan chamber
50
what does a conventional media filter do best
-clean air well enough to protect the heat exchanger
51
what type of filter is the more efficent than a disposable
HEPA (high effiency media filters)
- trap a higher % of the airborn material
52
how do electronic air cleaners work
use a high voltage DC supply to charge a fine wire grid with one polarity and a set of collection plated with the opposite polarity.
-air passes throuhg at one polarity then is drawn to the collection plate because it has the opposite polarity
53
what air filter for a furnace is the MOST efficient
electrinuc air cleaner
54
when is an upflow furnace used
-in a basement where the cold air entres the bottom of the furnace and is blown out the top into the extended phlenum
55
when is a downflow furnace used
houses without a basement or mobile homes
- cold air return is taken to the top of the furnace and the conditioned air is blown out the bottom unto the plenum and into the distrubuting ducts
56
why do horizonal and downflow furnaces have more temoerature limits built into them
-more hotspots in different spots if the fan fails to operarte
57
why are propane fired furnaces different than natural gas
-smaller holes to reduce the gas flow into the burners
58
in a propane furnace the size of the holes depend what
the rate gas is burned
59
how do oil furnaces work
-have a "gun type" burner
-fuel pump and combustion air blower driven by a small burner motor
-blower creates air stream down the barrel of the burner gun and the pressurized fuel oil is fef into the centre of it by a nozel
-when transformer is energized it lights a spark to light the fuel and air mixture
60
what are heat pumps
reversible air conditioners
61
how does a heat pump work
during heating season the heat pump extracts heat from the outdoor air and releases it into the heat exchanger inside. heating elements used during defrost cycles
62
in a residental heating boiler system how is the system broken into
-several zones each with their own thermostat
63
what does each zone of a residential boiler system have
-a normally open contact called an end switch that is wired into the circulating water pump control
64
how do end switches for a residential boiler system work
-contacts are in //
-pump starts when the first zone valve opens
-shuts down when all the zone valves are closed
65
what is the burner controlled by in a residential hot water boiler system
an aquistat (responds to warer temoerature in the boiler)
66
advantages of hot water heating systems for residential
-building heated effectivley without stirrin gup allergens in ducts
-easier to zone than force air
-dont need a seperate water heater for water in the taps
67
disadvantages of hot warer heating systems in residential
- higher inital cost
-higher water bill
- NO SHARED EQUIPMENT FOR ADDING CENTRAL AIR CONDITIONING
- cant filter air
68
what do you use limit switches for
-dampers
-valves
69
for boilers what are limit switches used for
-high pressure limits, shuts down burner if pressure gets too high
-low water cut off, shuts down the burner if the water gets too low
70
what are on delay timer contacts
-have a delay period that starts with when the timer is activiated
71
what are off-delay timer contacts
-have a delay period that starts AFTER the timer is deactivated
72
what is an anticipator
-stores energy
-prevents swings in temperature by turnin gburner off slighly before set point is reached by anticiaptin git will be reached soon
73
what is aquistat
a thermostat that responds to changes in liquid temperaturs
74
what is a cut in/cut out switch
one will turn on the furnace and one will cut in/out
75
what is a differiential
control with a differential that is too narrow will short cycle equipment which reduces efficency of burners
76
direct spark ignition
electric spark to light the main flame and HAS NO PIOLET FLAME
77
what is a direct vent
directly vents the firnace outside
78
what is a fan control
-cycle the circulating air blower of a heateing unit like a furnace
79
What is flame roll out protection
-manual reset disk with a red button
-looks for flames where they shouldnt be and if there is flames where they shouldnt be it will shut down
80
what is a high limit or limit control
shuts off the furnace burner if a phlenum gets too hot
81
what is the hot surface ignition
-uses a high temperature electric heating element to light the burner
-safter than a piolet light because there is no spark and a slower heat time. NO PIOLET FLAME
82
What is an intermittent piolet ignition
-piolet lights and stays lit while the burner is running and shuts off at the end of each burner cycle and doesnt shut off untul the main burner is shut off
83
what is interuppted piolet ignition
-shuts off the piolet light when the burner is running
-uses a piolet flame to light the main burner and shuts the piolet off when the main flame is operating normally.
-the burner control lights the piolet first then uses it to light the main burner then shuts off and runs on the main burner alone
84
what is a PSC motor
acts as a current limiting reactance and then tapped to provide different operating speeds
85
what is a standing piolet ignition
uses a continuous piolet to light the main burner and stays lit. is no longer used in residential homes for saftey reasons
86
What is a thermocouple
- coupling of 2 dissimilar metals and when we heat them they create 30mV. used as a saftey shut off for standing piolets and gas burners
87
what is the output of a thermocouple
30mV
88
what is a thermopile
bunch of thermocouples together run on their own supply for a fan but doesnt need power unless running on a fan
-
89
what is the output of a thermopile
750mV
90
what is a thermostat
converts change in temoerature into an output signal
91
What is a vent limit
a temperature operated contact that monitors the temperature of the flue gas at the bent in a gas furnace. opens if temoerature is too high
92
what is the primary hazard with gas burning appliances
-failing to light the gas when its admitted to the burner
93
where is a thermocouple mounted
with the tip in the piolet flame
94
what happens to the thermocouple if the piolet goes out
it cools off and the saftey valve closes to shut off the gas
95
in standing piolet gas burners how does the saftey valve coil get reset
must be opened manually with a push-to-light button
96
how does a standing piolet gas burner work
to start the burner-manual valve must be turned to the piolet position and then the saftey valve opened with the push to light feature. button cant be released until thermocouple gets hot enough to hold the vavle open then it will keep running
97
when will the gas flow in a standing piolet gas burner
-In the PIOLEt position the push to lught feature can work byt the gas is shut off ahead pf the main burner valve
-once the saftey valve is open the gas can only flow to the piolet burner
-in the on position the manual valve is opnen=ed and the gas flow is controlled by the saftey flow anf the main valve
-as long as the saftey calve is open the piolet recueves gas and the main burner gets gas
98
when will the main valve open in a standing piolet firnace on a 24vac system
-thermocouople has proved a flame to the value of 30mV
-thermostat calls for heat
-high limit switch is closed
99
what happens if the high limit switch opens in a standing piolet firnace on a 24vac system
-control cct and transformer de-energize
100
when will the saftey valve close in a standing piolet firnace on a 24vac system
wgeb tge thermocouple senses flame of 30mV
101
when does the fan motor operate in a standing piolet firnace on a 24vac system
whyen phlenem gets to a rated temperature
102
what does a murcury switch have
-glass bulb with 2 small probes in one end and a blob of mercery inside
103
what does dial setting determine in a mercery thermostat
-initial tilt of the bulb and changes in temperature bend the bimetal and tip the bulb to the left or right
104
what does an adjustable series resistor called a heat inticipator do
acts as a switch in the gas valve cct
105
what would happen if there wasnt a heat anticipator
temp would overshoot the set point
106
the anticipator resistor is not a current limiting device it is a ____________
adjustable heater
107
in a heat anticipator increassinf the amt of the resitor that is in the cct will __________- the heat output and _____ the cycles
increase
shorten
108
What do the R,C,W,Y,G terminals mean on a heating and cooling thermostats
R-power
C-common
W-heat (gas valve)
Y-cooling
G-fan
109
power is supplied to the _______ terminal from one side of the crontrol transformer
R
110
the gas valve or burner control is connected to the terminal marked with _______
W
111
what is a fan center
a transformer with a relay to turn one speed to another
-called a control centre
112
if a combination fan/limit control is used what has to be done to the jumoer and why
-jumoer removed to isolate the limit from the fan control
113
if the limit for a standing piolet mV system is part of a fan/limit conteol what must be done to isolate the 2 systems
remove the jumper
114
what are advantages of a mV sytem compared to a 24V system
-can run during a power outage
115
in what ways are the saftey shut off valve in a mV system the same and diffrent as a 24V ac main valve
same- if piolet goes out the main gas valve doesnt get gas
different-different voltages used, 750mV and 24V
116
mv systems are bad for intermittent problems caused by poor connections whats the reason
-poor or loose connections
-voltage drops
117
what does a CAD cell do
senses light
118
a furnace oil burner cycles on and off according to the demands of the thermostat and the flame must be lit how often
lit every time the burner starts
119
how is an oil burner monitored
-automatic flame detector and the burner motor will shut off if there isnt a flame
120
what is a stack control
bimetal detector
121
how does a CAD cell work
changes its resistance when exposed to light, light from flame reduces resistance and the control cct usees that change to operate the flame relay
122
why must a CAD cell be stored in total darkeness prior to the burner startiing
any light leakage could interfere with the propper flame detection and cause a false flame
123
what is the 1K relay
main relay, shuts off gas valve
124
what is the 2k relay
flame relay or change when it sees flame
125
what does a line voltage high limit do
shuts down ebverytning on high limit
126
what does a thermostat control
controls power to the low voltage side of the burner control
127
what does an oil valve do
a solenoid valve that shuts off the fuel supply
128
what does the burner motor do
motor that operates the oil pump and combustion air blower
129
what does the ignition transformer do
supplies voltage to spark the electrodes to light the fuel
130
what does the control transformer do
supplies power to the control cctg
131
what happens if there is a false flame in an oil burner control
2k relay will be picked up and the 2kI NC will open if there is no flame detected it wont pick up
132
how does a power humidifier work
-picks up water as the sylinder rotates and picks up the water from the tray and the hot air passing through the wet foam picks up and adds more moisture.
-humidified air passes through furnace through the cold air return and is distributed through the building
133
How does an oil burner cct work
- thermostat calls for heat which energizes 1k
-Ik2 energizes rhw burner/ignition/oil valve
-Ik1 contact closes in // with 2K1
-burner lights
-light from flame reduces resistance in CAD cell which enrgizes 2K contact
-2k1 NC opens and 2k1 No opens which bypasses the ss heater to advoid lockout
-burner runs until meets the heat demands then de energizes K1 which deenergizes the system
134
the humidistat starts and stops at the ___________V humidifier motor
24V
135
Humidifiers usually connected to the main furnace fan control cct. When does the humidifier run?
-when the fan is running
136
why must electronic air cleaners have to be interlocked with the main furnace fan
they are only energized when the fan is running
137
what is a sail switch
has a lightweight paddle that extends to the air stream
-A pressure on the airflow switch uses direct or differential pressure to operate the contacts
138
how do programmable thermostats that steal power work
-steals power from the 24V cct without a connection to the 24V common
139
why arnt most modern or high end thermostats not enterchangable
custom electronic so interchange with conventional thermostats
140
Can a class 2 power supply be connected in series or parallel with another class 2 power supply?
no
141
what kind of cable do you have to use for heating devices
FT4 rated cable
142
for a gas furnace you need a diconnect or any arching/sparking devices within _________. For propane its _______
1m
3m
143
how do you remove a blower fan in a furnace
remove jumper cable which attaches the cct board to the furnace wirings
144
what happens if you dont propperly tighten the bolts on a blower motor
-mounts wont be able to absorb vibration witch will cause lots of noise
145
how often must you lubricate low energy efficent furnaces
once or twice each year
146
what happens if you over lubricate an electric motor
- excessive oil will accumulate and dust and dirt will stick to it which interfears with cooling an dshorterns the life of the motor
147
how tight should a blower motor belt tension be
one inch of movemebt
148
A large diameter motor pulley will drive the fan at a __________- speed without a change in the motor speed
higher
149
Gas supply to mid and high efficient furnaces comes through a __________
solenoid valve
150
Is a high efficient furnace condensing or non condensing
condensing
151
Is a mid efficient furnace condensing or non condensing
non-condensing
152
In a mid or high efficient furnace what happens if the exuast fan isnt running
gas shuts off
153
Is a service switch a disconnect
no
a breaker would be
154
what is an HSI element
hot surface igniter
155
what happens if you touch an HSI element with your hands
destroyed by chemicals on your hands
156
What can depressurization cause
gasses to spill back into the buildings
157
The safe limit for depresurizartion is ________kPa of negatice pressure
5
158
in a forced-air heating system what does the furnace fan and duct do. when does the furnace fan run
supply fresg air through the building
-runs when the exaust fan is operating
159
in a forced air heating system how is fresh air brought in
through an outdoor air duct that connects to the return air plenum of the furnace
160
in forced air heating systems does it need a seperate combustion air supply
yes
161
in a hot water heating system what does a supply fan with an outdoor intake do
provides fresh air
162
in a hot water heating system when does the supply fan run
when the exaust fan is on
163
in a hot water heating system what is used to distrubute fresh air to every room
ducts
164
if the burner is gas for a boiler there will be a __________ combustion air duct
seperate
165
what is the preferred fan speed
lowest one
166
what is the most common ignition system
electric spark that lights a piolet flame
167
What is an intermittent piolet
-ignited at the start of the burner cycle and burns continiously until the main burner is shut down
168
what is an inturrupted piolet control
lights the piolet, proves it with a flame detector and then lights the main burner then the piolet shuts off
169
What type of ignition do oil burners use
electrical sprak ignition
170
Resdiential oil burners use what as a light sensitive cell
CAD
171
What do commerical or industrial burners use for flame light detection
-infared
-rectifying photo cells
-ultra violet
172
Large burners have regulators byt they also monitor ______________-- to be sure its in the right limits
gas pressure
173
The contacts from the gas pressure switch are used as _______________- or limits in the main burner control
interlocks
174
what is an air proving contact
interlock or limit in the burner control cct
175
Residential and commercial forced air units use one or more_________to monitor the temperature of the heat exchanger and may have other limits to protect against high vent temperature
high limits
176
How are commercial forced air system divided
Separately controlled zones
177
How do you zone thermostats work
Operate a damper mounted into a duct
178
A hot water boiler has a high limit what does it do
Detects a dangerous over temperature. and a low water cut off that shuts the burner down. If the boiler waterfalls below the safe operating level.
179
What does a two stage gas valve do
Reduce the number of operating cycles
180
What is a pressure troll
Monitors and measures pressure of steam in a boiler
181
Why do steam boilers have a pressure operated high limit?
To protect against over pressure and low water cut off, to shut down the burner if the water level falls too low
182
What do auxiliary pumps do
Return the collected contensate.
183
What components does a boiler have
Pressure troll, water cut off ,water level control float.
184
What does a water level control do in a boiler
Used to control the boiler feed pump or feed water supply valve that adds returned condensate to the boiler to replenish the water that is continuously being boiled into steam
185
Why do residential burners with induced draft blowers have a brief purge delay?
To allow the boiler to exhaust any combustible gases that may be left in the heat exchanger
186
In a residential burner what happens after the pre purged period is over
A residential burner with a pilot will energize.
187
What are three types of burners
Atmospheric, natural draft, forced air.
188
How does the atmospheric burner work
Gas comes out and mixes with air and burns. It is not pressurized
189
How does a natural draft burner work
A fan blows air in the direction and gas is pushed and it ignites. The gas is released into the air flow and is pushed by a fan
190
How does a forced air draft burner work
The fan blows air and it's pressurized and it pushes into the air flow
191
Residential and like commercial style burners operate with an input of how many Btuh
400,000 or less
192
In residential and like commercial style burners what is the flame failure response time
No more than three minutes
193
In commercial style burners what is the B T U rating
Over four hundred thousand B T U
194
In commercial style burners what is the flame failure response
No more than 4 seconds
195
What do flame rectification (flame rods) react to. is it polarity sensitive
React to D C current
yes
196
What do rectifying photo cells which are visible light detectors what's the input what's the output? is it polarity sensitive?
A C input D C output
yes
197
Are u v detectors polarity sensitive
yes
198
Is an infrared which uses lead sulfide cells that are sensitive to infrared radiation Polarity sensitive and what does it react to
Reacts to more than just heat and is not polarity sensitive
199
What type of flame detector is not polarity sensitive
Infrared
200
when are Flame Rods used with what type of burners
Gas burners
201
a flame is an envolope of __________ gasses
ionized
202
How does a flame rectification or a flame rod work
-First the electronic circuit automatically pre-checks the flame rod and will not allow the burner to light if a false flame condition exists.
- Second the flame circuit is used as a rectifier instead of Just a high resistance conductor
- The DC component is in the range of a 2-4 micro amps. The AC portion is quite a bit higher but the electronic circuit ignores it. The DC signal is amplified and is used to energize a flame relay
-200VAC converts to 2-4 microAmps
203
The D C flame rectifier current is a good indicator of what
general health Of the flame rod circuit
204
How does a rectifying photo cell work
Once it sees the flame it will turn AC into DC.
- It's a small vacuum tube that has a large curved collector plate and a smaller second terminal. When the light strikes the material it emits electrons which results that the cell response to visible light like the flame rod
205
Why are rectifying photo cells not used for gas burners
The blue flame of the gas burner does not provide enough visible light
206
How does A UV flame detector work
There are two electrodes. The anode and the cathode. when the cathode is exposed to UV radiation it emits electrons that ionize the gas in the tube this causes the tube to fire and generate a visible glow inside the tube
207
How much do uv detectors be placed
Have to have a clearview of the flame but they must not be able to see the spark from the igniter because the electric Spark can be mistaken for a flame
208
Are u v detectors polarity sensitive
Yes
209
What type of cell does the infrared detector use
Lead sulfide cell
210
Is an infrared detector polarity sensitive
No
211
How does an infrared cell work
Detects a flame in a firebox that is glowing with radiant energy
212
What type of burners are non-programming used for
Lower B T U burners
213
What type of burners are programming burner controls used for
Higher B T U burners
214
How does a non-programming control Self check to protect against unsafe controller failures
Start self check or dynamic self check
215
How does a start self check system work in a non-programming control
Self check systems will refuse to start the burner if a flame or flame stimulating condition exists when the controller is first energized It basically checks for a flame
216
How does a dynamic self check system work in a non-programming control
It continuously monitors their internal circuits and will shut down on an internal failure. It's checking for flames while it started
217
In a non-programming control what is the sequence the burner motor, ignition transformer,. Pilot and main valves
Models with the pre purge have internal timers or plug in timer modules to provide this function models without preparation may require external perge times
218
In a non-programming control how does it monitor the flame and respond to flame failure
Each controller has a built in amplifier or a plug in amplifier. They can use recycling controllers or non recycling controllers
219
How do recycling controllers in a non-programming control work
they will attempt to relate the burner if there is still a failure while the burner is running used in smaller B T U units and in residential
220
In a non-programming control how does non-recycling controls work
They will lock out if a flame failure occurs when the burner is running they're used for higher BTU units like commercial and it starts at the beginning every time there's a flame failure
221
How are the limits for a non-programming controls connected
In series in the power supply ahead of the burner control
222
In a programming control why does it self check and why is it the first thing it does
Protects against unsafe controller failures
223
Why won't boiler start in the high fire
Too much gas and there started in low fire
224
Why are limits connected in a programming control
225
Why does the burner controller pre purge with the maximum air flow
Ensure the fuel combustion error are set to low fire before any ignition attempt
226
In a programming control what happens if you don't pre purge
Cause an explosion in the firebox. A programming controller provides a time to preparge to ensure that's done properly each time the burner is lit
227
A programming controller may also use a __________________- to provide timed main burner ignition
Interrupt pilot
228
What are the two relays used in the RA 890 controller?
Non-programming burner and recycling controller
229
what is a fire tube
Fire in the tube and the water is in the container
230
Most heating boilers operate at low pressure what is the P S I
Fifteen p s i or less
231
in a steam boiler what happens if there is an ineffective purge or an undetected flame failure
Can become an explosion in a fire
232
In a steam boiler what does the pre purge do
Get rid of dirty air or leftover gas from chamber
233
How does a two pass fire tube heating boiler work
Flame travels down a large central tube that is surrounded by water then the returns through a large number of smaller tubes arranged in a rows around it
234
What does the blank Section at the top of a steam boiler do
portion that only has steam in it
235
In a steam Boiler what happens as the water boils into steam
Feed water which is mostly condensate is added into the bottom of the boiler vessel.
236
In a steam boiler the pump Or valve is controlled by the what
Water level control (WLC)
237
What point in a boiler must the water never be allowed to drop
Can't be dropped so low that it exposes any of the Fire tubes if this happened these two would overheat and be damaged
238
The water level in a boiler is monitored by what
A low water limit called the water cut off (LWCO)
239
Why do all boilers need to have a low water cut off (LWCO)
To shut down the burner in case the water level falls too low steam boilers also need a water level control (WLC) that works in conduction with the pump or valve
240
In a boiler what does a water level control do
Controls the amount of water the boiler receives
241
What kind of controls are used for low water cut off
Float controls
242
The LWCO contact is normally _________ and the WLC is normally ______
-closed
-open
243
How is a low water cut off and a water level control adjusted
Independently
244
Probe controls depend on what complete a circuit from one probe to another
The conductivity of water
245
How does a probe operated water level control work
The water moisturize to the upper which is the shorter probe to energize the relay coil. This energizes the really and closes the seal in contact between the two probes. Both probes now in connected into the relay circuit the water level must fall below the tip of the lowest probe before it will be de-energized
246
How does a probe type low water cut off work
The burner controllers shut down immediately on failures such as an open limit. The energizes the main gas valve to eliminate any potential hazards. It will restart automatically when the limit contact closes again
247
What happens when you add a connection to blue in a two position mechanical valve actuator
Opens air and gas
248
What happens when you add a connection to white in a two position mechanical valve actuator
Closes air and gas
249
What is the acronym for a two position mechanical valve actuator
ARWOBC. Stands for add resistance white opens And blue closes
250
How does a two stage fluid power valve actuator work
When the solenoid valve is energized to close the oil return port operating the motor driven hydraulic pump will force oil into the diaphragm chamber. The diaphragm is driven downward to open the spring loaded valve. A limits which shuts off the motor when the valve is fully operated.
251
When the solenoid valve is the energized in a two stage fluid power valve actuator what happens
The oil returns from the diaphragm chamber into the motor case, and the valve closes
252
What is the sequence of operation in a two stage fluid power valve actuator
A C B
253
Can non-programming controls restart
yes
254
Can the programmable control restart
No it has to go through all the steps which makes it recycle
255
What are the four steps in a programmable control
Step one prepare \
Step two ignition
Step three running stage
Step four post purge
256
What is the purpose of a thermistor in a non-programming control
Delays 1k relay
257
What does the 2 k relay do in a non-programming control
Sentence Flame if it detects a flame it will open which will make it all de energized
258
what is the purpose of an LS heater
It locks out the circuit if it doesn't light properly and energizes an alarm
