Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
55 Cards in this Set
- Front
- Back
|
Manifold pressure of gas flowing up to gas orfice |
3.5” wc |
|
|
What does venturi design of burner mean? And why is it used? |
1.Becomes larger as gas air mixture heads to burner ports 2. velocity is reduced increasing pressure, is called static regain, gives it adequate pressure to burn at burner ports |
|
|
What is the purpose of secondary air? |
Complete combustion process, only 30-50% of air needed for combustion is supplied in primary air. |
|
|
What controls amount of primary air? How is it set? |
1. Primary air shutter. 2. To the btuh rating of the burner, if lessened velocity is lowered in gas orfice lowering pressure |
|
|
What is partial pre-mixing? |
Some of air is premixed prior to combustion process |
|
|
What is a Bunsen flame? |
Blue flame, due to pre mixing |
|
|
What is a perfect flame? What are 2 imperfect flames? |
Blue but not too blue. Too blue is an oxidizing flame. Carbonizing flame is orange and means too much fuel |
|
|
What is flame lifting? And flashback? |
1. Too much velocity on flame front 2. Not enough velocity |
|
|
What can be caused by lifting flame? |
Aldehydes and carbon monoxide |
|
|
How to stop lifting flame? |
Usually you can just reduce primary air. |
|
|
What is cause of yellow tipping? And what can it result in? |
1.Not enough primary air 2. Carbon manoxide |
|
|
2 purposes of orfice |
1. Regulates flow rate through burner, set to btuh or kw input rate 2. Sends flow down center line of burner mixing tube. |
|
|
What should be used to clean orfice? |
Broom straw, wire brush bristle |
|
|
What is adjustable orfice? |
Needle inside adjusts to change opening of orfice. Used on gas ranges and adjustable burners |
|
|
Formula for orfice sizing. |
Flow rate (cfh) = btuh input / (1000 btuh/cf) |
|
|
How much to de-rate appliance in Calgary? |
4%, it is 4% for every 1000 ft above 2000ft, Calgary is at 3400ft |
|
|
How far should thermocouple be into pilot flame? |
3/8-1/2” |
|
|
What is a pilot stat? |
Also known as safety shut off valve, screws into gas valve and is connected to thermocouple it is responsible for shutting off gas if burner goes out. |
|
|
What is open circuit test thermocouple? And what is expected result |
1. Det voltage output of thermocouple (20-30mV) |
|
|
What is open circuit test thermocouple? |
1. Det voltage output of thermocouple (20-30mV) P. 178 |
|
|
What is a closed circuit test for thermocouple? And what is expected range? |
Tests that voltage is enough to hold valve in open position 10-15 mV P.179 |
|
|
What is drop out test? And expected range? |
Same as closed circuit but flame turned off and allowed to de-energize 2-4 mV |
|
|
What is drop out test? |
Same as closed circuit but flame turned off and allowed to de-energize 2-4 mV P.181 |
|
|
Flame failure response test? |
Timing pilotstat to drop out placing unit in safety shut down condition. 1-1.5 min P. 181 |
|
|
What is Aprox voltage of thermopile? |
750 mV |
|
|
In a closed circuit test. What happens if the value is really low or really high? |
1. If low thermocouple needs to change, since it has high internal resistance 2. If high check pilot stat coil or power unit. Because it has high operating resistance |
|
|
What is a drop out test? |
Done same way as closed circuit test. Turn off pilot. Should drop at 2-4 mV |
|
|
What is flame failure response test? Time? |
1.Time it takes for power unit to shut down. 2. Should be about 1 minute to a max of 1.5 mins |
|
|
Pilot turndown test. How long after gas valve clicks on should main burner light at max? |
4 seconds |
|
|
How is heating anticipator set? |
By amperage drawn by the coil of the gas valve |
|
|
What protects the valve coil from shorting out? |
Since heating anticipator is wired in series with valve coil, it would burn out the anticipator 1st |
|
|
Diaphragm gas control valves which are mostly used on residential equipment are mainly opened and closed by? |
Gas pressure. |
|
|
Flame failure response time for systems under 400,000 BTUs |
Between 60 and 90 seconds |
|
|
For ignition control module. What could create a false flame condition? |
Short to ground |
|
|
For a flame sensor. How much should be immersed in the burner flame? |
About 1” |
|
|
How does intermittent pilot system differ from DSI and HSI? |
Spark ignited pilot is used to ignite flame upon each burner start up |
|
|
How does intermittent pilot system differ from DSI and HSI? |
Spark ignited pilot is used to ignite flame upon each burner start up |
|
|
What is flame failure response time for intermittent pilot system? |
0.8 seconds |
|
|
How to retrofit a conventional furnace. |
Automatic vent damper and automatic ignition system. This makes it a mid efficient furnace. |
|
|
seasonal Efficiency of conventional furnace and water heater? |
1. 45-58% 2. 30-45% |
|
|
Seasonal efficiency of mid efficient furnace. |
65-75% |
|
|
Seasonal efficiency of non condensing high efficiency furnace. |
75-85% |
|
|
Why does high-efficiency condensing furnace have multiple heat exchangers? |
First heat exchanger is for sensible heat. Second heat exchanger is for latent heat, when air changes to a liquid. |
|
|
Because condensate from the flue gases is slightly acidic, What is the second stage heat exchanger made of. |
Stainless steel |
|
|
With high efficiency condensing furnaces. What can happen if vent length is exceeded? |
Erratic operation and shutdown due to pressure switch tripping out. |
|
|
When 636 passes through an unheated space it must be? |
Insulated |
|
|
636 vent termination must be 4 ft from? 2 things |
Building soffit, inside corner from 2 exterior walls. |
|
|
636 vent termination must be 4 ft from? 2 things |
Building soffit, inside corner from 2 exterior walls. |
|
|
How far must 636 vent termination be from a mechanical air supply inlet to a building? |
6 ft |
|
|
What side of building should vent termination be? |
One that isn’t prone to prevailing winds. |
|
|
How far should 636 vent termination be from building opening or supply inlet of another appliance? 2 |
1. 12” for furnaces 100 000 btuh or less 2. 36” for over that |
|
|
How far must a 636 vent termination be from a gas meter or service regulator? A regulator vent? |
1. Not directly above a gas meter or service regulator 2. At least 6 ft from a regulator vent |
|
|
Spillage in a venting system is a result of what two things? |
Venting system overloaded or appliance is overloaded |
|
|
What 4 things can cause a venting system to be overloaded? |
The appliance is overfiring, appliance venting system restricted or blocked, Venting system to small, venting system poorly designed |
|
|
What two things can cause a Downdraft in a venting system? |
Lack of make up air or chimney or vet location |
