Module 9 Gas Appliances

List the components of a typical natural draft venting system

Vent pipe

Supports

Fire stop spacers

Roof Flashing

Storm collar

Vent Cap

What are the four functions of a venting system

Removes the flue products to the outdoors

Prevents damage from condensation

Protects the building from fire hazard

Provides air circulation

Name two products produced by complete combustion of natural gas or propane

Carbon Dioxide

Water Vapour

What are the conditions that provide a natural draft venting system with the greatest amount of draft

High stack temperature

Low outdoor temperature

High stack height

What type of venting system relies on the upward movement of hot gases

Natural draft vent

What device allows dilution air to enter the venting system of an atmospherically fired appliance

Draft hoods

Which type of vent is required when flue gas temperatures exceed 470F

Chimney Type A

Which type of vent has a double-wall construction with a dead air space between the walls

Type B Vent

Type BW vent

Type L vent

Which type of vent draws in combustion air emits flue gases from the same vent

Direct Vent

List four common venting problems

Excessive laterals

Blockage

Excessive change of direction

Incorrect or missing vent caps

Describe the function of the following type B vent components

Supports vent stack

Maintains clearance from combustion material

Fire stop spacer

Block stack effect during a fire and maintains clearances from combustible material

Roof flashing/storm collar

Prevents moisture from entering home

Vent cap

Prevents moisture or foreign object from entering vent system

How does increasing vent temperature or height affect the draft of a natural draft venting system

It increases the draft

Term for steel or masonry chimney

Type A

Term for double wall vent with aluminum inside

Type B

Term for double wall vent with stainless steel inside

Type L

Term for double wall(oval) with aluminum inside

Type BW

Term for single thickness of galvanized or aluminum

Single wall or Type C

Term for venting system under positive pressure

Type BH

To what ULC standard must all plastic material used in type BH venting system be approved

U.L.C standard S636

Can a chimney with a clay tile liner be lined with a metallic liner system

Yes Some types of applications and situation requires a liner to be installed to prevent condensation

Direct vent appliance

(a) Where does it take it's air from

Outside

How is this accomplished

The unit is sealed and a seperate pipe is used for the exhaust and the intake and there are no openings to the interior of the building

State three situations where they are used

When a hazardous atmosphere exists in a building

When a building may experience negative pressure

When it is not favorable to use a natural draft Vent

List styles of draft hoods

Vertical

Horizontal

Describe the functions of a draft hood with respect to Temperature and humidity of the flue products

Dilutes the flue products to reduce the temperature and humidity

Describe the functions of a draft hood with respect to Stack effect on the combustion chamber

Negates the effect of the chimney draft to stabilize the combustion process

Describe the functions of a draft hood with respect to Handling of down draft

Diverts the down-draft away from the combustion chamber to reduce the chances of (Co) production during a down draft condition

Explain the operation of the following barometric dampers Double Acting

Swings into regulate the stack draft and also swing s out to relieve a down daft into the room

Explain the operation of the following barometric dampers Single Acting

Only swing into regulate the stack draft and closes shut when a double draft is present to prevent soot or ashes from entering

When is a single acting barometric damper allowed on a propane or natural draft appliance

For an incinerator only

What determines the adjustment of a barometric damper

-The type of burner

-Combustion chamber

- Manufacturer's literature

Describe the effect on an appliance with a barometric damper if, The stack draft is increased

-It will raise

- Neutral pressure pointed

-Lowers the efficiency

Describe the effect on an appliance with a barometric damper if, The stack is decreased

Will lower the neutral pressure point

Increase the efficiency to a point (Co) can be produce

How many screws are required at each joint of single wall material

Three

Why do designed boiler and water heater manufacturers stamp the distance from the draft hood skirt to the top of the boiler on the draft hood and why is this extremely important

-Prevents Shortening of Flue pipe to accommodate the installed.

-The burner neutral pressure point will lower

-Excess air will lower to the point of producing carbon Monoxide

Describe the undesirable effects of a vent connector coming loose and falling off a gas appliance

Flue products could have (Co)

Recirculation of Flue products could cause (Co)

Resulting personal injury or death to the building occupants

How will the following appliances react to a block vent

Will spill flue products into the room

Appliance with a fan assisted combustion system

A shut off switch will activate to shut down the burner

Natural draft appliance equipped with a spill switch

The spill switch will shut the appliance down and require resetting

Air is drawn in by the vacuum created by the injection of gas to the burner

Inspirator

Air moving through the burner creates a negative pressure that draws the gas into the burner to be mixed

Aspirator

Gas is drawn in by the negative pressure created by a blower that is also drawing in air for combustion

Blower Mix

A regulator designed to supply gas at or atmospheric pressure when a vacuum is induced on it

Zero Govenor

Air drawn into burner by Venting action

Atmospheric Burner

Air is supplied to burner under enough pressure to overcome resistance of burner only

Fan Assist Burner

Air is supplied to burner under enough pressure to overcome the resistance of the burner and the appliance

Force Draft Power burner

Air and gas are mixed completely before introduction to the chamber by inspiration aspiration or blower mix methods

Pre-mix Burner

Which atmospheric burners are the most susceptible to flashback

Mono Port

What helps to keep the flame retained at the burner port of a mono port burner

Crimped ring

What is multi port burner susceptible to

Clogging with lint from the inside

What term is used to describe a burner flame that moves back through the burner nozzle

Flashback

Through which device is fuel discharged to an atmospheric burner

Orifice

Which type of atmospheric burner produces a single large flame

Single or mono port burner

List four common types of multi port atmospheric burners

Drilled Port

Drilled Pipe

Slotted Port

Ribbon Port

What are the recommended minimum and maximum port diameters for drilled port atmospheric burners

Maximum No 29 Drill

Minimum No 42 Drill

Which type of burner has combustion air supplied by a fan or blower under sufficient pressure to overcome the restriction of the burner and the appliance

Force Draft Burner

Which type of burner has a fan located downstream of the combustion zone

Induced Draft burner

What provides the kinetic energy to entrain the gas required for a premixing inspritor burner

The gas coming out of the orifice into a gas jet mixer

What device is used to regulate gas supply to an aspirator type burner

Zero Governor

Which type of burner provides complete premixing using mechanical mixers

Blow Mix

How do you correct Lifting flame with an atmospheric burner

Reduce primary Air

Reduce appliance input rate

Only if higher than specified on the appliance rating plate

How do you correct Yellow tipping with an atmospheric burner

Clean burners thoroughly

Adjust primary air opening

How do you correct Flame roll-out(Steady) with an atmospheric burner

Heat exchanger blocked or cracked on a forced air furnace

if not check appliance input rate

How do you correct Flame roll-out (Upon ignition)with an atmospheric burner

Check for correct manifold pressure settings and that the proper types of gas controls are used for the appliance

What are the two basic types of pilot burners?

-Aerated Pilots

-Non aerating pilots

What is the most common problem associated with aerated pilots

Clogging due to dust or lint

When you discover a noisy, lifting, blowing flame on a non-aerating pilot,what is the cause of the problem and remedy?

Cause high gas pressure

Reduce gas pressure

Explain the term proved pilot

A pilot flame supervised by a flame safeguard control

-Detects the pressure of a flame before allowing the main fuel valves to open

How is a piezoelectric voltage generated

Through a mechanical force

How has the use of modern automatic ignition systems affected the time in which a flame failure is detected

Flame failure is detected much faster

What causes the bi-metal strip to curve with changes in temperature?

The two metals that are joined have different temperature coefficients of expasion

What causes the resistance of a thermistor to change

A temperature change

Describe a constant pilot?

Remains on all the time

Describe a Intermittent pilot

Remains on during the firing cycle

Describe a Interrupted pilot

-Turns on to light the main flame

-Extinguished after the flame has been proved

Describe a Standing Pilot

Pilot remains on all the time regardless of whether sensed or not.

Describe 100% Safety

Pilot and Main Burners are shut off if flame is not sensed

Describe a spark ignited pilot

Pilot is lit, or re-lit by a spark

Describe a Hot surface ignition

Pilot or main burner is ignited by hot surface device(Glow Bar)

Flame sensing method: Constant Supervision

Supervises the flame and must be in constant attendance

Flame sensing method: Bi-metal

Two different metals are bonded

Warps in change to temperature

Warping activates a switch to gas valve

Flame sensing method: Bulb and Bellows

-A Bulb filled with fluid senses medium temperature

-Bellows that will expand or contract when temperature changes

-Expanding Bellows activates a switch to control gas flow to Burner

Flame sensing method: Thermistor

-Electrical resistance changes in response to temperature

-Control responds to resistance which operates a switch to control gas flow to burner

Flame sensing method: Thermocouple

Hot junction is heated by the pilot flame

Voltage is generated closing a pilot valve/Switch

Flame sensing method: Optical sensors

Allows gas to conduct electricity

What is the purpose of an operating aqua-stat

Energize or D-energize the main gas valve in response to the water temperature (180F)

Is the temperature setting of a high-limit aqua-stat higher or lower than the setting of the operating aqua-stat?

Higher

Does the furnace fan continue to run if the high-limit switch opens the furnace control circuit?

Yes

What causes the contacts of a steam boiler operating pressure control to open

A rise in steam pressure

Name two types of low water cut-off switches used on gas-fired boilers

-Probe Type

-Float Type

What activates a flame roll-out switch

A raise in temperature

Senses the operation of a circulating pump

Flow Switch!

A water temperature sensing device that will shut off the burner if the temperature exceeds the desired operating range of the boiler or water heater

High Limit Aqua-Stat!

Shuts off the burner in the event that the pressure in a boiler exceed it's desired operating range

High Limit Pressure Switch!

Turns a steam boiler on and off to maintain a desired steam pressure

Operating Pressure Switch!

Turns a boiler or water heater on and off to maintain a desired water temperature

Operating Aqua-Stat!

Shuts the burner off if the water level in a system falls below a desired point

Lower-Water Cut Off Switch!