1 HVACR115 – Mechanical for Gas Gas Orifices. 2 Function of the Orifice The burner orifice holds the burner gas input rates to a set level. It meters

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HVACR115 – Mechanical for Gas

HVACR115 – Mechanical for Gas

Gas OrificesGas Orifices

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Function of the OrificeFunction of the Orifice

• The burner orifice holds the burner gas input rates to a set level.

• It meters the gas flow.

• The burner orifice holds the burner gas input rates to a set level.

• It meters the gas flow.

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Designs of the OrificeDesigns of the Orifice

• Inside the spud various angles of approach to the orifice are used.

• The ratio of the orifice diameter to its depth also differs.

• Inside the spud various angles of approach to the orifice are used.

• The ratio of the orifice diameter to its depth also differs.

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Types of OrificesTypes of Orifices

• There are three types of orifices:– Fixed– Adjustable– Universal

• There are three types of orifices:– Fixed– Adjustable– Universal

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Fixed OrificesFixed Orifices

• These are the most common types of orifices.• They consist of a small drilled opening in an orifice

spud.• These are sometimes formed by laser piercing in

materials which are difficult to drill.

• These are the most common types of orifices.• They consist of a small drilled opening in an orifice

spud.• These are sometimes formed by laser piercing in

materials which are difficult to drill.

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Adjustable OrificesAdjustable Orifices

• Used mainly in gas ranges/stoves.• These orifices consist of two parts.

– One moves– The other is stationary.

• Used mainly in gas ranges/stoves.• These orifices consist of two parts.

– One moves– The other is stationary.

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• Movable orifice hood:– A needle inside the orifice spud is stationary.– The orifice in a spud, or hood, moves with respect

to the needle.– By moving the orifice hood closer or farther away

from the tapered needle point the area of opening is changed to adjust the gas flow.

• Movable orifice hood:– A needle inside the orifice spud is stationary.– The orifice in a spud, or hood, moves with respect

to the needle.– By moving the orifice hood closer or farther away

from the tapered needle point the area of opening is changed to adjust the gas flow.

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• Fixed spud– The orifice spud is stationary.– A movable needle is screwed into or out of the

orifice opening to adjust the opening size in either type of orifice.

– Gas rate can be adjusted from zero (with the needle tight against the the orifice wall). To some full rate. The full rate is set by the size of the orifice with no needle in it.

• Fixed spud– The orifice spud is stationary.– A movable needle is screwed into or out of the

orifice opening to adjust the opening size in either type of orifice.

– Gas rate can be adjusted from zero (with the needle tight against the the orifice wall). To some full rate. The full rate is set by the size of the orifice with no needle in it.

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Universal OrificeUniversal Orifice

• Universal orifices are designed to operate with either natural gas or LPG.

• They are also mainly used in ranges.• The universal orifice is a combination of a fixed

orifice and an adjustable orifice.• The needle is in a fixed position.• The orifice hood is free to move.

• Universal orifices are designed to operate with either natural gas or LPG.

• They are also mainly used in ranges.• The universal orifice is a combination of a fixed

orifice and an adjustable orifice.• The needle is in a fixed position.• The orifice hood is free to move.

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• The needle has an orifice drilled through it, sized for LP operation.

• To operate the range with LP gas:– The orifice hood is screwed down until the tapered

needlepoint completely blocks off the orifice in the hood.– LP gas rate is set by the size of the fixed orifice through

the needle.

• The needle has an orifice drilled through it, sized for LP operation.

• To operate the range with LP gas:– The orifice hood is screwed down until the tapered

needlepoint completely blocks off the orifice in the hood.– LP gas rate is set by the size of the fixed orifice through

the needle.

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– To adjust LP rate, the size of the orifice through the needle is changed. This is done by either drilling out the pin orifice or replacing the needle with a smaller one.

• For natural gas operation the orifice hood is screwed away from the needle.– Gas will flow through both the fixed orifice in the

needle and through the opening between the needle and the edge of the orifice.

– To adjust LP rate, the size of the orifice through the needle is changed. This is done by either drilling out the pin orifice or replacing the needle with a smaller one.

• For natural gas operation the orifice hood is screwed away from the needle.– Gas will flow through both the fixed orifice in the

needle and through the opening between the needle and the edge of the orifice.

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Orifice DischargeOrifice Discharge

• Gas flow rate through the orifice depends on three things:– Orifice Size– Gas Pressure forcing the gas through the orifice– Specific gravity of the gas.

• Change any one of these and the gas flow changes.

• Gas flow rate through the orifice depends on three things:– Orifice Size– Gas Pressure forcing the gas through the orifice– Specific gravity of the gas.

• Change any one of these and the gas flow changes.

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Orifice DischargeOrifice Discharge

• Remember, less gas always flows through the orifice than the theoretical amount.

• Remember, less gas always flows through the orifice than the theoretical amount.

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Measuring Gas Flow RatesMeasuring Gas Flow Rates

• Gas input rates of appliances are checked by metering the gas flow.

• To obtain an accurate check of the rate for one gas appliance all other gas appliances and the pilots must be turned off during the check.– Hint: leave truck keys on top of any appliance you

are turning off so you remember to turn it back on.

• Gas input rates of appliances are checked by metering the gas flow.

• To obtain an accurate check of the rate for one gas appliance all other gas appliances and the pilots must be turned off during the check.– Hint: leave truck keys on top of any appliance you

are turning off so you remember to turn it back on.

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Measuring Gas FlowMeasuring Gas Flow

• For most orifice spud designs, orifice sizes taken from the charts should give input rates very close to the desired rate.– If an orifice must be replaced with a flat bottomed one.– The rate obtained may be low for the orifice size

selected.

• For most orifice spud designs, orifice sizes taken from the charts should give input rates very close to the desired rate.– If an orifice must be replaced with a flat bottomed one.– The rate obtained may be low for the orifice size

selected.

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• If the rate is not close enough to the desired rate, it may be altered by adjusting gas pressure slightly.

• If the rate is not close enough to the desired rate, it may be altered by adjusting gas pressure slightly.

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• Steps:– Turn on ONLY the appliance you are interested in and

go to the gas meter.– Use a watch with seconds and count the number of

seconds it takes for the dial to revolve one time.– Look at the meter and find out how many cubic feet is

used in this one revolution.

• Steps:– Turn on ONLY the appliance you are interested in and

go to the gas meter.– Use a watch with seconds and count the number of

seconds it takes for the dial to revolve one time.– Look at the meter and find out how many cubic feet is

used in this one revolution.

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• Use the following formula:– Cubic Feet per Hour =

• (cubic feet per revolution) X 3600• --------------------------------------------• Time of revolution in seconds

– The number 3600 converts seconds to hours.

• Use the following formula:– Cubic Feet per Hour =

• (cubic feet per revolution) X 3600• --------------------------------------------• Time of revolution in seconds

– The number 3600 converts seconds to hours.

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• For example a meter using 1/2 cubic foot of gas per revolution takes 15 seconds to revolve one time with the furnace running.– CFH=(.5 x 3600) / 15 = 120cfh

• For example a meter using 1/2 cubic foot of gas per revolution takes 15 seconds to revolve one time with the furnace running.– CFH=(.5 x 3600) / 15 = 120cfh

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• An Example:– A meter uses 2 cubic feet per revolution of the dial, the

time of revolution is 60 seconds with the furnace running.

• CFH = (2.0 x 3600) / 60 = 120cfh

• An Example:– A meter uses 2 cubic feet per revolution of the dial, the

time of revolution is 60 seconds with the furnace running.

• CFH = (2.0 x 3600) / 60 = 120cfh

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Heat input rateHeat input rate

• The heat input rate would be found by measuring the gas flow and then multiplying be the BTU value of the gas.

• There are tables that have been created to help calculate this gas flow rates.

• The heat input rate would be found by measuring the gas flow and then multiplying be the BTU value of the gas.

• There are tables that have been created to help calculate this gas flow rates.

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Documents

1 HVACR115 – Mechanical for Gas Gas Orifices. 2 Function of the Orifice The burner orifice holds the burner gas input rates to a set level. It meters