4.2.21
Purging Vapor Distribution Lines
& Appliances
Purging is the controlled displacement of air or inert gas
from distribution lines, and is a requirement of NFPA 54,
National Fuel Gas Code, prior to placing propane appliances
into service.
In this module you will learn to identify:
(1) NFPA 54 requirements for purging gas distribution lines and
appliances
(2) reasons for purging gas distribution lines and appliances
before placing the appliances into service
(3) Procedures for purging lines indoors
(4) Procedures for purging lines outdoors
(5) Procedures to perform when all line purging is completed
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page 1
NFPA 54 Requirements for Purging Gas Lines & Appliances
NFPA 54
2002
7.3.2 Placing in Operation. When piping full of air is placed in
operation, the air in the piping shall be displaced with fuel gas,
except where such piping is required by Table 7.3.2 to be
purged with an inert gas prior to introduction of fuel gas. The
air can be safely displaced with fuel gas provided that a
moderately rapid and continuous flow of fuel gas is introduced
at one end of the line and air is vented out at the other end.
The fuel gas flow shall be continued without interruption until
the vented gas is free of air. The point of discharge shall not be
left unattended during purging. After purging, the vent shall
then be closed. Where required by Table 7.3.2, the air in the
piping shall first be displaced with an inert gas, and the inert
gas shall then be displaced with fuel gas.
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page 1
NFPA 54 Requirements for Purging Gas Lines & Appliances
NFPA 54
2002
7.3.3 Discharge of Purged Gases. The open end of piping
systems being purged shall not discharge into confined spaces
or areas where there are sources of ignition unless precautions
are taken to perform this operation in a safe manner by
ventilation of the space, control of purging rate, and elimination
of all hazardous conditions.
7.3.4 Placing Equipment in Operation. After the piping has
been placed in operation, all equipment shall be purged and
then placed in operation, as necessary.
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page 1
Reasons for Purging Gas Distribution Lines and Appliances
•
Only qualified gas service personnel should do purging operations.
•
There are particular difficulties with purging furnaces and boilers equipped with
electronic ignition systems. These appliances are designed to provide a limited
number of programmed ignition trials before they go into a shutdown mode,
requiring a system control reset before additional ignition trials will occur. This
safety feature of electronic ignition systems requires that the distribution lines
supplying the appliance be purged of air (or inert gas).
•
Since propane must be used to purge and fill the distribution lines, a potential
hazard exists. Improper purging may cause propane vapor and combustible
gas-air mixtures to escape to the atmosphere in the building, and could cause
an explosion or fire if an ignition source is present. Therefore, it is extremely
important that a specific procedure be followed to thoroughly remove the air or
inert gas in a way that does not create the hazard of fire or explosion.
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page 2
Reasons for Purging Gas Distribution Lines and Appliances
Warning! Purging propane-air mixtures to the atmosphere unburned is
hazardous! Never loosen a pipe union, flare connection or sediment trap
cap for the purpose of purging gas lines inside a structure or enclosed
area.
•
Line purging using proper procedures is necessary on all new systems, on
changed or modified systems, and whenever systems are shut down for
extended periods of time or by the interruption of gas service.
•
Air or inert gas must be removed from the piping of a propane system before
attempts are made to place the system and its gas appliances into service.
Failure to do so will cause difficulty in lighting pilots and improper operation of
electronic ignition systems. Adjustable appliance burners cannot be properly
adjusted until all the air or inert gas is removed from the lines.
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page 2
Reasons for Purging Gas Distribution Lines and Appliances
A general outline of activities during a purging operation would include the following:
•
Make sure the supply tank or cylinder(s) has been properly purged of air and
filled with propane. It is not possible to properly purge air form the distribution
lines if air is present in it.
•
Purge lines only after the piping system has been pressure tested and
determined to be leak-free.
•
Purge the buried distribution line (connecting the regulator at the supply
container to the building service entrance equipped with an outside shutoff
valve, or second-stage or 2-PSI service regulator) outdoors. Appliances
installed outdoors should be purged outdoors.
•
Integral two-stage regulator controlled and single-stage regulator controlled
lines (where existing single-stage regulators are permitted) should be purged
using a controlled ignition burner or combustible gas indicator (CGI) to prevent
accumulation of combustible gas-air mixtures
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page 3
Reasons for Purging Gas Distribution Lines and Appliances
•
Before actual purging, know the requirements of the piping system layout
including:
1.
Separate service entrances
2.
Trunk and branch lines
3.
Distribution manifolds and branch lines
4.
Unusually long or large diameter lines
5.
During purging, close all valves, if you must leave the purging location for
any reason and for any length of time.
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page 3
Identifying Procedures for Purging Lines Indoors
Equipment Used When Purging Lines Indoors When purging operations are
conducted indoors, controlling the purging rate and eliminating hazardous conditions
can be accomplished by using a controllable auxiliary combustion burner and
continuous igniter or combustible gas indicator (CGI).
Purging Burner Kit
Figure 1. Purging Burner Kit
Figure 2. Electric/LP-Gas Igniters
Straight (Top),
“Goose Neck” (Bottom)
4.2.21 Student Book  © 2004 Propane Education & Research Council
Pages 3 & 4
Identifying Procedures for Purging Lines Indoors
Combustible Gas Indicator A combustible gas indicator monitors the purged
gas to determine when it’s approaching a combustible level. The CGI/CO (carbon
monoxide) unit shown in Figure 3 uses an internal sampling pump to continuously
monitor the environment at the purging point, and gives an audible alarm and display
reading when the purging atmosphere reaches the lower explosive limit (LEL) for
propane. The CGI purging method can be used indoors or outdoors.
Figure 3. Combustible Gas
Indicator (CGI)
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page
4
Identifying Procedures for Purging Lines Indoors
Procedures Typically Used for Purging Lines Before starting, follow these
precautions:
•
Verify that appliance shutoffs are in the closed or off positions, and that all
distribution lines that are not connected to appliance shutoffs are capped or
plugged.
•
Verify that the thermostats that control gas appliances are in the “off” position,
and power disconnects to outdoor packaged heating and air conditioning units
are also in the “off” position. (Figure 4)
Figure 4a. Thermostat in
“Off” Position
Figure 4b. HVAC Unit Heater Power
Disconnect in Off” Position
4.2.21 Student Book  © 2004 Propane Education & Research Council
Pages
4&5
Identifying Procedures for Purging Lines Indoors
Procedures Typically Used for Purging Lines Before starting, follow these
precautions:
•
A survey of the area surrounding purging points for other uncontrolled sources
of ignition must be done. If any are found, they must be eliminated or
controlled.
•
Purging points and the order of line purging should be planned out to minimize
the possibility of trapping pockets of air or inert gas that would hamper purging
appliances and placing them into service.
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page
5
Identifying Procedures for Purging Lines Indoors
Test Tap
Shutoff
Electric/LP-Gas
Igniter
Figure 5. Purging Using a Controlled Burner
and Constant Ignition Source
4.2.21 Student Book  © 2004 Propane Education & Research Council
Bunsen
Page
6
Identifying Procedures for Purging Lines Indoors
Step 1:
Make sure the shutoff ahead of the appliance is closed.
Step 2:
In 2-pound vapor distribution systems, be sure that the
purging point and connection to the purging burner is
downstream of a line regulator so that the burner will receive
purge gas at pressures reduced from 2 psig to required
burner input pressure.
Step 3:
Ensure that the burner valve and (if used) the purging valve
is closed. Remove the test tap plug from the shutoff and
immediately install the purging valve or burner connection as
applicable. If the pressure test tap is upstream of the
appliance shutoff, apply measures to control the venting of
gas through the pressure tap during the installation of the
purging valve and/or burner connections.
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page
6
Identifying Procedures for Purging Lines Indoors
Step 4:
With the purging burner valve closed, open the
appliance shutoff and check the connections for
leakage.
Step 5:
Ready the electric/LP-gas igniter, then open the purging
burner valve. Ensure that the igniter applies a
continuous flame within a suitable distance immediately
above the burner ports or flame retention wire mesh
screen (if a Bunsen burner is used).
Step 6:
When a steady propane flame is ignited and can be
maintained without the presence of the electric/LP-gas
igniter present, close the appliance shutoff, and
immediately after the flame extinguishes—close the
purging burner valve and purging valve (if used).
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page
6
Identifying Procedures for Purging Lines Indoors
Step 7: While controlling the venting of gas through the pressure tap,
remove the burner fitting or purging valve, and immediately reinstall the test tap plug and covering cap, if so equipped.
Open the appliance shutoff and check the test tap for leakage
using a suitable leak detection solution. Be sure to apply leak
detection solution only to the immediate area of the test tap,
and avoid soaking the valve stem of any shutoff or appliance
gas cock.
Complete this series of purging operations for each gas appliance. When purging
gas cook tops and ranges, a top surface burner unit can be used for purging.
Although electronic ignition models provide a relatively reliable ignition source for
purging, it is recommended that the continuously operating electric/LP-gas igniter
used with the purging burner previously discussed is used as a measure to ensure
proper ignition of purged gas.
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page
7
Identifying Procedures for Purging Lines Indoors
WARNING! Do not rely on a match instead of a torch or external
electric/LP-gas igniter during purging of gas ranges, cook tops, or
any other appliance. A single match or series of matches do not burn
long enough to accomplish the job.
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page
7
Identifying Procedures for Purging Lines Indoors
Test Tap
Shutoff
Combusti bl e Gas
IndiFigure
cator
(CGI)
6. Purging
Using a Continuously
Sampling Combustible Gas Indicator
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page
7
Identifying Procedures for Purging Lines Indoors
WARNING! Read and follow CGI manufacturer instructions for
calibrating, verifying proper instrument operation, handling, and
use of the CGI unit in purging operations or any other uses.
Step 1:
Ensure that the CGI is properly calibrated for propane, and that
it properly displays a “zero” reading in clean air before each
purging operation.
Step 2:
Make sure the shutoff valve ahead of the appliance is closed.
In 2-pound vapor distribution systems, be sure that the purging
point is downstream of a line regulator so that the purged gas is
controlled at a uniform discharge pressure and that the volume
of discharge is not excessive.
Step 3:
Ensure that appliance-controlling thermostats are in the “off”
position.
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page
8
Identifying Procedures for Purging Lines Indoors
Step 4:
Ensure that there are no ignition sources nor any combustible
gases or other materials in the immediate area of the purging
operation.
Step 5:
If conditions indicate a need for ventilation, provide ventilation
in a manner than will not interfere with continuous CGI
sampling of the purged gas.
Step 6:
Verify that the CGI is on and set on the LEL alarm setting.
Remove the plug from the pressure test tap of the shutoff and
position the sampling tube immediately below the test tap
opening. NOTE: The flexible sampling line inlet or wand is not
connected to the test tap, rather it is held directly below the test
tap purging point.
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page
8
Identifying Procedures for Purging Lines Indoors
Step 7:
Open the shutoff and begin purging. Continue monitoring the
CGI
Step 8:
Stop purging if propane is detected by smell or CGI alarm.
Immediately close the shutoff.
Step 9:
While applying measures to control the venting of gas through
the pressure tap, immediately re-install the test tap plug and
covering cap, if so equipped. Open the appliance shutoff and
check the test tap for leakage using the CGI on the ppm scale,
or a suitable leak detection solution. Be sure to apply leak
detection solution only to the immediate area of the test tap,
and avoid soaking the valve stem of any shutoff or appliance
gas cock. Avoid exposing the CGI, and especially the sampling
inlet, to leak detector solution.
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page
8
Identifying Procedures for Purging Lines Outdoors
Complete this series of purging operations for each gas appliance. When
purging gas cook tops and ranges, a top surface burner unit can be used
for purging.
Identifying Procedures for Purging Gas Lines Outdoors
Two types of distribution lines are purged outdoors:
1.
Buried distribution lines (first-stage lines) connecting first-stage and
second-stage or 2-PSI service regulators
2.
Distribution lines to appliances located outdoors
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page
9
Identifying Procedures for Purging Lines Outdoors
Steps for Purging First-Stage Lines— Purging outdoors may be done at the
test tap of a shutoff valve installed below the second-stage or 2-PSI service regulator,
or at the test tap on the inlet side of the regulator.
Step 1:
Attach a purging valve assembly, with tubing or hose for remote
discharge, if needed. Make sure the purging valve is closed.
Step 2:
Pressurize the distribution line by slowly opening the container
service valve.
Step 3:
Fully open the purging valve for three (3) seconds.
Immediately close the purging valve after 3 seconds. This
is adequate time for purging up to 100 feet of 5/8-inch OD
copper tubing. Additional purging is not necessary.
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page
9
Identifying Procedures for Purging Lines Outdoors
Step 4:
Close the container service valve. Open the purging valve to
depressurize the line. Remove the purging valve and
immediately replace the plug in the shutoff or regulator test
tap.
Step 5:
Open the container service valve to pressurize the system.
Apply a suitable leak detection solution or use a CGI set to
indicate parts per million (ppm) to make sure there is no
leakage at the test tap plug.
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page
9
Identifying Procedures for Purging Lines Outdoors
Steps for Purging Distribution Lines to
Appliances Located Outdoors. Purging outdoors
may be done at the test tap of a shutoff valve, or a
piping union
Step 1: Ensure that the controlling thermostat
for the appliance and the power
disconnect are in the “off” position,
and that there are no sources of
ignition near the purging area. Verify
that the shutoff is closed.
Step 2:
Figure 7. Packaged HVAC Unit
and Power Disconnect
If a union in connecting piping is used as the purging point, use a
back up wrench to ensure that when the mating nut of the union is
loosened that the coupling ends are not turned. If a test tap in the
appliance shutoff is available, use it as the purging point and not
the union.
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page
10
Identifying Procedures for Purging Lines Outdoors
Figure 8. Purging Point on Outside Unit
Heating/Air Conditioning Unit
(If the Shutoff Does Not Have a Pressure Test Tap)
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page
10
Identifying Procedures for Purging Lines Outdoors
Step 3:
If a CGI is available, use it to continuously monitor purging on
the LEL scale setting. Open the shutoff and briefly purge the
line. Stop purging if propane is detected by smell or CGI alarm.
Immediately close the shutoff.
Step 4:
Replace the test tap plug or retighten the union nut, using a
back up wrench to avoid turning the coupling ends.
Step 5:
Re-open the shutoff and re-pressurize the appliance connective
piping. Use the CGI on the ppm scale or a suitable leak
detecting solution to check for leakage at the test tap or union.
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page
10
Procedures to Perform When All Line Purging is Completed
When all line purging has been completed, complete the following operations
before placing the vapor distribution system and appliances into service:
•
A leak check must be completed as prescribed in Chapter 7 of NFPA 54, 2002
edition. The system leak check must be documented along with a description
of any leaks found and repaired.
•
Appliances are placed into service as directed in appliance manufacturers’
operating and lighting instructions.
•
A flow pressure test and lock-up test is performed on the system pressure
regulator(s).
•
Because the lock-up test must be done with the appliance shutoffs closed,
appliances are placed into service as directed in appliance manufacturers’
operating and lighting instructions for a second time. Burner operation should
be observed through at least two call-for-heat cycles to assure proper burner
operation and that appliance purging is complete. If any appliance burner
does not operate properly, it should be adjusted or repaired as needed by a
qualified gas technician.
4.2.21 Student Book  © 2004 Propane Education & Research Council
Page
11
Time to See If You Got the Key Points of
This Module…
• Complete the Review on pages 12 & 13.
• See if you are ready for the Certification
Exam by checking off the
performance criteria on pages 14 &
15.
4.2.21 Student Book  © 2004 Propane Education & Research Council
Pages 12 - 15