4.2.21 Student Book © 2004 Propane Education & Research CouncilPage 1 4.2.21 Purging Vapor Distribution Lines & Appliances Purging is the controlled displacement

4.2.21 Student Book © 2004 Propane Education & Research Council Page 1

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


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.


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.


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.



• 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.

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.



• 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

A general outline of activities during a purging operation would include the following:



• 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 Pages 3 & 4

Identifying Procedures for Purging Lines Indoors

Figure 1. Purging Burner Kit Figure 2. Electric/LP-Gas IgnitersStraight (Top),

“Goose Neck” (Bottom)

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 3. Combustible Gas Indicator (CGI)

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.

4.2.21 Student Book © 2004 Propane Education & Research Council Pages 4 & 5


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 PowerDisconnect in Off” Position



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.



E le c t r i c / L P - G a sIg n i t e r

B u n s e nB u r n e r

T e s t T a pS h u t o f f

Figure 5. Purging Using a Controlled Burner and Constant Ignition Source



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.



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).



Step 7: While controlling the venting of gas through the pressure tap, remove the burner fitting or purging valve, and 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 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.



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.



Figure 6. Purging Using a Continuously Sampling Combustible Gas Indicator

C o m b u s t i b l e G a sI n d i c a t o r ( C G I )

Te s t Ta pS h u t o f f



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.



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.



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.


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



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.

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 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.



Figure 7. Packaged HVAC Unit and Power Disconnect

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: 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.



Figure 8. Purging Point on Outside Unit Heating/Air Conditioning Unit

(If the Shutoff Does Not Have a Pressure Test Tap)



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.


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 Pages 12 - 15

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.

Documents

4.2.21 Student Book © 2004 Propane Education & Research CouncilPage 1 4.2.21 Purging Vapor Distribution Lines & Appliances Purging is the controlled displacement