Gas line sizing Flashcards
NPS stands for?
(Nominal pipe size) As the pipe gets stronger the wall thickness increases and the inner diameter decreases
Consideration when sizing a gas line?
- Type of fuel
- Length of piping (longest run)
- Individual branch loads
- Maximum flow capacity
- Type of materials to deliver the gas
- Within allowable maximum pressure drop
Where is the gas load for the appliance determined from?
Gas load for the appliance will be determined from the rating plate
Maximum pressure drop Natural gas?
1 inch WC
Maximum pressure drop Propane?
1 inch WC
If pressure drop exceeds the maximum?
The gas line is probably undersized and a larger line may need to be installed
What type of gas piping materials can be used?
Steel
Cooper
Polyethylene (plastic)
What schedule of black iron pipe is most commonly used for gas connections?
Pipe-schedule 40 steel.
For residential it is threaded and rated for a maximum of 125 psi
What is the minimum diameter for threaded pipe used for natural gas, unless it is schedule 80?
Threaded pipe for natural gas must not be smaller than 1/2 inch diameter unless it is schedule 80
When can pipe used for propane be smaller than 3/8 inch?
Pipe used on propane may be smaller then 3/8 inch if it is used for a branch line to a single appliance no longer than 25 feet.
What type of fittings are to be used with steel pipe?
Steel or malleable iron fittings are to be used with steel pipe
What is the maximum size of steel pipe that can be threaded in a gas piping system?
Maximum size steel pipe that can be threaded in a gas piping system is 2”
What materials can tubing be made of?
Tubing can be cooper or steel
How can copper be joined, and what must it be pressure rated for?
Cooper can be joined by flaring, brazing or compression fittings and must be pressure rated for 125 psi
Types of cooper:
Type K used for?
Underground gas, oil and water lines as well as plumbing and HVAC above ground, very thick wall
Types of cooper:
Type L used for?
Plumbing and heating systems, medium wall thickness
Types of cooper:
Type M used for?
Water distribution systems, heating and sprinkler system, thin wall
Types of cooper:
Type G used for?
All above ground and indoor natural gas and propane installations
Plastic pipes used for?
Outdoors, underground. Is joined using thermal fusion or compression. Tracer wire required. Does’t work with liquid propane.
Hose minimum rated working pressure for hose and hose fittings?
350 psi
Maximum length of hose on a permanent installation?
10’
Minimum length of hose on a construction heater?
15’
Maximum length of hose on a portable appliance (BBQ)?
30’
How must CSST be protected if run inside a wall?
CSST (corrugated stainless steel tubing) if run inside a wall must be protected from damage using protection plates
How are bushings allowed to be used?
Bushings are allowed but they cannot be nested
How can appliances such as a gas range or dryer be connected?
Appliances such a gas range or dryer can be connected with flex connector
What is the maximum length of a flex connector on a vented appliance?
2’
What is the maximum length of a flex connector on an unvented appliance?
6’
What length of unthreaded pipe must be exposed when a pipe protrudes through a ceiling or wall?
1”
What length of unthreaded pipe must be exposed when a pipe comes through a floor?
2”
What is the minimum depth (length) of a drip/dirt pocket, and how is it determined?
Drip/dirt pocket is designed to collect water, liquids, dirt, debris and the depth (length) of the pocket must be minimum 3” or the diameter of the piping it serves whichever is greater
Which 3 fittings cannot be used in a gas piping system?
- Street tees
- Street elbows
- Close nipples
What is the minimum depth at which gas lines must be buried, and how does this change for commercial installations when gas lines traverse a driveway or parking lot?
15” and 24”
What color must gas lines be painted in commercial buildings?
Yellow
Where must yellow band markings be placed for gas or propane lines?
Yellow band markings at 20’ gas or propane markings at 20’
Where must yellow bands be placed on residential copper tubing?
Residential cooper tubing must have yellow bands at 6’
Where should the shut-off be installed in relation to the appliance, and how far can it be from the appliance?
Shut off will be installed on the final drop or rise and close as possible to the valve train of the appliance usually within 2’. It can be located up to 50’ away from the appliance as long as it is accessible and clearly tagged.
If gas line on the roff, what is the maximum length of pipe before an expansion loop is required?
100’
What is the pressure and duration for rough-in testing?
15 psig for 15 min
What is the duration and pressure for finish testing?
10 minutes at working pressure
What is the allowable pressure drop when pressure testing a gas line?
0” wc
What is the minimum size of the face on a test gauge?
3” in diameter
Visibility
Accuracy
Durability
After the pressure test where should the air be vented to, and how far should the purge point be from a building or air intake?
The air should be vented to a safe location and the purge point should not be any closer than 10’ to a building or air intake.
What type of inert gas should be used when purging a gas line that is 4” or larger?
Carbon Dioxide or Nitrogen
What is standing pressure, and what are the typical settings for natural gas and propane?
Standing pressure is the pressure in a gas line that taken downstream of the service regulator and/or the second stage regulator and upstream of the appliance regulator with only the pilot burning.
It is usually set at 7” wc for natural gas and 11” wc for propane.
What is operating pressure, and where is it measured in the gas line?
Operating pressure is the pressure in the gas line taken downstream of the service regulator and upstream of the appliance regulator with the appliance’s main burner operating.
What is differential pressure, and what is the maximum allowable pressure drop?
Differential pressure (also called pressure drop or pressure loss) is the difference between the standing pressure and operating pressure.
The maximum pressure drop is 1” wc
What is manifold pressure, and where is it measured?
Manifold pressure is the pressure at the burner. It is taken downstream of the appliance regulator with the main burner operating.
How can inches of water column be converted to psi?
nches of water column can be converted to psi by multi plying by 0.0361.
1 psi in “wc?
28” wc
14”wc in psi?
0.5 psi
When is it necessary to add equivalent length for fittings in a 2 psi gas line installation?
In a 2 psi gas line installation, you will need to add equivalent length for fittings if you have more than a reasonable amount.
How far must a vent termination be from a moisture exhaust duct?
Vent termination must be at least 3’ from a moisture exhaust duct
What is the maximum pressure drop allowed in 2 psig systems, and where can it be found?
2 psig systems allow up to a 75% pressure drop depending on the sizing table. Table A.4 with a pressure drop of 1.5 psig
