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No local verbatim NFPA 54 text (the inspectapedia file is the front matter only). 248 CMR 5.09 was read in full and amends 9.1.1, 9.1.1.1, 9.1.1.3, 9.1.1.4, 9.1.19.1, 9.1.22, 9.1.23, 9.2.1, 9.6.1.4, 9.6.3.5 and 9.6.8, not 9.6.7. Rule as tested in the bank (q17): a sediment trap is required ahead of the appliance, as close to the inlet as practical, unless it is incorporated in the appliance; illuminating appliances, ranges, clothes dryers, decorative vented appliances, gas fireplaces and outdoor grills are exempt.
Gas piping can carry pipe scale, cutting chips, thread-sealant bits, dirt and sometimes moisture. At the tee, the gas turns 90 degrees while heavier particles keep going straight down into the capped leg, because of their momentum and gravity.
That keeps grit out of gas valve seats, regulators and burner orifices, where it can cause leaks or poor combustion. The older idea behind 'drips' comes from manufactured coal gas, which carried a lot of moisture that condensed and ran to low points in the piping.
Drip pots at low points collected condensed moisture from manufactured gas (as described in a 1981 patent).
Source: https://patents.google.com/patent/US4252152A/en
The National Fuel Gas Code still treats the two together under one section heading.
Source: https://inspectapedia.com/Design/National-Fuel-Gas-Code-NFPA_54-2012.pdf
Mnemonic: 'Gas turns the corner; dirt goes straight down.' The trap only works if the gas has to change direction at the tee. A plain elbow with a nipple hanging off it does not.
Any capped nipple on the gas line is a drip leg.
Without the change of direction at a tee, debris is not separated.
Natural gas is clean, so sediment traps are obsolete.
Construction debris and scale still get into piping. Codes still require them at most appliances.
Under NFPA 54-2012 as adopted in Massachusetts, which appliance is NOT required to have a sediment trap at its inlet?
NFPA 54 requires a sediment trap ahead of an appliance, as close to its inlet as practical, unless one is built into the appliance. It exempts illuminating appliances, ranges, clothes dryers, decorative vented appliances, gas fireplaces and outdoor grills. Furnaces, boilers and water heaters are not exempt, because debris could foul their controls.
The purpose of a sediment trap (drip leg) at an appliance is to:
At the tee the gas turns, but heavier moisture, scale and pipe dope keep going straight down into the capped nipple by momentum and gravity. That keeps debris out of the gas valve and burner orifices, where it could make the valve stick or burners misfire; the drip leg has no effect on pressure.
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