Question by jstlttllm: Questions about my Gas Hot Water Heater?
what are sediment traps and drip legs for a gas hot water heater? What do they do? Can not having them be dangerous?

Best answer:

Answer by Cragar
Drips and sediment traps are two separate and distinct devices. While the terms are often used interchangeably because they are similarly constructed, they have different functions, and care should be taken not to confuse the two. The National Fuel Gas Code Handbook distinguishes the terms like this:

A sediment trap is installed to collect solid foreign particles (debris) and prevent such material from interfering with the operation of controls and safety devices, or clogging of small passageways. This sediment is inadvertently introduced into the system during installation or replacement of piping, fittings, and controls. Since the accumulation of sediment is not expected to be continuous, these traps do not require routine servicing.

A drip trap (sometimes called a drip leg) is installed at a low point in the system of gas piping to collect condensation, allowing for its removal. These traps are for wet gas. As noted in the National Fuel Gas Code, “Many old manufactured gas installations used low-pressure mains that were sealed with jute (a natural fiber) packing. This packing must be kept wet to prevent leakage. As cities were converted to natural gas, these mains were converted to natural gas service, and water foggers and other means were added to ensure packing integrity.”
ASME/CSD-1 Part CF-140, Drip Legs, states: “When a vertical section of piping supplied by the manufacturer is on the upstream side of the gas controls, a trap (drip leg) shall be included. When a vertical section of piping is not supplied, installation instructions shall require the installation of a trap at the inlet of the gas connection to the boiler.”

Part CF-140 is meant to prevent foreign particles from entering the fuel train and interfering with the proper operation of controls and safety devices.

However, the following requirements from the National Fuel Gas Code Z223.1/NFPA 54-2002 Edition, shed new light on the definitions. Section 8.5.7, Sediment Trap, states: “Where a sediment trap is not incorporated as a part of the gas utilization equipment, a sediment trap shall be installed as close to the inlet of the equipment as practicable at the time of installation. The sediment trap shall be either a tee fitting with a capped nipple in the bottom outlet as illustrated in Figure 8.5.7 or other device recognized as an effective sediment trap.”

Section 6.6.1, Provide Drips When Necessary, states: “For other than dry gas conditions, a drip shall be provided at any point in the line where condensation could collect. Where required by the authority having jurisdiction or the serving gas supplier, a drip shall also be provided at the outlet of the meter. This drip shall be so installed as to constitute a trap wherein an accumulation of condensation will shut off the flow of gas before it will run back into the meter.”

Section 6.7.2, Location of Drips, states: “All drips shall be installed only in such locations that they will be readily accessible to permit cleaning and emptying. A drip shall not be located where the condensation is likely to freeze.”

As can be seen from Figure 8.5.7 (Sediment Trap), Paragraph 6.6.1, and the two listed definitions, two entirely different devices are being addressed, each for a specific purpose and a specific location.

Based on the National Fuel Gas Code paragraphs and the two definitions provided above, CSD-1, Part CF-140 seems to confuse the two devices – a very common mistake. In fact, the sediment trap required by CF-140 is frequently and mistakenly referred to as a drip leg.

Even though drip traps and sediment traps are similarly constructed, it is important to keep the terms separate to avoid confusion.

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