As a design engineer responsible for developing and specifying boilers, dryers, furnaces, heaters, ovens and other industrial heating equipment, you face a daunting labyrinth of standards and industry regulations. Regulatory bodies sound a bit like alphabet soup, with acronyms like UL, FM, CSA, UR, AGA, ASME, ANSI, IRI, CE and NFPA tossed about. This article will help explain a common task for many thermal processing equipment specifiers: meeting the requirements of key codes — including Underwriters Laboratories (UL), Factory Mutual Insurers (FM) and the National Fire Protection Association (NFPA) — for safety valve equipment used in process heating applications.

Click here to see the Valves Codes & Standards table.

Ensuring Safety via High Reliability Valves

Key to designing safety into your fuel train configurations are familiar technologies such as safety shutoff valves and vent valves as well as visual-indication mechanisms and proof-of-closure switches.

Your design skills come into play with how you take advantage of the wide range of products available. You can mix and match solenoid and safety shutoff valves — within designs from catalytic reactors to multi-zone furnaces — to create easily installed, cost-effective solutions that comply with all necessary standards. (See table.)

Make sure, however, that you start with a good grasp of valve element fundamentals. For example, examining a proof-of-closure (POC) switch underlines how reliably modern valves can ensure combustion safety. The POC unit provides an electrical contact interlocked with the controller safety circuit. In a typical design, the switch is located at the bottom of the valve, positioned to trace the stroke of the valve disc. When the disc seal reaches the fully closed position, it triggers the mechanism to push down on the contact, closing it and triggering the unit’s visual indicator to show open or closed status. As a result, the operator can act with full confidence in situations where it is critical that a safety valve be safely closed.

To provide ease of installation, many users prefer valves with modular capabilities. For example, to reduce mounting complexity, you can choose modular gas safety shut-off valves — combining a solenoid valve with an electrohydraulic motorized valve for a compact double-valve footprint, a slow-open feature and high flow rates. An accompanying actuator can provide on/off or high/low/off firing rates as well as visual indication and proof of closure for compliance with most industry standards.

Also, you may want to look for valves that include useful features such as pipe taps, which can facilitate accurate pressure readings and leakage testing.

High reliability valve components like these are available to meet a many standards, including those shown in the sidebar.

Knowing your valve choices — and how they meet given codes and standards — can reduce the time required for design and production while facilitating compliance. This results in safer, more efficient and cost-effective heating process installations. 

Chart

Valve Codes and Standards: Typical Fuel-Train Installation Sizes

Under 150,000 BTU/hr

NFPAFor fluid heaters under 150,000 BTU, NFPA requires two safety shutoff valves.

Under 400,000 BTU/hr

FMFor installations in this range, FM requires one safety shutoff valve equipped with visual indication. This covers several types of equipment under several standards: Gas-fired, single-burner boilers and furnaces; space heaters, including unit, radiant, duct furnace, makeup air and rooftop types; and industrial ovens and dryers. Valves should be approved for FM Class 7400 liquid and gas safety shutoff.

NFPAFrom 150,000 to 400,000 BTU, NFPA mandates two safety shutoff valves equipped with visual indication. For furnaces of 150,000 BTU or more, it requires two safety shutoff valves equipped with visual indication. NFPA does not cover boilers in this category.

From 400,000 to 2,500,000 BTU/hr

ULUL requires two safety shutoff valves or one safety shutoff valve equipped with visual indication and a proof-of-closure switch. This covers gas burners, heating furnaces and boilers (except process equipment).

FMFor relevant units except industrial ovens and dryers, FM requires two safety shutoff valves equipped with visual indication or one safety shutoff valve equipped with visual indication and a proof-of-closure switch. It mandates the above choice (two safety shutoff valves equipped with visual indication, or one safety shutoff valve equipped with visual indication and a proof-of-closure switch), also for space heaters, including unit, radiant, duct furnace, makeup air and rooftop types. Valves should be approved for FM Class 7400 liquid and gas safety shutoff. However, for industrial ovens and dryers, FM follows NFPA.

NFPANFPA requires one safety shutoff valve equipped with visual indication and one safety shutoff valve equipped with visual indication and a proof-of-closure switch. This also applies to furnaces, and it mandates position indication for safety shutoff valves to burners or pilots. NFPA does not cover boilers in this category. For fluid heaters over 400,000 BTU, NFPA mandates one safety shutoff valve equipped with visual indication and one safety shutoff valve equipped with visual indication and a proof-of-closure switch.

From 2,500,000 to 5,000,000 BTU/hr

ULUL requires two safety shutoff valves or one safety shutoff valve equipped with visual indication and a proof-of-closure switch. This covers gas burners, heating furnaces and boilers (except process equipment). Valves are certified as UL429 electrically operated valves.

FMFor relevant units, except industrial ovens and dryers, FM requires two safety shutoff valves equipped with visual indication or one safety shutoff valve equipped with visual indication and a proof-of-closure switch. This covers gas-fired, single-burner boilers and furnaces and space heaters — including unit, radiant, duct furnace, makeup air and rooftop types. Valves should be approved for FM Class 7400 liquid and gas safety shutoff. For industrial ovens and dryers, however, FM follows NFPA.

NPFANFPA requires one safety shutoff valve equipped with visual indication and one safety shutoff valve equipped with visual indication and a proof-of-closure switch. This also applies to furnaces, and mandates position indication for safety shutoff valves to burners or pilots. NFPA does not cover boilers in this category.

From 5,000,000 to 12,500,000 BTU/hr

FMFor gas-fired, single-burner boilers and furnaces, FM requires one safety shutoff valve equipped with visual indication and one safety shutoff valve equipped with visual indication and a proof-of-closure switch. This covers gas-fired, single-burner boilers and furnaces and space heaters — including unit, radiant, duct furnace, makeup air and rooftop types. It also mandates position indication for safety shutoff valves to burners or pilots. Valves should be approved for FM Class 7400 liquid and gas safety shutoff. For space heaters, including unit, radiant, duct furnace, makeup air and rooftop types, FM mandates two safety shutoff valves equipped with visual indication or one safety shutoff valve equipped with visual indication and a proof-of-closure switch. For industrial ovens and dryers, FM follows NFPA.

NFPANFPA requires one safety shutoff valve equipped with visual indication and one safety shutoff valve equipped with visual indication and a proof-of-closure switch. This also applies to furnaces and it mandates position indication for safety shutoff valves to burners or pilots. NFPA does not cover boilers in this category.

More than 12,500,000 BTU/hr

ULUL requires one safety shutoff valve, one safety shutoff valve equipped with visual indication and a proof-of-closure switch and one vent valve. This covers gas burners, heating furnaces and boilers (except process equipment). Valves are certified as UL429 electrically operated valves.

FMFor gas-fired, single-burner boilers and furnaces, FM requires two safety shutoff valves equipped with visual indication and proof-ofclosure switches. It also mandates position indication for safety shutoff valves to burners or pilots. Valves should be approved for FM Class 7400 liquid and gas safety shutoff.

FM con'tFor space heaters, including unit, radiant, duct furnace, makeup air and rooftop types, FM mandates one safety shutoff valve equipped with visual indication and one safety shutoff valve equipped with visual indication and a proof-of-closure switch. FM also requires this arrangement for industrial ovens and dryers.

NFPANFPA requires one safety shutoff valve equipped with visual indication and one safety shutoff valve equipped with visual indication and a proof-of-closure switch. This also applies to furnaces and it mandates position indication for safety shutoff valves to burners or pilots. For both single-burner and multiple-burner boilers, NFPA requires two safety shutoff valves equipped with visual indication and proof-ofclosure switches and one vent valve.