Thermal processes are used to alter the physical, and sometimes chemical, properties of a material or coating. Two common examples of thermal processing would be high-temperature operations such as heat treating, and low-temperature operations, for instance drying or baking. Heat treating involves the use of heating or chilling, normally to extreme temperatures, to modify a material’s physical properties — making it harder or softer, for example. Many industries use baking, drying or other lower temperature heating processes to modify aspects of a material or coating. Additionally, facilities may have incinerators for oxidizing pollutants, or air heaters for tempering climate air. Applications for thermal processing are virtually endless.
At the heart of all thermal processes is a valve train (or fuel train or gas train). These fuel-delivery devices maintain consistent conditions of gasses into furnaces, ovens, dryers and boilers, among others, making them crucial in assuring safe ignition, operation and shutdown. Equally important, they keep gas out of the system whenever equipment is cycled or shut off.
Valve trains are critical to the operation of combustion systems. Despite being used daily in thousands of industrial facilities, awareness on their purpose and function may be dangerously absent because on-site training is minimal or informal. To many employees on the plant floor this series of valves, piping, wires and switches is simply too complex to take the time to understand. What is known can be dangerously misunderstood.
A valve train isn’t a single piece of equipment. Instead, it has many components including regulators, in-line strainers (“sediment traps”), safety shut-off valves (SSOV), manual valves (MV), pressure switches, and test fittings logically linked to a burner management system. Flame-sensing components make sure that flames are present when they are supposed to be, and not at a wrong time. Other components may consist of leak-test systems, gauges and pilot gas controls. At a minimum there are two crucial gas pressure switches in a valve safety train, one for low pressure and one for high pressure. The low gas pressure switch ensures the minimum gas pressure necessary to operate is present. As you would assume, it will shut off fuel to the burner if the gas pressure is below the setpoint. The high gas pressure switch ensures an excessive pressure is not present. It too will shut off fuel if the gas pressure is too high. Both switches must be proven safe to permit operation. Additionally, there will be an air pressure switch to ensure sufficient airflow is present to support burner operation. Some systems have supplementary pressure switches, such as a valve-proving pressure switch. Switches such as these are typically used to enhance safety or provide other safety aspects specific to that application’s needs. A multitude of sensors within the valve safety train — pressure switches, flame detectors, position indicators — and isolation and relief valves work together in concert to prevent accidents.
Valve trains must be compliant with all applicable local and national codes, standards, and insurance requirements. The most common of these for North America are NFPA, NEMA, CSA, UL, FM. Annual testing and preventive maintenance are not only an NPFA requirement, but also oftentimes required by insurance agencies, equipment manufacturers, and national standards, including ANSI, ASME, and NEC.
Understanding of fuel-fired equipment, especially the valve train, is necessary to prevent explosions, injuries and property damage. The truth is, although valve safety trains are required to be check regularly, they are rarely inspected, especially when maintenance budgets are cut. And while codes require training, they offer very little in terms of specific directions.
Don’t wait for a near miss or accident to inspect and/or upgrade your valve safety train. For more information on Rockford Systems Combustion Safety Solutions, please visit or call 1-800-922-7533