Does your manufacturing facility have a smoke stack? If it does, your facility also likely contains a valve train, commonly known in industrial circles as a “gas train” or a “fuel train.” This complicated series of piping and components requires annual inspections, accurate record keeping and preventive maintenance to avert productivity issues.

“If you aren’t sure what a valve train is, you’re not alone. It is one of the most misunderstood pieces of equipment on the plant floor,” said Robert Sanderson, P.E., director of business development at Rockford Combustion Systems, a division of Rockford Systems LLC. “As a result, the valve train rarely receives the consideration it should from thermal combustion professionals.”

Sanderson notes that while it isn’t necessary to know every engineered component of a valve train, you should be aware of what it does and why it demands your organization’s attention. Essentially, a valve train controls the flow of fuel into thermal-processing equipment. By controlling the desired ratio of fuel and air, the connected burner then properly oxidizes the mixture, safely releasing the energy needed to heat your furnaces, boilers, thermal oxidizers and other equipment. In turn, the thermal-processing equipment performs critical production tasks such as heat treating metals, fluid heating and pollution control.

Owing to the presence of hazardous vapors and gases, poorly designed or inadequately maintained valve trains have led to fires and injuries. Thankfully, you can significantly reduce the potential for mishaps by asking your plant manager these five simple questions.


1. Does the valve train receive an annual inspection?

The entire combustion system must be inspected at least annually to ensure compliance. NFPA 86 standards provide guidelines to establish these measures, stating: “The user has the responsibility for establishing a program of inspection, testing and maintenance with documentation performed at least annually.” This applies to both new installations and modifications. Annual testing is typically required by insurance agencies, but other (often overlapping) codes and standards may need to be adhered to in addition to NFPA (e.g., ANSI, ASME, NEC and the EPA).

“If your organization does not possess the expertise, a qualified contractor could perform annual inspections,” Sanderson said. “The contractor will test, assess, maintain and replace necessary components of the gas train, leaving your organization with a system that is code-compliant. In addition, accurate record keeping by both the contractor and your maintenance team will allow you to follow trends in train performance.”


2. Is the combustion system being correctly purged?

A purge cycle ensures that flammable vapors or gases that might have entered the equipment are cleared. This is important to make sure conditions are safe before intentionally lighting the fuel. Three basic requirements must be satisfied: combustibles feeding the process have been isolated, purge airflow is maintained and purge time is completed.

Interlocked switches on the valve train ensure fuel is not entering the system when off. Purge airflow may be verified by using a flow-metering device or by measuring a fixed drop in pressure. The final requirement is verifying the purge timer, which is set for the time it takes to clear the system of combustible mixtures. The purge time is determined by the volume of the equipment and is at least four system volumes. Controls continuously monitor the purge airflow and timing. If anything is interrupted, a restart and a new full purge must be performed.


3. Are any components missing?

As mentioned earlier, valve trains are complex and comprised from a series of components, each dependent on the last. Even the most basic combustion system will feature shut-off valves, manual shut-off valves, high- and low-pressure switches, pressure taps, and in-line strainers. Add to this regulators, valve leak-test systems, diagnostic gauges and pilot accessories, and one quickly recognizes the potential for missing parts – either by design or accident. Your plant manager’s maintenance records should indicate if alterations to the original equipment were made.

One frequently missing component of the valve train is the sediment trap. Sediment traps should be installed beneath incoming vertical drops to capture large debris and pipeline condensate. While sediment traps effectively prevent contaminants from getting into the gas equipment and are required by NFPA, many manufacturers do not include them unless specified.

Another frequently non-compliant device is the gas-pressure switches. Found in pairs, these switches monitor and ensure the fuel pressure remains within a safe operating window. However, these switches are often bypassed, improperly set or incorrectly installed.

“An untrained maintenance team member may inadvertently bypass or adjust a switch to get equipment running immediately,” Sanderson said. “Switches that are bypassed or set to impossible pressures provide no protection whatsoever. Additionally, these switches must be electrically sealed to preclude explosive vapors from flowing backward through the wiring system.”


4. Is the valve train vented or ventless?

Unless valve train components are listed as “ventless,” vent lines are necessary. Simply installing vent piping is often insufficient. Vent lines must be correctly engineered, installed and routed to appropriate and approved locations to be effective. Even when vent lines are properly installed, building pressures can vary sufficiently and may prevent optimal burner performance. Vent pipes have also been known to fill with spiders, bees and other nesting insects. Once plugged, the pipes will impede the escape of gases, which leads to a potential gas buildup inside the facility.

In short, vent lines are another potential failure point. Vents must be inspected regularly by maintenance staff for leaks or blockages. Always go with ventless components when given the choice.


5. Are emissions being controlled?

Emission compliance is a major focus in many industries and geographical regions, such as California. Is your plant compliant with the appropriate regulations? If not, agencies may issue hefty fines or shut down production completely until modifications are made. A simple burner tuning will sometimes ensure a system operates within requirements. At other times, meeting new EPA or revised local requirements necessitates modifications to existing valve trains since installing a low-NOx burner often creates the need for improved fuel-control.



Learning about and acting on the potential dangers of valve trains and scheduling annual inspections will help reduce risks and improve productivity in your organization. Find the valve trains in your plant and have a look at them. Can you find evidence of inspection, such as documentation, stickers in the control box or other supporting paperwork? Do the shut-off valves have fittings for testing?

If you cannot find evidence of a recent annual inspection, do not risk becoming a statistic. Instead, have a conversation with your plant manager or maintenance team lead.


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