Five Questions to Ask Your Plant ManagerAbout Valve Trains
If you aren’t asking these questions, your fuel-fired equipment may not be operating at peak performance.
By Robert Sanderson P.E.
Does your manufacturing facility have a smokestack? 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 require annual inspections, accuraterecord-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 equipmenton the plant floor. As a result, the valve train rarely receives the consideration it should from thermal combustion professionals.
While it isn’t necessary to know every engineered component of a valve train, you should be aware of what it doesand why it demands your organization’s attention. Essentially, a valve train controls the flow of fuel into thermalprocessing equipment. By controlling the desired ratio offuel and air, the connected burner then properly oxidizesthe mixture, safely releasing the energy needed to heat yourfurnaces, boilers, HVAC heaters, thermal oxidizers, andother equipment. In turn, the thermal process equipmentperforms critical production tasks such as drying gypsumboards, roasting and baking foods, heat-treating metals, fluid heating, and pollution control.
Owing to the presence of hazardous vapors and gases,poorly designed or inadequately maintained valve trains haveled to fires, multi-million dollar losses, and injuries. Thankfully, you can significantly reduce the potential for mishapsby asking your plant manager these five simple questions:
1. Does the Valve Train Receive an
The entire combustion system must be inspected at leastannually to ensure compliance. NFPA 86 standards provideguidelines to establish these measures, stating, “The user hasthe responsibility for establishing a program of inspection,testing, and maintenance with documentation performed atleast annually.” This applies to both new installations andmodifications. Annual testing is typically required by insurance agencies, but other (often overlapping) codes andstandards may need to be adhered to besides NFPA, for example, ANSI, ASME, NEC, and the EPA. Oil-fired burnersmust comply with UL-296 Standard for Oil Burners, UL-726 Standard for Oil-Fired Boiler Assemblies, or UL-2096Standard for Commercial/Industrial Gas and/or Oil-Burn-ing Assemblies with Emission Reduction Equipment.
If your organization does not possess the expertise, aqualified contractor could perform annual inspections.The contractor will test, assess, maintain, and replacenecessary components of the gas train, leaving your organization with a system that is code compliant. In addition, accurate record-keeping by both the contractor andyour maintenance team will allow you to follow trends intrain performance.
2. Is the Combustion System Being
A purge cycle ensures that flammable vapors or gases thatmight 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 notentering the system when off. Purge airflow may be verifiedby using a flow-metering device or by measuring a fixeddrop in pressure. The final requirement is verifying thepurge timer, which is set for the time it takes to clear thesystem of combustible mixtures. The purge time is determined by the volume of the equipment and is at least foursystem volumes. Controls continuously monitor the purgeairflow and timing. If anything is interrupted a restart anda 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 thelast. Even the most basic combustion system will featureshut-off valves, manual shut-off valves, high- and low-pressure switches, pressure taps, and in-line strainers. Add to thisregulator, valve leak-test systems, diagnostic gauges, and pilot accessories and one quickly recognizes the potential formissing parts either by design or accident. Your plant manager’s maintenance records should indicate if alterations to theoriginal equipment were made.
One frequently missing component of the valve train isthe sediment trap. Sediment traps should be installed beneath incoming vertical drops to capture large debris andpipeline condensate. While sediment traps effectively preventcontaminants from getting into the gas equipment and arerequired by NFPA, many manufacturers do not include themunless specified.
Another frequently non-compliant device are the gas-pres-sure switches. Found in pairs, these switches monitor and ensure the fuel pressure remains within a safe operating window. Often, however, these switches are bypassed, improperlyset, or incorrectly installed.
An untrained maintenance team member may inadvertently bypass or adjust a switch to get equipment runningimmediately. Switches that are bypassed or set to impossible pressures provide no protection whatsoever. Additionally, these switches must be electrically sealed to precludeexplosive vapors from flowing backward through the wiring system.
4. Is the Valve Train Vented or Ventless?
Unless valve train components are listed as “ventless,” ventlines 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 that may prevent optimalburner performance. Vent pipes have also been known to fillwith spiders, bees, and other nesting insects. Once plugged,the pipes will impede the escape of gases, leading to a potential gas build-up inside the facility.
In short, vent lines are another potential failure point.Vents must be inspected regularly by maintenance staff forleaks or blockages. When given the choice always go withventless components.
5. Are Emissions Being Controlled?
Emission compliance is a major focus in many industriesand geographical regions, such as California. Is your plantcompliant with the appropriate regulations? If not, agencies may issue hefty fines or shutdown production completely until modifications are made. Sometimes, a simpleburner tuning will ensure a system operates within requirements. At other times meeting new Environmental Protection Agency (EPA) or revised local requirements necessitate modifications to existing valve trains, since installinga low NOx burner often creates the need for improved fuelcontrol too.
Robert Sanderson, P.E., Director of Business Development at RockfordCombustion Systems—a division of Rockford Systems, LLC—is a registeredProfessional Engineer with an excess of 25 years of industry experience.
Credit: Rockford Combustion Solutions