Rotary airlock valves are an asset to NFPA safety, but they must also be maintained and handled with care.
With all the moving parts in a material conveying system, manufacturing workers must take unique precautions with each piece of machinery in the line — including the rotary valve. They also have to stay vigilant about combustible dust and the fire hazard it poses in any given facility.
According to an NFPA report, U.S. municipal fire departments responded to an average of 37,910 fires at industrial or manufacturing facilities each year between 2011 and 2015. In 2018, the U.S. Bureau of Labor estimated a total of 430,300 nonfatal injuries in the manufacturing sector.1
Rotary airlock valves play an important role in fire safety, but they must also be maintained and handled with care. Manufacturers should understand how valves contribute to NFPA compliance, how to identify a valve built with all the necessary safety features, what safety precautions to teach their workers, and how to keep valves in safe working order with proper maintenance.
A Valve’s Role in NFPA Compliance
Whether manufacturers convey flour, sugar, cement, or something else entirely, their materials often create dust. When too many dust particles accumulate on surfaces or in the air around a conveying system, they can become a fuel source that ignites a fire or explosion in the facility. In a case like that, a rotary valve helps in several ways. A high-quality, well-maintained valve prevents dust from leaking out into the facility where it can catch fire. If a fire does break out somewhere in a conveying system, the valve acts as an isolation device that cuts off oxygen and stops the spread of flames.
For those functions to work, plant ventilation is critical. If a pressure conveying system is not well-ventilated, air will travel back up into the hopper and potentially release material dust into the workplace. A rotary valve with high-quality construction and safety features goes a long way to protecting workers on the shop floor.
What Does a Safe Valve Look Like?
For manufacturers in the market for new equipment, there are a few key ways to ensure a valve is built to proper standards. Not all suppliers sell NFPA-compliant valves as a standard. In fact, they often charge a fee for safety features that ought to be mandatory.
Several key components of valve safety involve the rotor. An NFPA-compliant rotor should have at least two vanes in contact with each side of the valve housing at all times — an 8-vane rotor is recommended. Avoid rubber rotor tips in favor of steel, and make sure the rotor blade is 3/8in. thick.
Outboard bearings (as opposed to inboard bearings) are mandatory under NFPA 69 and 654. That’s because outboard bearings, located on the outside of the valve housing, are kept away from the constant stream of combustible dust going through the valve. It’s also easier to inspect, clean and maintain outboard bearings because workers don’t need to access the valve’s internals.2
For added safety, some valves can be equipped with flange guards at the inlet and outlet. These guards block access to dangerous moving parts and prevent workplace injuries.
Quick Tips to Keep Workers Safe
Manufacturers must take precautions to ensure their valve and conveying systems are safe, but workers should know proper safety procedures as well. Consult this quick list of best practices to help everyone minimize hazards on the shop floor:
- Follow proper lockout/tagout procedure.
- Document all repairs, maintenance, and checks in a historical maintenance log.
- Measure rotor-to-housing tolerances regularly and make any necessary rotor replacements.
- Avoid pinch points and shear points — places where exposed moving parts pose a risk of injury.
- Release process pressure from the valve before opening it for maintenance.
- Ground conveying systems with copper wire to reduce the risk of electric shock.
- Clean equipment regularly and keep it free of combustible dust.
- Make sure your plant is properly ventilated.
Rotary valve orders should come with a maintenance or installation manual that outlines all the proper, valve-specific procedures in detail.
Key Maintenance Considerations for Safety
In manufacturing, the words “historical maintenance log” are gospel. Maintenance should be performed regularly and logged so that all staff can see what work has been done on the valve.
When it comes to safety, one of the most important maintenance checks is rotor-to-housing tolerance. For a new valve, it is recommended that workers measure the clearances, or gaps, between the rotor and housing to ensure they are not too large. The gap should be no larger than 0.079 in. to ensure the valve always performs as it should and stays NFPA compliant. Otherwise, material may escape through the gaps and create a combustible dust hazard.
When clearances are too large, it’s time to replace the rotor. The gaps should be checked every three months at first. If the clearances are consistently fine within that time frame, manufacturers can test them every four or five months to see if that’s a more efficient schedule.
For those in sanitary industries such as food manufacturing and pharmaceuticals, cleaning should already be a regular part of a valve’s maintenance routine. This will minimize any potential dust accumulation. Proper cleaning will also extend the lifespan of the valve and its related parts, minimizing the chance that something will malfunction. A rotary valve built on rails makes all of those tasks — cleaning, tolerance checks and maintenance — much faster and easier.3
Find a Partner in Valve Safety
From 2003 to 2017, the number of fatal work injuries in private manufacturing has gone down 28 percent. While the rate of workplace fatalities and injuries in manufacturing has steadily declined over the years — thanks to improving practices and tightening regulations — there’s always room for companies to improve their safety practices and minimize risk. When it comes to rotary valves, a safer choice starts with a reputable supplier. Companies would do well to trust in valve manufacturers that take the time to recommend safety features, explain best practices, and build NFPA-compliant valves at no additional cost.
Megan Thompson is president and COO of ACS Valves (Caledonia, ON, Canada), a leading rotary valve manufacturer. Thompson is responsible for directing the company’s global operations, sales, marketing, and product development initiatives. She is also ACS' resident NFPA expert and often advises customers on ways they can prevent fires, explosions, and other dangers in their manufacturing facilities. For more information, call 905-765-2004 or visit www.acsvalves.com.
Here is another article that may interest you: