Tighten Up, Part 1
The valves are key players in the protection against explosions and fires. In fact, each safety shutoff valve is required to discontinue the fuel flow to a burner system after interruption of electric current or fluid pressure. Electric current or fluid pressure can be interrupted by interlocking safety devices, combustion safeguards or operating controls. Because they are designed to discontinue the flow of fuel to a system and in turn protect against explosions, these valves must be checked for leaks and tightness as prescribed by NFPA 86 5-7.2.4. According to Franklin Switzer of Maxon Corp., Muncie, IN, this very important section of NFPA 86 is too often ignored. Like any mechanical device, environmental conditions and corrosive materials in the gas stream can gradually compromise the valve's performance.
Why Not Check Valve Tightness?Section 5-7.2.4 states that tightness checks must be performed in accordance with the manufacturer's instructions and that testing frequency must be at least annually - that is, at least once per year. However, Switzer believes there are a number of 20- and 30-year-old systems in operation that have never been tested for leaks. With proper pre-ignition purging with air, neglecting to check safety shutoff valves for tightness has not caused many accidents. But, any accident involving explosive gases can be catastrophic, resulting in property damage, injury and even death. So, why don't users perform tightness checks? Dick Bennett of Janus Technology Group, Rockford, IL, believes part of the reason is because upper management doesn't require it. According to Jim Roberts, Eclipse Combustion, Rockford, IL, most valves do not get checked because the user has not implemented a maintenance or safety plan and adhered to it. He believes the hard truth is that many facilities ignore valve maintenance and training issues.
As systems and components age, the risk of a valve accident increases. This is not to say that just because a component is old it should be replaced, but it should be tested. According to John Clarke of Maxon, if the valve has been checked and is functioning properly, it can continue to work properly for a number of years. If it is never checked and is left alone to run for years on end, how can you be sure that it is working properly? How do you know that tomorrow isn't the day that the valve fails and you experience a fire or explosion?
Performing Tightness and Leak ChecksTo comply with NFPA, a leak test must be performed per manufacturer's recommendations at least once per year. A manual bubble check is the most common method for leak checking valves. These checks require sampling taps for bubble tubes downstream of the safety shutoff valve as well as special electrical circuitry to conduct the test. Many times, taps are present, but the electrical circuitry is absent, preventing testing from taking place.
There are some valve proving systems that perform a check of the valves each time the system is energized. While they do enhance safety, they seldom are applied to checks to ensure the valve performs to its original specifications. They also do not absolve a user from performing annual leakage checks.
Like every other rule, NFPA 86 has some exceptions. In next month's column, I'll look at the exceptions related to testing safety shutoff valves.