Understanding the Boiler Gas Train

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Understanding the Boiler Gas Train

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Ryan_19

What is the purpose of the main gas vent valve and the pilot vent valve? I understand that they vent the gas to the atmosphere when the main gas valves and the pilot valves close, but why do you need to vent the gas?

Thanks,
Ryan

RayWohlfarth

Ryan, I believe you are referring to the vent pipe from the gas train components. They are used to vent the natural gas if the rubber diaphragm inside the gas pressure regulator or gas valve splits or cracks. They are to be vented outside. If they are not vented, a 1/4" fitting leaking could fill a boiler room with a combustible mixture in a relatively short time making it very dangerous. Hope this helps.
Ray

Hulk

We bought a dry cleaner and I'm coming up to speed quickly fixing all the machines incl. two 15 HP Fulton boilers. One problem we've had is we smell gas in the plant, yet the gas co. checked all the pipes and said there were no leaks. There's a leak we smell it. Today I tried to find the leak myself when I noticed a stronger smell of gas in the intake air vent. There is a 1/4" gas line feeding all the way up the vent pipe to the roof. As you feel the air coming in on your face you smell the gas. So I've been trying to figure out why there is this gas line coming from the gas train and why it would have a constant small leak. Based on this post in 2016 by Ray it seems that one of my main gas valves must need to be replaced, as it sounds like the only time this 1/4 in line should vent gas is when the rubber diaphragm inside the gas valve cracks. Please let me know if I'm on the right track and if there is a way to be certain as I'm sure main gas valves are expensive.
Thank you

EBEBRATT-Ed

Excellent explanation @RayWohlfarth

The block and bleed and normally open solenoid valve used to be required by FIA (Factory Insurance Association) now known as IRI (Industrial Risk Insurers) The used to be the most strict code. Next was FM (Factory Mutual) Then there is UL and probably many others depending on the job location. And many states have different requirements

retiredguy

Well done @Ray Wohlfarth

Your explanation was spot on and is the way it was when I retired in 2007. The "codes" were always changing due to some VIP thinking that he was saving the world. My 1 big "pet peeve" was the N/O vent valve between the two gas valves. To me that was a waste of time and money. On a couple jobs it actually caused a problem by the upstream gas valve not closing properly and venting the gas into the atmosphere and which entered the air stream and was sucked into the building through a univent. The place that I remember this best was at a school in Green County, Pa. The school was evacuated until the problem was corrected.

On a very few jobs a "proof of closure" and/or a "proof of open" switch was also required. There were even a few instances where the 2 gas valves could not be of the same design and they also required 2 pilot solenoid valves. When you read all the requirements of the IRI code your head would explode from all the non-sense. They wanted to dictate the number of air changes through the boiler during the pre-purge before the pilot lit. I could go on but why?

EBEBRATT-Ed

@retiredguy

Nothing like working on a burner with the 90 second pre purge. Trying to trouble shoot too forever. The old Fireye 6070 you could crank the timer manually to speed things up. The electronic controls you had to sit their and ..........wait