Gas valve leaks

[2141]

I recently had a gas valve that was leaking through to the point of being able to smell it as you walk up to the furnace. This got me thinking that I should start checking for them on a clean and check using a leak detector. My question is at what point do you recommend replacing the gas valve? I checked one today(at the orifices) and my detector went off. I turned the gas cock off and waited 30minutes or so and checked again and it still went off. Not sure if I'm getting false positives or its residual. Anyone have any tips? I don't want to rip anyone off ya know

[jtrammel]

Sounds like false readings, soap bubbles don't lie.

[chevster01]

hey if its leaking you replace it. You are not ripping him or her off, you are probably saving their lives. Also try using soap bubbles or some of that leak detection fluid in case your detector is malfunctioning. If there is a leak around those orifices you will see it.

[gravity]

easy way to check is with a combustion analyzer on shutdown.

ive also had the pilot valve leaking while no call for heat active. this was a spark ignition setup.

[beenthere]

Gas valve is allowed to leak 200CCM(0.007062933 CF) an hour as I recall.

[54regcab]

hey if its leaking you replace it. You are not ripping him or her off, you are probably saving their lives. Also try using soap bubbles or some of that leak detection fluid in case your detector is malfunctioning. If there is a leak around those orifices you will see it.

Soap bublles are something you can show the customer also.

[hearthman]

ANSI stds allow trace gas leakage through the seals of the valve into the room at 200cc/hr and 235 cc/hr through the main operator to the burners both at 3/4 psi.

[2141]

Gas valve is allowed to leak 200CCM(0.007062933 CF) an hour as I recall.

So how do you measure this? I was told by one of our senior techs that you are supposed to put a manometer on and block the orifices. if it goes to .5"h2o in 5minutes then recommend a new valve and if it makes it to 1" in ten minutes then it needs to be turned off and red tagged. Any thoughts on this?

[beenthere]

The size of the manifold would also play a large roll in how long it takes to build up to X pressure.

[Nytefog]

While operating the system with a combustion analyzer close the gas valve. Watch the CO reading. If it rises after the gas valves is closed then the valve is leaking. I mean if it goes up a few ppm then i wouldn't be worried, but if it spikes up a good amount its time to replace the gas valve.

Any type of CO or gas/oil issues i always recommend repairing the issue to prevent any bad happens and you are sued. Same goes with any type of saftey limit, delayed ignition or vent piping issues.

You have to be crazy not to especially wiht people looking for a reason to sue. If customer refuses repair i make sure i have potential injury and death that could happen and make them sign that they understand the issues.

[catmanacman]

you will always detect at the orfice ,check it with bubbles

[Hvac216]

While operating the system with a combustion analyzer close the gas valve. Watch the CO reading. If it rises after the gas valves is closed then the valve is leaking. I mean if it goes up a few ppm then i wouldn't be worried, but if it spikes up a good amount its time to replace the gas valve.

Any type of CO or gas/oil issues i always recommend repairing the issue to prevent any bad happens and you are sued. Same goes with any type of saftey limit, delayed ignition or vent piping issues.

You have to be crazy not to especially wiht people looking for a reason to sue. If customer refuses repair i make sure i have potential injury and death that could happen and make them sign that they understand the issues.

Can you explain this a little more please? Do you shut it off at the gas cock, or the gas valve itself? Are you watching co, or co air free? And why would gas leaking cause co to rise?

[hearthman]

So how do you measure this? I was told by one of our senior techs that you are supposed to put a manometer on and block the orifices. if it goes to .5"h2o in 5minutes then recommend a new valve and if it makes it to 1" in ten minutes then it needs to be turned off and red tagged. Any thoughts on this?


Well, it's done in the lab with a bubble-o-meter attached to the valve discharge for through the main operator and before the valve with the gas turned off for leakage through the valve seals. http://www.bubble-o-meter.com/index.php

Correct info. on using CA and valve failing to close to a point. You can also use a gas sniffer or manometer at the gas valve outlet and kill the power then see if you still detect gas. Bubble meter is lab certified accuracy and quantitative. Careful with soap bubble solutions: must be non-corrosive and never painted over the vent on a gas regulator. Use sniffer. If steady leak at vent, indicates blown diaphragm, possibly from overpressure.

[Nytefog]

Can you explain this a little more please? Do you shut it off at the gas cock, or the gas valve itself? Are you watching co, or co air free? And why would gas leaking cause co to rise?


You shut the gas valve switch to the off position while their is still a call for heat. The CO rises because the unburn gas is traveling through a hot heat exchanger causing it to produce CO from inadequate combustion. Just as if you were to take a reading on a overfired furnace. Incomplete combustion. Doing the reading with the analyzer is just a easy test to perform at the end of your combustion analysis after tuning the furnace to double check the saftey of the gas valve. I would use a combustable gas leak detector if i were only there to check to see if the GV was leaking.

You should take Jim Davis's class offered by NCI. It will open you eyes. Best class i've ever taken hands down.

I am watchin CO. I never watch CO AF. Tha is just a calculation. CO is the actual reading of the amount of CO present in the flue gas..