Combustible gas leak detection

[Bill Penn]

I have been using a Tiff8900 and have 3 times this year pointed out leaks to clients that when the HVAC guy arrives says there is no leak. Usually joints, or gas control valves. I have never been there at the time the HVAC guy is there.

Is there a possibility for a false positive? I just bought some bubble leak as a back up. But really, does that make sense? Using a $2 bottle of bubbles to confirm what your $200 tester indicated.

Any thoughts?

[Jimmy Roberts]

It does not matter what the bubbles cost, compared to the cost of the electronics. The bubbles are a physical indicator, and the bubbles don't care what your electronic toys have to say. If gas is escaping above atmospheric pressure, the bubbles will form, regardless of what the sniff test says. Maybe the HVAC tech simply does not consider the amount of gas being detected, to be a problem. If the HVAC guy says it's not a problem, recommend the client contact the gas utility for a FREE inspection. In fact, recommend a gas utility inspection as a matter of course, when a leak is detected.

[James Bohac]

Bill, Its not a bad idea to use another method to backup your initial findings! Could you detect a gas smell when you found the leaks?

[Rick Cantrell]

Have the unit tested and calibrated.

[Bill Penn]

About 1/2 the time I did smell gas.

You can't use bubbles on the burner supply fom the gas valve. I sometimes get an indication of gas leaking past the gas control valve. 1 HVAC tech said there will always be a residual amount of gas in the burner supply.

Seem's unreasonable. Thoughts?

[Rod Butler]

Residential gas lines usually run about 4 oz of pressure so if the bubble test fails I would say there is a leak.

[Bob Harper]

You need to do a search on this site as this has been discussed many times at length. You can get false positives from soap bubbles, pipe dope, thread cutting oil, greasy finger prints, etc.

[Nick Ostrowski]

My gas leak detector is my nose. I smell gas leaks quite often. At this mornings inspection, I pulled the access panel off off finished wall at the front of the basement and was immediately greeted with a big whiff of gas. The problem (for the home owner) was that the gas line penetrated the foundation wall at ceiling level and the access panel was at the bottom of the finished wall. He was going to have to open as much of the ceiling/wall area as necessary to have the leak fixed.

[Jerry Peck]

My gas leak detector is my nose. I smell gas leaks quite often.

My apologies ... I didn't realize you were standing there.:)

[Robert Ernst]

It is standard practice to use bubbles to check after the sniffer. I also don't check for leaks while the appliance is running.

[Jack Feldmann]

I use my nose first, then confirm with my Tiff. I will call utility myself if house is vacant.

[Vern Heiler]

Nose always knows and the gas detector is to pin point exact location. Soap is then used to verify. In Ontario with our extreme changes in temperature it is not uncommon for the fitting to the black iron main gas line to leak or even crack in movement but one can be fooled if you are not careful from residual smell on the venting. Key to success is always pin point the source.
Keven, can you expand on "residual smell on the venting"?

[Vern Heiler]

A pocket left by the natural venting can be detected and misconstrued as a leak. Just because you have a good nose to smell you still need to find the leak.
How to install a natural gas pressure regulator (http://www.lincenergysystems.com/linc-energy-blog/entry/how-to-install-a-natural-gas-pressure-regulator#.VQcLhI5LVTY)
The vent is there to sense the ambient pressure, which is how a regulator performs its magic. There is not suppose to be any leakage of gas. If you smell or detect gas at the vent, the diaphragm is leaking.

[Vern Heiler]

Correct! Relief is not leakage.
How much gas is allowed to "relief" to the atmosphere and where does it come from?

[Vern Heiler]

Did you read the link I provided?
Yes, but I did not see the answer to my questions.

- - - Updated - - -

I did read this,

Verify there are no leaks and all connections are tight.

[Vern Heiler]

They do vent when over pressure and are set to match the correct pressure. They will only relieve pressure when that pressure increases past the set amount. Never messure the gas at the vent unless you are sure it is a consistent leak.
There is no manufactured passage between the gas side and the atmosphere side of the diaphragm. If you smell gas there is a leak!

[Jerry Peck]

This is what Vern is explaining:
- https://www.youtube.com/watch?v=n4DDnoMAHY8

Generally good information, but incorrect on where to vent the regulator to :shocked: .

[Bob Harper]

ANSI z21.88 allows trace gas leakage at specific rates:
235cc/hr. through the main operator of the valve to the burner at 3/4 psi and 200 cc/hr. through the seals of the valve at 3/4 psi. Note that most gas appliance run at 1/4 psi or less inlet pressure.

Every time the pressure changes the diaphragm moves as it seeks to equalize against atmospheric pressure by the vent. Some trace leakage here is common. It mimics flatulence or a burp. A sustained gas discharge at a vent is a sign of a ruptured diaphragm. In that case, not only should the valve be replaced but the cause determined and corrected or you'll just have to replace another valve.

- - - Updated - - -

[Vern Heiler]

ANSI z21.88 allows trace gas leakage at specific rates:
235cc/hr. through the main operator of the valve to the burner at 3/4 psi and 200 cc/hr. through the seals of the valve at 3/4 psi. Note that most gas appliance run at 1/4 psi or less inlet pressure.

Every time the pressure changes the diaphragm moves as it seeks to equalize against atmospheric pressure by the vent. Some trace leakage here is common. It mimics flatulence or a burp. A sustained gas discharge at a vent is a sign of a ruptured diaphragm. In that case, not only should the valve be replaced but the cause determined and corrected or you'll just have to replace another valve.

- - - Updated - - -

ANSI z21.88 allows trace gas leakage at specific rates:
235cc/hr. through the main operator of the valve to the burner at 3/4 psi and 200 cc/hr. through the seals of the valve at 3/4 psi. Note that most gas appliance run at 1/4 psi or less inlet pressure.

Every time the pressure changes the diaphragm moves as it seeks to equalize against atmospheric pressure by the vent. Some trace leakage here is common. It mimics flatulence or a burp. A sustained gas discharge at a vent is a sign of a ruptured diaphragm. In that case, not only should the valve be replaced but the cause determined and corrected or you'll just have to replace another valve.
I am finding quite a few (est. 3-5%) MP regulator valves that are installed in attics leaking a small amount at the vent. I don't think I have found any leaking in a crawlspace. The furnace or water heater has not been firing at the time I have noticed the leaks. I can always smell the leak and then verify exact location with sniffer. Is the high temp of the attics causing the diaphragm to fail?

[Ken Rowe]

You guys realize this post is 3 years old, right?

[Jerry Peck]

ANSI z21.88 allows trace gas leakage at specific rates:
235cc/hr. through the main operator of the valve to the burner at 3/4 psi and 200 cc/hr. through the seals of the valve at 3/4 psi. Note that most gas appliance run at 1/4 psi or less inlet pressure.

Every time the pressure changes the diaphragm moves as it seeks to equalize against atmospheric pressure by the vent. Some trace leakage here is common. It mimics flatulence or a burp. A sustained gas discharge at a vent is a sign of a ruptured diaphragm. In that case, not only should the valve be replaced but the cause determined and corrected or you'll just have to replace another valve.

Bob,

Do you have a reference which addresses the venting pipe when the vent is extended to beyond a combustion/ignition source?

I.e., slope up or down (depends on propane or natural I suppose) or installing a trap in the vent (running across, down, across, back up, etc)