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Old 07-03-2013, 01:15 PM   #1
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Natural Gas Regulator 2 Mysteries


I recently did a complete overhaul of my natural gas distribution system. This is always a subject that generates discussion – should a DIYer try it or not? My conclusion is that if you are willing to do quite a bit of advance research (including reading up on code requirements), put an equal amount of time and energy into making a flow and pressure diagram (which involves many hours of consultation of flow and pressure tables), and then do the work slowly, carefully, and with LOTS OF LEAK TESTING, it is absolutely within the power of a reasonably handy DIYer.

But that aside, since I completed the project I’ve had two mysteries with my maxitrol line regulator. Any Sherlocks out there?

Mystery One: At one point the gas was off at the meter and the system was full of air. When the gas was turned back on at the meter, the gas was absolutely entering the regulator at 2psi (55 inches wc, I have a gauge) but the pressure coming out was ZERO – nothing coming out of the regulator at all (I have another gauge downstream of the regulator). To try something, I bled the line to the hot water heater – and that worked! The pressure coming out of the regulator went from zero to 9” wc and stayed there, just where it’s supposed to be.

Don’t get me wrong, I’m happy to take “yes” for an answer. But I’m very curious: Why on Earth would the regulator have not been putting out anything at all, and why would bleeding the line to the hot water heater solve the problem?

Mystery Two: After the water heater, I bled the line to the furnace. I ran into a little trouble there – after I tightened everything up, the leak solution showed evidence of a very tiny leak where the tube entered the fitting that goes into the valve at the furnace. It was a very, very small leak, but there is no such thing as an acceptable leak, so I took it apart and redid the connection…but that didn’t stop the leak. So I grabbed my wrenches and tightened the nut for everything I was worth, and succeeded in moving it about 1mm around. But that was enough! The leak solution showed no leak. Good as gold.

But the mysterious thing was, after I got the nut as tight as I could and stopped the leak, the pressure coming out of the regulator moved from an even 9 inches wc to 9.8 inches wc.

This leak was about as small as you could get -- just the smallest bubbles imaginable that formed slowly and few in number. Why would stopping a very, very tiny leak result in almost a full inch of change in pressure?

For the record, since these events, the pressures have been as steady as can be. 55 inches wc coming in, and 9.8 inches wc coming out.

Any ideas out there? And does anyone think the regulator might be damaged or defective?


Last edited by agd202; 07-03-2013 at 01:22 PM.
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Old 07-03-2013, 02:03 PM   #2
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Natural Gas Regulator 2 Mysteries


It sounds like a regulator problem as long as the gas was on and the regulator showed 0"wc on the supply side. I would have your gas company come and check the regulator, that is not something a DIY should do mainly because you do not own the regulator, the gas company does.

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Old 07-03-2013, 04:17 PM   #3
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Natural Gas Regulator 2 Mysteries


How much air pressure did you use.
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Old 07-03-2013, 08:59 PM   #4
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Natural Gas Regulator 2 Mysteries


Quote:
Originally Posted by agd202
Mystery One: At one point the gas was off at the meter and the system was full of air. When the gas was turned back on at the meter, the gas was absolutely entering the regulator at 2psi (55 inches wc, I have a gauge) but the pressure coming out was ZERO – nothing coming out of the regulator at all (I have another gauge downstream of the regulator). To try something, I bled the line to the hot water heater – and that worked! The pressure coming out of the regulator went from zero to 9” wc and stayed there, just where it’s supposed to be.

Don’t get me wrong, I’m happy to take “yes” for an answer. But I’m very curious: Why on Earth would the regulator have not been putting out anything at all, and why would bleeding the line to the hot water heater solve the problem?

Mystery Two: After the water heater, I bled the line to the furnace. I ran into a little trouble there – after I tightened everything up, the leak solution showed evidence of a very tiny leak where the tube entered the fitting that goes into the valve at the furnace. It was a very, very small leak, but there is no such thing as an acceptable leak, so I took it apart and redid the connection…but that didn’t stop the leak. So I grabbed my wrenches and tightened the nut for everything I was worth, and succeeded in moving it about 1mm around. But that was enough! The leak solution showed no leak. Good as gold.

But the mysterious thing was, after I got the nut as tight as I could and stopped the leak, the pressure coming out of the regulator moved from an even 9 inches wc to 9.8 inches wc.

This leak was about as small as you could get -- just the smallest bubbles imaginable that formed slowly and few in number. Why would stopping a very, very tiny leak result in almost a full inch of change in pressure?

For the record, since these events, the pressures have been as steady as can be. 55 inches wc coming in, and 9.8 inches wc coming out.

Any ideas out there? And does anyone think the regulator might be damaged or defective?
Mystery One: I won't bother asking you a million questions as to what you did, and I'll just make assumption for two possible scenarios. If you want to provide more info, feel free.

Scenario 1: you turned on the service regulator (the reg at the meter) too fast and shock loaded the system. This could do either blow your system reg, nothing, or, what you may have experienced- cause it to immediately lock up. The inlet pressure helps these regs lock up by pushing it from the bottom and plugging the orifice.

Scenario 2: while measuring flow, your gauge was too close to your bleed point. The velocity is greatest here, and thus the pressure will be least (look up Bernoulli effect). When you opened the bleed farther downstream at the water heater, your gauge was able to measure the actual pressure.

Mystery 2: when measuring pressure, it must be done at a constant flow. In other words, you want the gas to be flowing out of the same size orifice. Now, I kind of doubt that this small leak would affect the pressure much. What probably happened, was you stretched out the reg's diaphragm (the diaphragm is the measuring element of a regulator; when it gets stretched out it affects the proper measurement due to the increase in surface area) when you turned in the gas too fast (again, assuming) and it has recovered by the time you fixed the leak.

Always turn gas on and off slowly. Turning it on too quick shock loads the system and stretches the diaphragm. Turning it off too fast can have a similar but lesser affect, and can make your lock-up pressure appear too high.

Edit: I re-read your post. Mystery 2: when you had the leak, your reg wasn't locking up (stopping the flow gas-tight). 9.8" w.c. is your lock-up pressure. This is assuming that you were not flowing gas.

Last edited by hvac benny; 07-03-2013 at 09:37 PM.
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Old 07-04-2013, 03:36 PM   #5
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Natural Gas Regulator 2 Mysteries


I think you have it right for mystery 1. I'm now sure the gas poured into the line regulator at warp speed and caused it to lock up, thus no gas coming out. But I still don't get why bleeding the line to the hot water heater would cause the regulator to unlock.

And I like your idea about stretching the diaphram, though I'm not totally sold on it. But I wouldn't be suprised if both of these events were related.

Thanks for the reply and good ideas!
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