How utility natural gas regulators should work

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wwhitney

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I hear from a utility worker that I live on a city block where the natural gas distribution pressure is only 9"-10" w.c. There's some equipment on the corner he called the low pressure distribution equipment; it presumably drops the higher gas distribution pressure used elsewhere to the low pressure used on my block.

I'm also having a bit of trouble with hard starting on a Westinghouse sealed combustion condensing tank water heater. It's the only gas appliance on the residential gas service. As part of diagnosing that, I monitored the gas pressure just after the meter during a test cycle at the water heater. The results:

9.5" Pressure before starting
6.7" Brief drop at firing up
7.0" Steady state at high fire (76 kBTUs/hr)
7.2" Steady state at low fire (25 kBTUs/hr)
7.7" Initial pressure when off
9.5" Pressure slowly rises back over ~30 seconds

Now, I understand that a natural gas regulator will have a "lock-up" pressure when everything turns off that may be higher than the regulator outlet pressure at very low flow. But I would expect that to be a short term effect (<= 1 second), and that the jump I observed from 7.2" to 7.7" would reflect that behavior.

So the only reason I can see that the pressure slowly rises back to 9.5" over half a minute is that the regulator isn't closing fully, and the distribution pressure slowly bleeds through. The regulator is supposed to keep the downstream pressure at the 7.7" (in this example) even during no flow conditions, right?

If that's correct, I'll get in touch with the gas company about fixing/replacing the regulator. Just want to double check that the above behavior is abnormal and I'm not overlooking anything.

Thanks, Wayne
 

wwhitney

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TLDR:

Regular 7" w.c. residential natural gas service. If I shut off all the appliances and measure the pressure at the meter say 2 seconds later, I get 7.7" w.c. Wait 30 seconds and it's up to 9.5" w.c. Does that definitely mean the regulator is bad?

Thanks, Wayne
 
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Hey, wait a minute.

This is awkward, but...

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