Generac Natural Gas Line

[fostercontractors]

Thanks for the opportunity to post this question here!

In 2022 I installed a 14kw Generac standby -plumber installed a 1.25" poly gas line 40 feet with two risers and full port valves on each end, it passed pressure tests, instapection and we put the generator into service. About 6 mos or so later I noted the rpm's not perfectly smooth at weekly exercise and didn't pay much attention until it seemed to get slightly worse. The condition was (and remains) very similar to what a gas engine sounds like when you've rebuilt the carb and don't have the fuel mixture screw adjusted just right -sounds like it's trying to find a bit more fuel, aka "hunting", aka "surging". Many would not hear the condition, me and all the Generac techs that have tried to remedy it can hear it very well. Condition doesn't change under load.

Generac techs and Generac decided it was a cylinder head issue and replaced the engine under warranty. No change.
Same techs were told to replace lifters (hydraulic) on the new engine. No change.
New tech swapped a new control board, updated software, swapped air filter, onboard regulator, stepper motor. No change.

Gas pressure at the genset is still within specs 7 WC at rest and 6.5 WC at idle. Gas utility came out this week to verify gas pressure and possible contamination. He measured 4oz pressure and after purging the air he showed me the gas analyzer readings were 100% purity at the genset, at my gas range and at my water heater.

Generac techs say it HAS TO BE A GAS ISSUE.

Gas utility tech says GAS SYSTEM INTEGRITY IS 100%, NO LEAKS, PERFECT PRESSURE

My questions for you gas line gurus is this: Is there any remote possibility that my underground gas line can pull in enough air (or moisture) that could cause my generator to not run properly, yet still pass all of the tests per above? Should we go to the trouble of breaking the line loose from the meter and generator and pressure testing it like we did when we 1st installed it?

Thanks,
Mike

 

[Slomoola]

he condition was (and remains) very similar to what a gas engine sounds like when you've rebuilt the carb and don't have the fuel mixture screw adjusted just right -sounds like it's trying to find a bit more fuel, aka "hunting", aka "surging"

Does it have a carb or fuel injected?

Gas pressure at the genset is still within specs 7 WC at rest and 6.5 WC at idle.

Wonder what it is at full engine load? I would test and measure this one. Remember full load. If it drops .5WC just at idle, full load must be starving for fuel. What is rated full load gas pressure?

Oh you are pulling gas from a house gas trunk line? You mentioned hot water tank. In that case, all gas equipment needs to be on at full burn while you measure for WC pressure at the genny.

 

[Sponsor]

 

[Fitter30]

Brand and all the numbers off gas regulator and its pipe size. Pix of the generac model tag to pull up a install manual.

 

[Breplum]

Here is a situation we have encountered multiple times.
Moisture in the natural gas delivered by the local utility can have moisture. Said moisture can accumulate and precipitate out creating a water near-blockage. To remedy, here are the steps. We set up a gas test set that has high pressure gauge (say 100 psi) and a schrader valve (like on a tire valve stem). at the other end, we have a lever handle ball valve open to atmosphere...fill to 100 psi, then let 'er rip (protect eyes) by opening the lever handle valve quickly. The relieved pressure will blast out the water from the negative pressure differential.
Of course, a long suction tube into the gas line is an option...if main line is level

 

[Reach4]

This does not address the actual question... but I got to thinking about removing potential water in a line with vacuum plus time. This does not address whether the existing gas lines would collapse under a hard vacuum.

Summary... Idea to use a vacuum pump to remove moisture may or may not be practical. This may have to run for a long time to draw out the water, but it should do a really good job.

Just an idea not based on experience.. I was thinking you could adapt a vacuum pump as used in air conditioning. This would not need things to be level. Add a vacuum gauge. If you can maintain a good enough vacuum, the water would boil off at ambient or underground temperature.

But how good a vacuum? I found https://www.engineeringtoolbox.com/water-evacuation-pressure-temperature-d_1686.html with an Online Water Boiling Point Calculator. I was surprised it took a harder vacuum than I expected. I think under 10 mm Hg or 13.3 millibar (mbar) or 10000 micron would be needed. I did find https://www.zoro.com/pro-set-vacuum-pump-60-cfm-12-hp-50-microns-vp6s/i/G0964387/ which seems to be able to draw a 50 micro vacuum, which is good if I did my numbers. https://www.harborfreight.com/25-cfm-vacuum-pump-61245.html says it draws down to 75 microns.

Conversion Table

Easily convert units of vacuum with this chart including Torr, mmHg, mtorr/microns, PSI-a, Bar, mbar, mbar/hPa, inH2o, KPA, Pa, inHg, ATM. Click here!

digivac.com

 

[Sylvan]

We used to install drip legs to catch any moisture, but the powers that be outlawed them as idiots would use them as a future connection and cause major problems

 

[Fitter30]

Page 24 shows a sediment trap factory installed just before a factory installed reg. Years ago piped a generator had to increase the natural gas pressure to 2 lbs with a gas pump then gas reg to low pressure. Gen was hunting had factory rep come out was something with the electronics causing it. Can't remember what it was but it was fixed.

https://cdn.shopify.com/s/files/1/1151/7156/files/Generac_Installation_5-5-23.pdf?v=1710943834

Type of reg they recommend
Generac's home standby generators use a demand-type fuel regulator. A demand regulator provides fuel as the engine demands it based on the engine's load. It does not adjust the fuel pressure being provided to it. Demand-type regulators are used on all Generac air and liquid-cooled home standby generators.

 

[Jeff H Young]

how could a gasline under pressure suck air in ?

 

[Fitter30]

This does not address the actual question... but I got to thinking about removing potential water in a line with vacuum plus time. This does not address whether the existing gas lines would collapse under a hard vacuum.

Summary... Idea to use a vacuum pump to remove moisture may or may not be practical. This may have to run for a long time to draw out the water, but it should do a really good job.

Just an idea not based on experience.. I was thinking you could adapt a vacuum pump as used in air conditioning. This would not need things to be level. Add a vacuum gauge. If you can maintain a good enough vacuum, the water would boil off at ambient or underground temperature.

But how good a vacuum? I found https://www.engineeringtoolbox.com/water-evacuation-pressure-temperature-d_1686.html with an Online Water Boiling Point Calculator. I was surprised it took a harder vacuum than I expected. I think under 10 mm Hg or 13.3 millibar (mbar) or 10000 micron would be needed. I did find https://www.zoro.com/pro-set-vacuum-pump-60-cfm-12-hp-50-microns-vp6s/i/G0964387/ which seems to be able to draw a 50 micro vacuum, which is good if I did my numbers. https://www.harborfreight.com/25-cfm-vacuum-pump-61245.html says it draws down to 75 microns.

Conversion Table

Easily convert units of vacuum with this chart including Torr, mmHg, mtorr/microns, PSI-a, Bar, mbar, mbar/hPa, inH2o, KPA, Pa, inHg, ATM. Click here!

digivac.com

Using a vacuum pump for ac work they can only be used with a cold trap. Vacuum pump can't handle all the water. They can handle some vapor but not in any volume. Cold trap is an apparatus that directs the flow of air going to a vacuum pump across a very cold surface. The idea is to condense any vapors, before they make their way into the vacuum-pump, that might otherwise degrade the pump oil or damage the vacuum system.
My opinion they need the factory service rep all companies have one or more.
They can talk with the factory engineers to help diagnose problems.

 

[John Gayewski]

Up the pressure from your meter to 2 psi or even 5. Then get a properly sized regulator for your house and the generator separately.