i set it with the burners off. if you have a volume problem and set it while running you may exceed the maximum allowable inlet pressure of the valve when it stops.

 

Either way is fine, however, you need to check the gas pressure both ON and OFF. Both values provide great information. The values listed in the manufacturers IOM are for pipe sizing ONLY!

Low Pressure gas valves are rated with a 1" W.C. drop across the valve. If your valve is rated at 150,000 btuh and you are using it on a 75,000 btuh unit, then the valve should be able to provide 75,000 btuh with a line pressure of 0.5" W.C. above manifold pressure (sorta...it isn't straight line but you get the point.)

 

what does proper gas pressure prove with burners off.... zero in my opinion.....

 

It proves that the regulator will limit the pressure to its setting. If the inlet pressure goes higher when the gas valve is closed, it's time to replace the regulator.

 

If it calls for 5" to 14" it is what the gas valve needs to open and close properly. I always set in the middle with burners off. Too much pressure and the valve could have problems opening or regulating.

 

I was just wondering how other Techs adjust the pressure on gas regulators, do you do it with the burner on or off? Say a unit calls for a inlet gas pressure of 5" to 14" w.c., does that mean with the burner firing or not. I use to do it with the burners off, but several years ago I found it was better to adjust the gas pressure with the burner on. I was just curious what other guys do.

it means you must have no more than 14" wc static (burner off) and more than 5"wc working (burner on) pressure. proper piping practice will yield no more than .5" pressure drop on a 7" system and no more than 1 psi drop on a 2lb system between burner on and off. this the most recent code. before allowable pressure drop was 1" and 1.5 psi.

note the above was for natural gas

 

it means you must have no more than 14" wc static (burner off) and more than 5"wc working (burner on) pressure.

ch4man, that's a good explanation of the inlet rating. It is good to see all of the replies to my post, thanks everyone for doing so. Even though I like to adjust a regulator with the burner on, I also check it with the burner off to make sure the pressure doesn't go above the max rating.

 

Ditto Ch4man but would add: the gas piping for any building must be sized for full load. That means every appliance should be delivered the full load all at once. There are certain gas appliances that may perform fine when just that one appliance is firing but suffer from delayed ignition, sooting, flashback and poor combustion if the inlet pressure is below spec. Most gas combination valves for HVAC operate with a manifold pressure on NG of 3.5 wci. These valves usually have about a 1-1.5 wci pressure drop from the inlet vestibule to the outlet. So, if you add 3.5 + 1.5= 5.0 wci min. inlet pressure. While the target pressure drop is 0.5 wci, this yields a margin for safety of 2.0- 0.5 = 1.5 wci margin. Some streets may have 7.0 wci supplied pressure without a pressure regulator at the meter. The danger here is that during peak demand periods, the inlet pressure certainly can bottom out. Many older neighborhoods in the East are like this. If there is a regulator at the meter, you will probably have sufficient gas at the meter as long as the piping was properly sized to the load.

 

set it running & check it off.You can have a reg creep up when off causing lockups or damage to the gas valve.Also we don't live in a perfect world where everyone before us did decent work.
I have a few places set around 12" off with a 7" or less while running due to undersized piping the owner will not replace.
Normally I shoot for 8" on a standard unit.

 

I didn't read everything here, but I generally deal with multiple gas appliances in kitchens. I learned to check both - static & operating pressures.

With most all gas equipment, static pressure (everything OFF) shouldn't exceed the 1/2 psi (about 14"WC) rated input pressure of most line regulators and combination valves. Anything more coming in needs a higher rated regulator to knock inlet pressure down to 1/2 psi or less.

In kitchens, there's multiple appliances, so I then check "dynamic" pressures - with everything calling for heat. In other words, all gas appliances running simultaneously to ensure all receive their specified pressures. I at least want minimum rated pressures for open burners on stoves and in ovens. They're fairly general in their operation. More critical equipment such as air-induced infrared burners need to remain within a tight of window of operating pressure. So, if the equipment needs 3"WC per the data plate, then THAT it must be throughout all possible demands on the kitchen line's possible gas demands.

So...with natural gas - I prefer 7'WC into whatever regulating device that's feeding the appliance DURING OPERATION. Then - AT and NO LESS THAN the data plate's specified pressure read at the burner manifold during operation, as read from the equipment's own regulating device.

 

As hearthman said, there are MANY places around here that have a low pressure service.

PECO Gas has some neighborhoods that receive 5.5" at the meter. The entire neighborhood (as in dozens and dozens of homes and businesses) relies on a small building with gas equipment inside to supply this pressure to every site. With old piping, this sometimes does not happen. The 5.5" is what the gas Co refers to a "tariff limit," meaning that the price the a charging those customers is based on that pressure, so they don't like to go above it.

I like to see 7 or 8" going into a gas valve, but as you can see, that isn't always possible.

Now, since it's Saturday, let's have a smile.

I was sent on a no heat call in a store down on Walnut St in Philly. It's kind of an upscale shopping district with 2-phase service and converters that date back 70 or 80 years.

The second floor had a Trane rooftop unit with some older, weathered gas piping going to it. The unit is nine years old, and the store has been open for three years.

I test the unit, and I find the control board is not sending voltage to the gas valve. Inducer runs, good spark, but the gas valve gets nothing. It's all controlled by one board, so we order a board.

I return, install the new board, and test. Nada.

I don't smell gas, so I start to trace gas piping to see if the meter has been pinned. It's something I have found before, when someone in the corporate office misplaces a gas bill or two.

Here is what I found.

 

As hearthman said, there are MANY places around here that have a low pressure service.

PECO Gas has some neighborhoods that receive 5.5" at the meter. The entire neighborhood (as in dozens and dozens of homes and businesses) relies on a small building with gas equipment inside to supply this pressure to every site. With old piping, this sometimes does not happen. The 5.5" is what the gas Co refers to a "tariff limit," meaning that the price the a charging those customers is based on that pressure, so they don't like to go above it.

I like to see 7 or 8" going into a gas valve, but as you can see, that isn't always possible.

Now, since it's Saturday, let's have a smile.

I was sent on a no heat call in a store down on Walnut St in Philly. It's kind of an upscale shopping district with 2-phase service and converters that date back 70 or 80 years.

The second floor had a Trane rooftop unit with some older, weathered gas piping going to it. The unit is nine years old, and the store has been open for three years.

I test the unit, and I find the control board is not sending voltage to the gas valve. Inducer runs, good spark, but the gas valve gets nothing. It's all controlled by one board, so we order a board.

I return, install the new board, and test. Nada.

I don't smell gas, so I start to trace gas piping to see if the meter has been pinned. It's something I have found before, when someone in the corporate office misplaces a gas bill or two.

Here is what I found.






View attachment 456361

My taxes from 1993?

Galvinized pipe flaking off and plugging somthing downstream?

Thats a good place for a drip leg too.

 

You have to set regulators with flow. That's what the do is regulate flow. When the flow stops , they lock up and cease to flow.

 

Nope. You do not have the privilege to advertise on this site.

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