# Gas lines



## voltatab (Jan 2, 2010)

Ok, this was asked, and attempted to be explained to me before, but I'm asking again cause I still haven't quite gotten it. 

In the pics below. We have a gas line that comes from the street, in 3/4" pipe. It goes through the diaphragm, then into the meter. In the 2nd pic the outlet come off meter, in 3/4, than as it 90s into the wall, a reducer used backwards to increase pipe size is used to increase the pipe to 1 1/2"pipe

What I still don't fully understand Is the difference between ;
why you can do this with a gas line but not water? 
Also why are 90s not factored into running a gas line, as far as a sizing chart goes? 
How come this is not creating a "bottle neck" effect? It would certainly do so with water... 
I always thought that i cant run larger pipe off of a smaller gas line that has already been reduced in pressure and been through the meter... But i see this quite a bit 
Enlighten me please!


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## Mississippiplum (Sep 30, 2011)

It has to do with pressure, pressure is higher before reg and a volume of gas can pushed through a smaller dia pipe after reg pressure is lower so a larger dia pipe has to be used to keep the volume of gas at a reasonable amount. This is how I learned it was.


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## grandpa (Jul 13, 2008)

The "diaphragm" is the pressure reducer. Once it is reduced, you need a larger pipe to carry the btu/

You can always increase the size of a water pipe. It is done often in yard sprinkler work, to reduce losses in long runs.

A few elbows does not significantly change the capacity equation, and whether it is gas or water, I don't see this as causing a bottleneck


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## Mississippiplum (Sep 30, 2011)

grandpa said:


> The "diaphragm" is the pressure reducer. Once it is reduced, you need a larger pipe to carry the btu/
> 
> You can always increase the size of a water pipe. It is done often in yard sprinkler work, to reduce losses in long runs.
> 
> A few elbows does not significantly change the capacity equation, and whether it is gas or water, I don't see this as causing a bottleneck


 
when i did sprinkler work we did that quite often


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## Tommy plumber (Feb 19, 2010)

I'm not crazy about the tee with the plug in it on the outlet side of the gas meter.


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## user4 (Jun 12, 2008)

Tommy plumber said:


> I'm not crazy about the tee with the plug in it on the outlet side of the gas meter.


It doesn't like you either.


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## Hack (Oct 2, 2011)

> It has to do with pressure, pressure is higher before reg and a volume of gas can pushed through a smaller dia pipe after reg pressure is lower so a larger dia pipe has to be used to keep the volume of gas at a reasonable amount. This is how I learned it was.


everyone has always told me this... but every other plumber i know argues the fact that no matter how big you increase the pipe size you are still restricted to however much the feed pipe can put out. for instance if you have 3/4 feed coming off the meter and bushign it up to 1 1/2 your only gonna get as much as that 3/4 feed will push so you dont reallly do yourself any good unless the outlet on the regulator is 1 1/2... same with water... on water you will lose a bit due to frictional drag but for most yard lines that are less than say 100 ft you wont notice a difference... ive been dealing with fluid dynamics for quite some time. still everyone argues with me dunno why lol


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## Plumberman (Jul 7, 2008)

Hack said:


> everyone has always told me this... but every other plumber i know argues the fact that no matter how big you increase the pipe size you are still restricted to however much the feed pipe can put out. for instance if you have 3/4 feed coming off the meter and bushign it up to 1 1/2 your only gonna get as much as that 3/4 feed will push so you dont reallly do yourself any good unless the outlet on the regulator is 1 1/2... same with water... on water you will lose a bit due to frictional drag but for most yard lines that are less than say 100 ft you wont notice a difference... ive been dealing with fluid dynamics for quite some time. still everyone argues with me dunno why lol


They lied to you...

Once the high pressure side of a meter is regulated to ounces, the larger pipe diameter carries the volume needed to carry the BTU loads to burn all the appliances. 

You take that same 3/4" gas line through a regulator to reduce pressure and carry that same 3/4" line into the house/building then attach that same line to multiple appliances with a high number of BTUs you will starve to main, because the line isn't sized to carry it...


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## Mississippiplum (Sep 30, 2011)

Hack said:


> everyone has always told me this... but every other plumber i know argues the fact that no matter how big you increase the pipe size you are still restricted to however much the feed pipe can put out. for instance if you have 3/4 feed coming off the meter and bushign it up to 1 1/2 your only gonna get as much as that 3/4 feed will push so you dont reallly do yourself any good unless the outlet on the regulator is 1 1/2... same with water... on water you will lose a bit due to frictional drag but for most yard lines that are less than say 100 ft you wont notice a difference... ive been dealing with fluid dynamics for quite some time. still everyone argues with me dunno why lol


pressure plays a big role in flow also, when the pressure is reduced on a 3/4 inch line putting out say 10 gpm, if that 3/4 is continued flow will rapidly decrease dependent on how much the pressure is reduced pressure and flow are proportinal, now upsize that 3/4 to say 1 1/4 and the flow will not decrease except what is lost to normal friction loss. we are not increasing flow or pressure we just preventing it from decreasing, say we have a 1 inch pipe putting out 15 gpm the static pressure is 50 psi, we crack a 1in bv the more we crack it the lower the pressure will drop, say we have 1 1/4 same flow same pressure the same results will accur. but if we reduce the pressure we need to up the pipe size to make up for that pressure thats pushing the liquid or gas that we just lost, if we keep the same pipe size flow will rapidly drop off, so we upsize the pipe and all is good:thumbup:


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## voltatab (Jan 2, 2010)

Wow, I can't seem to grasp this concept...

So in theory I could then have a 1/4" outlet pipe connected to a 2" line and it still works ok? Even after gas pressure has been reduced? Indent see how a bottleneck affect doesn't happen. How can the amount of gas thats being carried through a 2" gas line also pass through a 3/4" section of the same run and not slow down the volume or speed? I mean, if i connect a fire hose to a 1/2" hose bob, it's not going to operate like a fire hose ( I realize that's not a great example but that's kinda the thought in my head)
Then if I'm in need of a 3/4" gas line for something (say a BBQ) but only have a 1/2" feed, why can't I just throw a 3/4"X1/2" reducer on it and trust that it will now supply properly? 

Also Your saying that a 1/2" feed to feed sprinklers will deliver the same amount of water as a 3/4 " feed would? I just don't see it. And 90s do play a roll in restriction in water I've been told, just not enough of make a huge difference that anyone notices. Yet I've been told gas does not. Again what the heck

I keep rereading these posts, trying to get it. I think it might have to gradually sink in...


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## Tommy plumber (Feb 19, 2010)

If gas line is increased in pipe size, the volume is increased, not the pressure. The increased volume is what the appliances need to function properly. 

Think of this: if a gas leak occurs in a room and the room fills up with gas, what happens when someone enters the room and lights a match? Kaboom! But the gas was not under any pressure in the room. But there was a large volume of gas in the room.

Also, less pressure is needed with gas, as opposed to water because gas is much lighter than water; so less pressure is needed to 'push' the gas through the pipes to buildings. Miles of underground pipes filled with natural gas weigh alot less than miles of pipes filled with water.


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## TX MECH PLUMBER (May 27, 2011)

The larger pipe is basically a large storage tank..It carries the volume you need to match your BTU plain and simple.


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## voltatab (Jan 2, 2010)

Ok I'm getting that part now...but what happens then when the room or storage tank is emptied IE the appliance uses all the gas in the pipe and is demanding more? The original outlet won't have enough size to refill the large pipe in time, no? 

Like cracking the gas valve open just a bit, eventually the pipes will fill with gas, but when you crank on the furnace, you'd get a good flame at first, than a small little flame coming out until I open that baby up! Right?


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## Plumber patt (Jan 26, 2011)

water and natural gas have different densities. the pressure likely comes in at 60 psi or so. and gets regulated down to 1/4 - 1/2 psi to supply the house. So you can definetly upsize the piping to whatever you need provided the length of run and supply btu are met.


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## Plumber patt (Jan 26, 2011)

voltatab said:


> Ok I'm getting that part now...but what happens then when the room or storage tank is emptied IE the appliance uses all the gas in the pipe and is demanding more? The original outlet won't have enough size to refill the large pipe in time, no?
> 
> Like cracking the gas valve open just a bit, eventually the pipes will fill with gas, but when you crank on the furnace, you'd get a good flame at first, than a small little flame coming out until I open that baby up! Right?


when you size your gas piping, you size it for the amount of pressure (7 inches w.c) with the maximum allowable pressure drop of 0.5 inches w.c. every appliance has a pressure drop on the system, but you are sizing the piping to accomodate for it.


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## U666A (Dec 11, 2010)

Tommy plumber said:


> If gas line is increased in pipe size, the volume is increased, not the pressure. The increased volume is what the appliances need to function properly.
> 
> Think of this: if a gas leak occurs in a room and the room fills up with gas, what happens when someone enters the room and lights a match? Kaboom! But the gas was not under any pressure in the room. But there was a large volume of gas in the room.
> 
> Also, less pressure is needed with gas, as opposed to water because gas is much lighter than water; so less pressure is needed to 'push' the gas through the pipes to buildings. Miles of underground pipes filled with natural gas weigh alot less than miles of pipes filled with water.





TX MECH PLUMBER said:


> The larger pipe is basically a large storage tank..It carries the volume you need to match your BTU plain and simple.


Excellent! NG vs. Liquid is like apples vs. Oranges.

Its a volume game...


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## TX MECH PLUMBER (May 27, 2011)

voltatab said:


> Ok I'm getting that part now...but what happens then when the room or storage tank is emptied IE the appliance uses all the gas in the pipe and is demanding more? The original outlet won't have enough size to refill the large pipe in time, no?
> 
> Like cracking the gas valve open just a bit, eventually the pipes will fill with gas, but when you crank on the furnace, you'd get a good flame at first, than a small little flame coming out until I open that baby up! Right?


Low pressure gas is measured in W.C. (Water column). And yes when an appliance fires you will have a drop in pressure witch is residual pressure but there is a rang of pressure on the appliances that they will operate at... When ther is a loss of pressure the regulator will let a higher volume of gas through but the same pressure


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## Michaelcookplum (May 1, 2011)

Plumberman said:


> They lied to you...
> 
> Once the high pressure side of a meter is regulated to ounces, the larger pipe diameter carries the volume needed to carry the BTU loads to burn all the appliances.
> 
> You take that same 3/4" gas line through a regulator to reduce pressure and carry that same 3/4" line into the house/building then attach that same line to multiple appliances with a high number of BTUs you will starve to main, because the line isn't sized to carry it...


Correct, it's all about volume and pressure


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## easttexasplumb (Oct 13, 2010)

The gas company should have meter couplings to go from the meter to any size pipe.


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## Plumberman (Jul 7, 2008)

If you want to truly make your head spin..

Yahoo Search- pv=nRT


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## Titan Plumbing (Oct 8, 2009)

Plumberman said:


> If you want to truly make your head spin..
> 
> Yahoo Search- pv=nRT


Why did you do that to me tonight? Why?


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## Plumberman (Jul 7, 2008)

Titan Plumbing said:


> Why did you do that to me tonight? Why?


Lol

Man I've been studying that for a while. Figured someone else ought to feel the love.


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## TX MECH PLUMBER (May 27, 2011)

Plumberman said:


> If you want to truly make your head spin..
> 
> Yahoo Search- pv=nRT


Aa that's elementary stuff I learned that in my first year!!! No really now I feel stupid!!! Lol


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## Plumberman (Jul 7, 2008)

TX MECH PLUMBER said:


> Aa that's elementary stuff I learned that in my first year!!! No really now I feel stupid!!! Lol


It's applicable in what we do with piping sizes, once you dig thru all of the different theories of it.


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## TX MECH PLUMBER (May 27, 2011)

Plumberman said:


> It's applicable in what we do with piping sizes, once you dig thru all of the different theories of it.


O I agree,,, it's just trying to comprehend the info in that form.. I'm more of a hands on learner... Or at least have formulas and equations explained!!!


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## Plumberman (Jul 7, 2008)

I just hope I didn't throw the OP for a loop.

If I did it wasn't my intention.


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## U666A (Dec 11, 2010)

Plumberman said:


> I just hope I didn't throw the OP for a loop.
> 
> If I did it wasn't my intention.


I do believe that Voltatab has officially gone
cross-eyed...

:laughing:


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## Plumberman (Jul 7, 2008)

U666A said:


> I do believe that Voltatab has officially gone
> cross-eyed...
> 
> :laughing:


I figured I would open Pandoras Box for him on ideal gas law... 

If nothing else it definitely proves that water and gas don't act the same...


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## Dun' Right (Sep 27, 2010)

Ok, this is a little off subject, but I had to share. 

A few years back we did a church down in kansas city. The project took 7 years (seriously) from start to completion. They were slow to pay (years slow....) and the prices in 7 years were dramatically different than bid price from the beginning. 

Anyways, for whatever reason the price to cut into the street, tap into the water main, tap fees, permit fees, equipment, labor, materials, the whole sha-bam, was about $15k. After 7 years that price was all of the sudden twice that much. 

Don't ask me why the water wasn't put in first, I didn't start the job. There were at least 3 other company's that were at this place, didn't get paid, and left. (dream job right?)

Anyways, the job was an add-on, and the add-on was about 3 times as big as the orig. church. Add on had 2" water lines feeding the upstairs and downstairs restroom's. 

Everything was flushometer, toilets and urinals. They even had showers, locker rooms, and the preacher had his own little personal bathroom retreat. 

The orig. building had 3/4 line coming in. The church decided that instead of spending 30k on a new 2" water tap, they would just feed the entire add-on off the old 3/4. The city approved it, and we tied it in. 

That being said, 3/4 water line feeding 100 gallon heater, (guesstimate) 15 toilets, and 5 urinals. Plus the other cafeteria, locker rooms, preacher/handicap bathrooms. 

You could flush 4-5 toilets at the same time and not notice a big difference in pressure or volume (from the toilets). 

Always blew my mind. The volume in the 2" lines was enough to feed the supply I guess.


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## TX MECH PLUMBER (May 27, 2011)

Dun' Right said:


> Ok, this is a little off subject, but I had to share.
> 
> A few years back we did a church down in kansas city. The project took 7 years (seriously) from start to completion. They were slow to pay (years slow....) and the prices in 7 years were dramatically different than bid price from the beginning.
> 
> ...


There wasn't a large storage tank???


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## Dun' Right (Sep 27, 2010)

TX MECH PLUMBER said:


> There wasn't a large storage tank???


Nope, direct feed.


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## BROOKLYN\PLUMB (May 21, 2010)

Dun' Right said:


> Ok, this is a little off subject, but I had to share.
> 
> A few years back we did a church down in kansas city. The project took 7 years (seriously) from start to completion. They were slow to pay (years slow....) and the prices in 7 years were dramatically different than bid price from the beginning.
> 
> ...


Because that ain't alot of gpm, and could have all been fed of the 3/4" line (4-5 toilets)


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## HOMER (Jun 5, 2011)

Tommy plumber said:


> I'm not crazy about the tee with the plug in it on the outlet side of the gas meter.


Required by the gas company...Service tee.
allows Gas Co to change meter or regulator without interupting gas service.
they will feed it temporarily through the tee(using a rubber bladder bag and a probe fitting)
tee plug to hand tight,bladder bag over tee,bypass gas on, purge air,spin tee off through bladder bag,insert probe,probe cuts gas off to middle port of tee,cut off gas to meter,make repairs , restore
otherwise they have to enter the premises,check appliances,purge air and relight pilots

In Cali, we must modify the meter sets to install EQ valves(on the outlet side of meter)
Gas company not pleased to see the tee gone(or placed in an unusable positon)
code requires EQ valve size to match largest pipe size at meter set..
even though the majority of the piping is ¾"..in that picture from 1st post it would require an 1½" EQ valve(and bracing bar secured to wall)


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## Plumberdrummer (Oct 3, 2011)

Not so sure if this will help but heres a couple of things to consider.We always size the piping for the load.This includes the elbows, and the material of the pipe determines the friction loss. If the load is calculated properly the PIPE will be the right size. By using the bell designed reducing coupling to increase you have probably effected the flow as little as possible. All of these points are calcuable using flow formulas.If your work is correct then the flow should be acceptable. These calculations take into account specific gravity of the gas and distance. I believe that if your work is correct then any shortcomings would be delt with by the utility.


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## 1703 (Jul 21, 2009)

Ever notice on a gas sizing chart how, using 3/4 as an example, the btu load on 10' is way greater than 100'?

it's the same thing in your picture. Maybe the overall load is such that 1.5" is needed because of distance.

As to 90's not factored in when sizing- they should be. Ever see the phrase _equivalent feet? _


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## voltatab (Jan 2, 2010)

I DO notice that on a chart! Good example. Not that I would do this but basically would I be able to have for example 10' of 3/4 on a 2" run anywhere I want as long as I dont go above the 3/4 length load? (or less than the load of my appliances?) 

I actually have not seen 90 equivalents before on a gas sizing chart except on one. If factoring 90s into a total length of run is important, then why are there so many charts wo them?

Also, any thoughts on the 2009 IFGC & commentary book? I think it might do me well


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## Mississippiplum (Sep 30, 2011)

Dun' Right said:


> Ok, this is a little off subject, but I had to share.
> 
> A few years back we did a church down in kansas city. The project took 7 years (seriously) from start to completion. They were slow to pay (years slow....) and the prices in 7 years were dramatically different than bid price from the beginning.
> 
> ...


Was the 3/4 tapped into close to the meter? Because if it was then the 3/4 had sufficient flow, and then Running a 2in service line prevented a drop in flow, also what was the static pressure, higher the static higher the flow through that 3/4.


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## Dun' Right (Sep 27, 2010)

Mississippiplum said:


> Was the 3/4 tapped into close to the meter? Because if it was then the 3/4 had sufficient flow, and then Running a 2in service line prevented a drop in flow, also what was the static pressure, higher the static higher the flow through that 3/4.



I don't really remember. Too many jobs ago. I just remember I thought it was nuts.


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