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Old 10-05-2011, 06:05 PM   #1
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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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Old 10-05-2011, 06:23 PM   #2
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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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Old 10-05-2011, 08:14 PM   #3
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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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Old 10-05-2011, 08:27 PM   #4
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Quote:
Originally Posted by grandpa View Post
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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Old 10-05-2011, 08:50 PM   #5
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I'm not crazy about the tee with the plug in it on the outlet side of the gas meter.
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Old 10-05-2011, 09:04 PM   #6
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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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Old 10-05-2011, 09:05 PM   #7
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Quote:
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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Old 10-05-2011, 09:24 PM   #8
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Quote:
Originally Posted by Hack

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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Old 10-05-2011, 09:25 PM   #9
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Quote:
Originally Posted by Hack View Post
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
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Old 10-05-2011, 10:05 PM   #10
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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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