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# Pipe Sizing

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• #273652
MasterPlumbers
Keymaster

I am currently looking for info on pipe sizing. If anyone could help with online info I would be very
grateful.

Cheers,
Vitch.

• #288228

Vitch: A simple and easy to remember rule of thumb regarding water piping is: By doubleing the pipe size, four times the volume is possible at the same pressure.
Example: If 15 gallons per minute
is flowing through 1/2″ diameter piping system, 60 gallons per minute would flow through the same piping system if it were 1″ in diameter at the same pressure.
Akmed.

• #288229

But since you have quadrupled the volume, but only doubled the pipe circumference, friction loss will be less therefore the flow will be greater than four times. As a rule of thumb, we figure that a four inch pipe will deliver about the same as five two inch lines at the same pressure.

• #288230

Akmed, YOU are 100% correct.
Unfortunately an apprentice doesn’t get to learn pipe sizing until their 5th year of schooling (hopefully).

The 1st 4 years are just BASIC tools and how to learn to read a ruler and possibly some very basic code and cleaning fittings for the mechanic and carrying tools and unloading trucks delivering materials.

One Master plumber did lose his license for allowing an apprentice to go out alone and wow what trouble this kid caused just doing a simple toilet stoppage.

Knowing that “helpers” do have trouble with basic pipe sizing and do not know about Pi (3.14159265) R sq. length divided by 231 if in inches and multiplied by 7.48 if in feet.

So to KEEP IT SIMPLE (for) STUPID I use the KISS system when dealing with the schleppers in my shop.

So we use D D 6 and this works out the same as we honestly dont want to discourage helpers from tying to learn the very basics.

For example One 2″ pipe will equal the same AREA as four 1″ pipes

1 1 6 = 6 2 2 6 = 24 24 divided by 6 = 4 TA DUM

I have no idea where the 5th pipe came from SO lets try it another way huh?

3.1416 R sq 1″ pipe = .7854

2″ pipe R sq 3.1416 .1416

3.1416 divided by .7854 = 4 FOUR

no place do we find FIVE pipes

Only in a criminal mind do they arbitrarily look into the sky searching for a number.

Under NORMAL job conditions we would be conserative and figure 3 pipes NEVER more then the actual FU demand as we do take not only hydrostatic pressures and friction losses BUT the “Force” to over come the weight of water (in high rise buildings especially)

When a Journeyman plumber is asked to size a buildings water supply most will actually OVER size the piping one comerical size then actually required to allow for future fixture demands . For example if the piping demands are for a 21/2 ” supply we may go to 3″ on the origional install.

NEVER say 4 is good lets figure 5 then a 3rd year apprentice would come along and say HEY LETS make it 7 pipes equil the same volume.

Volume in pipe sizing is not 2 + 2 = 5 it doesnt work that way.

Here this may help http://www.masterplumbers.com/plumbing/plumbviews/1999/watersupply.html

• #288231

In the real world you will find that the WaterBoard will have a lot to say about pipe sizes into a building. It is well to remember that a larger pipe size will result in less friction regardless of existing mains pipe sizes.
( just a note )

• #288232

“Unfortunately an apprentice doesn’t get to learn pipe sizing until their 5th year of schooling (hopefully).

The 1st 4 years are just BASIC tools and how to learn to read a ruler and possibly some very basic code and cleaning fittings for the mechanic and carrying tools and unloading trucks delivering materials.”
Your kidding ??? 5 year apprenticeship in the US, and for the first 4 years he/she is nothing but cheap labour ?? By fourth year they shoud be able to work unassisted on most types of jobs, not just be able to tell if the tradesman has a tape or a hammer in his hands

• #288233

Let’s keep it real simple. You have to run a 1000 foot 4″ pipe, but there are two beams in the way. There is only 3/8″ between them. Using the example above, which disregards laminar flow resistance, 1,000 1/8″ pipes 1,000 feet long will supply the same amount of water. I don’t think so unless you only need a few gallons an hour. In fact about that time you would welcome the virtual fifth pipe you get by reducing the resistance area in relation to the volume and flow.

• #288234

You should look up look up friction loss/100ft. Four 2in. pipes will not give you the equivalent of a 4in. pipe. You have to consider the gpm. For ex. a 100 foot run of 2in. @ 200gpm will net a pressure loss of approximately 25# in each of the 2in. pipes. A 4in. pipe will net a pressure loss of 1# in the line, this is due to the boundary friction, water that is in contact with the pipe. figures used here are for smooth pipe(copper). These are taken from the standard plumbing code.