Reply To: Pipe size vs. flow rate. vs. pressure drop chart wanted (water)

In reply to message posted by kook:
What???? 140 gallons/minute??? That sounds REALLY high.. How about when you add-in the normal length of 3/4″ copper pipe run through the house – there’s a good 50′ run before the 3/4″ tee’s out into some 1/2″ for faucets, spinkler, etc…

Now your getting the picture HUH? :-)

You asked for a ball park number something out of LEFT FIELD

We did not take friction losses into account (BJ will explain that) We did not consider pressure drops or what other fittings are being used and fixture requirements inside the structure

What we did do is take 50 PSI and a given pipe size and plugged in the numbers as given.

I didn’t bother to even try to locate the books as this is basic math for sizing piping

Later when it is really critical we plug in all the factors needed.

If you would like ILL sign you up to my list and you can ask the really professional guy/gals on there lots of hydraulic questions.

You see there are a whole bunch of BJ’s out there who do not comprehend how complex a plumbing system can be.

They kind of get confused with facts relating to most fields.

To him piping systems are one size fits all like trailer park plummin.

You gave too little information to give you a fine tuned answer.

What I did was take the pressure you said and figured on the low side 50 PSI flowing through a given sized pipe 1.5 inches would give you about 138 GPM

To find the GPM I had to first find the velocity .BJ will explain how this is done when only pressure is given.

Once we know the velocity and we already know the size of the pipe we just calculate the GPM

For a 3/4 dia pipe with 50 PSI would give you a flow around 34.5 GPM

A 1 ” pipe would give you a flow about 61.25 Gallons Per Minute.

Now you can understand why we need to know the actual materials and actual developed length and what are the actual Fixture demands and what probability factor are we using for fixture flow?

Are we going to use 40% of the fixtures or 75%?

Is there a peek demand like a Movie theater when intermission everyone runs to use the facilities. HECK of a pressure drop

Is this piping going to supply any fire suppression piping systems?

What is the actual lowest pressure you can expect? What is the peek pressure you may see on this system?

See how now your already ahead of the so called plumbers out there?

NOW you can fully appreciate home centers even more as the majority of the home owners can do a much better job at installations then the average stumblebum now dabbling in the trades.

The person with intelligence asks the right questions and finds the answers unlike the lame who can only criticize.

Have a very happy and healthy New Year and please feel free to E mail me.

As far as I am concerned this post is closed Feel free to E mail me if you have any questions.


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