# Calculation Question



## Phat Cat (Apr 1, 2009)

How many GPM would come out of a 1/2" pipe under 50 PSI?

I'm looking for the answer and also the formula to calculate the answer.

Thanks in advance.


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## OldSchool (Jan 30, 2010)

It should be close to 5 GPM .... we usually used a five gallon pail back int he day to see what we got in one minute.... the city main here was always close to 5 GPM


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## jc60618 (Jan 24, 2010)

PlumbCrazy said:


> How many GPM would come out of a 1/2" pipe under 50 PSI?
> 
> I'm looking for the answer and also the formula to calculate the answer.
> 
> Thanks in advance.


 
I could be wrong but I think you also need to figure out the velocity ft/sec of the water. The formula that I was taught gives you the GPM but does not take into account the PSI.

Diameter square X L (velocity of wate ft/sec) X .0034= Gallons per second


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## OldSchool (Jan 30, 2010)

here is a chart that may help you

http://www.tpub.com/content/construction/14259/css/14259_50.htm


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## SlickRick (Sep 3, 2009)

How long is the pipe?


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## Phat Cat (Apr 1, 2009)

OldSchool said:


> here is a chart that may help you
> 
> http://www.tpub.com/content/construction/14259/css/14259_50.htm


Excuse my ignorance here, but why would the length of the pipe be important? I understand friction loss (a little, make that very little). I'm looking for a general answer.

In our newsletter I want to explain how much water one could expect if a pipe completely blew apart.


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## SlickRick (Sep 3, 2009)

PlumbCrazy said:


> Excuse my ignorance here, but why would the length of the pipe be important? I understand friction loss (a little, make that very little). I'm
> 
> The friction loss makes a dramatic difference when it comes to gpm. I was using a flow calculator. At 25' it came up 28 gpm. @ 200'- 3.5 gpm.


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## Phat Cat (Apr 1, 2009)

slickrick said:


> PlumbCrazy said:
> 
> 
> > Excuse my ignorance here, but why would the length of the pipe be important? I understand friction loss (a little, make that very little). I'm
> ...


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## OldSchool (Jan 30, 2010)

i dont think there is a general answer to be found....the chart starts at source pressure and not end pressure.... You also have to realize that the pressure on a closed system will remain the same until the pipe burst and while it was free flowing the pressure would drop.

You should run a simple experiment using a 5 gallon bucket and see how long it takes to fill it up from your laundry tub or outside hose.


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## SlickRick (Sep 3, 2009)

There really is no general answer to that one,


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## stillaround (Mar 11, 2009)

We used to say 11 gal/min for 1/2" and 18 gal/min for 3/4....43gpm for 1"


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## OldSchool (Jan 30, 2010)

I think you would be safe to say in your news letter anywhere from 14 GPM to 5 GPM or go in the middle 9.5 GPM

You see it all depends on were the break is in the house and the overall restriction in the lines


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## Phat Cat (Apr 1, 2009)

I will give a range, best case/worst case. 

Along with the caveat that it depends on what their pressure is, where the break is, number of fittings etc.


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## OldSchool (Jan 30, 2010)

Plumb

Just for the fun of it do the bucket thing and let us know what you get


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## Phat Cat (Apr 1, 2009)

OldSchool said:


> Plumb
> 
> Just for the fun of it do the bucket thing and let us know what you get


I'll do it this weekend and report back. :yes:


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## SlickRick (Sep 3, 2009)

You might as well make something up. Without the variables, it is just a made up figure.

Dazzle them with brilliance, or baffle them with bologna.


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## OldSchool (Jan 30, 2010)

I am on a well here so it wouldn't be the same as your results or I would have given it a try:yes:


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## TheMaster (Jun 12, 2009)

OldSchool said:


> I am on a well here so it wouldn't be the same as your results or I would have given it a try:yes:


What does being on a well have to do with it? 50psi is 50 psi I dont care if its a well or city water.


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## pauliplumber (Feb 9, 2009)

PlumbCrazy said:


> I will give a range, best case/worst case.
> 
> Along with the caveat that it depends on what their pressure is, where the break is, number of fittings etc.


Take the highest number and say "You could lose up to"


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## grandpa (Jul 13, 2008)

Not an easy question for a bunch of plumbers! An engineer would be all over it with his slide rule in a heartbeat. Real world, we do have to consider the distance, because the given 50 PSI is at the source...let's say 50 PSI constant at the service entrance to the house. A broken pipe will allow more flow than standard design would allow. ( 5 to 7 gpm is nominal for 1/2 " pipe). SO, there will be pressure drop in the system. And there is some long length of pipe where the flow would be a trickle because the pressure loss is so great. It is a differential equation, because as the flow slows down, the loss then decreases....etc.etc.

For an approximation, you could run a bath spout wide open, time how long to fill a 5 gallon bucket. That would at least start to get you into the ball park.


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## PLUMBER_BILL (Oct 23, 2009)

PlumbCrazy said:


> How many GPM would come out of a 1/2" pipe under 50 PSI?
> 
> I'm looking for the answer and also the formula to calculate the answer.
> 
> Thanks in advance.


Try This ....
http://www.engineersedge.com/fluid_flow/pressure_drop/pressure_drop.htm


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## OldSchool (Jan 30, 2010)

TheMaster said:


> What does being on a well have to do with it? 50psi is 50 psi I dont care if its a well or city water.


 
Seeing my pump can not supply 50 PSI dead start and that as soon as I would start running water my pressure would drop.

So give your head a shake :laughing: are you really a plumber


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## Cal (Jun 17, 2008)

A LOT ,,, that is a freakin mess when a 1/2" line breaks and runs for a minute .

yep , that's my equation = A LOT !! 

Did i help ??


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## Protech (Sep 22, 2008)

Not enough data to answer the question. Need to know the length of the pipe as well as the type of pipe. You will also need to know how many fittings and which types. You will also need to know the temperature of the water......We ARE talking about water right....and not some other fluid??



PlumbCrazy said:


> How many GPM would come out of a 1/2" pipe under 50 PSI?
> 
> I'm looking for the answer and also the formula to calculate the answer.
> 
> Thanks in advance.


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## breid1903 (Feb 8, 2009)

*$400.00+*

overnight loss in rochester, about 15 20 years ago when the biker that lived in lower apt smashed cpvc off under kitchen sink. pushed broken pipe down into crawl space. water a good 3" deep, dirt floor. job payed very well. dip said he didn't know how it happened. barbell weigh still under sink. he got cute with me, i called the law and invited them in. drugs every where. they gave him a new home. lol. i pack. i got called for low or no water in rest of building. breid..................:rockon:


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## pdxplumber (Nov 21, 2009)

Tenant improvement in a strip mall about five years ago. Setting finish first thing in the morning. I ask the boss if the water is off. " of course it's off, it was off last night when we left, hurry up..." Cut the copper stub out to install the stop and WHAMMY!! Lots of water. How much comes out of a half inch line at 50 psi?
Enough to seriously **** up your day, thats all people need to know.
I didn't say anything to the boss, he felt bad enough about forgetting he had turned the water on.:laughing:


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## ZL700 (Dec 8, 2009)

With 50 PSI or 115 feet of head constant at the 1/2" unobstructed pipe opening the water would flow at 52.8 GPM.*

I actually have a chart for this from about 1/4" up to 3"? I can post when home from travel if anyone wishes to see/have it. 

I also could share the means of calculating flow from an open end pipe base on distance, open air space on top of flow if pipe isn't flowing fully, and arc.


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## OldSchool (Jan 30, 2010)

ZL700 said:


> With 50 PSI or 115 feet of head constant at the 1/2" unobstructed pipe opening the water would flow at 52.8 GPM.*
> 
> I actually have a chart for this from about 1/4" up to 3"? I can post when home from travel if anyone wishes to see/have it.
> 
> I also could share the means of calculating flow from an open end pipe base on distance, open air space on top of flow if pipe isn't flowing fully, and arc.


I would really like to see that chart.... the chart that I posted is way less than that :blink:


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## Protech (Sep 22, 2008)

How do you know which roughness coefficient to use?



ZL700 said:


> With 50 PSI or 115 feet of head constant at the 1/2" unobstructed pipe opening the water would flow at 52.8 GPM.*
> 
> I actually have a chart for this from about 1/4" up to 3"? I can post when home from travel if anyone wishes to see/have it.
> 
> I also could share the means of calculating flow from an open end pipe base on distance, open air space on top of flow if pipe isn't flowing fully, and arc.


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## ZL700 (Dec 8, 2009)

It's based on the pressure at the nozzle which in this case is the open pipe. Similar to straight stream tips in firefighting the pressure is known at the pump, the hoseline size, type and length is known, then the nozzle tip pressure can be read, thus flow rate is then calculated.

I used to teach pump operators course at the local VFD.

If you want to figure pipe friction, then tell me it starts at 50 psi, minus pipe & fittings, come up with a open pipe pressure less than 50 psi, such as 45 psi and again on 1/2" it would be 50.1 gpm


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## Tommy plumber (Feb 19, 2010)

Huh?


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## ZL700 (Dec 8, 2009)

Smaller Pipes


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## ZL700 (Dec 8, 2009)

Larger Pipes


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## ZL700 (Dec 8, 2009)

Open pipe flow measuring


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## Tommy plumber (Feb 19, 2010)

*Zl 700*

pretty cool info, thanks. :thumbsup:


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## piercekiltoff (Jul 22, 2009)

Another thing we do in the pump & well world is use orifice weirs to measure flow rate on large test pumping setups. You take a 10 to 12' length of pipe, 8" or so (depends on flow rate) and machine an 'orifice plate' to fit in the end. The orifice is sized to flow certain flow rates at specific pressures. A pressure measurement is then made using a tube & ball (for ft of water) prior to the orifice plate. You could use similar calculations with the theory being that the pipe and the orifice are infinitely close together in size (see the calculus equations in this article). Of course, it's been awhile since I've done calculus, so it might all break down as you get closer....

The weirs are used when you need to measure flow rate in 1/10ths or less per gallon and your pumping rate is 1000 to 2000 GPM or higher. It gets interesting.

Also, our rule is up to about 15 GPM from 1" pipe, 25 from 1-1/4, 35 from 1-1/2, and 2" is up to about 50. That does not take into account friction, and we generally work with a mean pressure of 50 # for fire flow & what not (though a lot of our clients are actually ending up with near 80 PSI for most of their daily usage). Of course, I don't work in smaller pipe sizes, so I don't know off the top of my head. I do know a 25 GPM orifice is about 3/8" across.


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## OldSchool (Jan 30, 2010)

ZL700 said:


> Smaller Pipes


seems really high ...the chart is for restriction on a larger GPM thats what giving you your 52 GPM


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## OldSchool (Jan 30, 2010)

Nozzle Discharge – Gallons per Minute (GPM)

1) Discharge Formulas
a. With Nozzle 
Discharge (GPM) = 30 X Diameter of Nozzle2 X ÖNozzle Pressure
*GPM = 30d2**ÖP*

Work Problem: How many GPMs are flowing through a 2 ½” hoseline with a
1 1/8” nozzle tip with a nozzle pressure of 50 psi?

GPM = 30d2ÖP
GPM = 30 (1.125)2 Ö50 (nozzle size converted into a decimal)
GPM = 30 (1.27) (7.07)
GPM = 269.37

b. Without Nozzle (open butt)
To find the discharge pressure of a hoseline without a nozzle, simply use 90% of the original discharge formula. The hose diameter will substitute as the nozzle size in this case.
GPM (open butt) = 90% X 30 X Hose Diameter2 X ÖPressure
*GPM (open butt) = 27d2 **ÖP*

*Velocity *


1) Formulas
For velocity, you will be given either the height of the water or the pressure. Therefore, two formulas for velocity will be discussed.
*a. *Velocity = 8 X ÖHeight of water or *V = 8**ÖH*
b. Velocity = 12.1 X ÖPressure of nozzle or *V = 12.1**ÖP*

Work Problems:
What is the velocity of water flow is the nozzle pressure is 60 psi?
V = 12.1 ÖP
V = 12.1 Ö60
V = 12.1 (7.75)
V = 93.78 fps

What is the velocity of water flow from a water tank 50 ft high?
V = 8 ÖH
V = 8 Ö50
V = 8 (7.07)
V = 56.56 fps

*Flow Velocities*


The velocity of water varies inversely with the cross section of the hoseline and nozzle tip. What does this mean?? 

With the same nozzle pressure:
Changing to a smaller nozzle tip will increase nozzle velocity / pressure
Changing to a larger nozzle tip will decrease nozzle velocity / pressure

The inverse relationship between velocity and nozzle size simply means that when one increases, the other decreases and vice versa.


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## grandpa (Jul 13, 2008)

I think the comparison to a pumper is not valid, because the fire engine can rev the pumps to maintain GPM.

Now, THIS is a fire truck!


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## ZL700 (Dec 8, 2009)

grandpa said:


> I think the comparison to a pumper is not valid, because the fire engine can rev the pumps to maintain GPM.
> 
> Now, THIS is a fire truck!


Perhaps, but to a point, 2 FF's can barely handle 100 PSI on a automatic nozzle, which means about 160 PSI at truck with 200' of 1-1/4" firehose


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## TheMaster (Jun 12, 2009)

I just connected a 1" prv set to 50psi to my hose faucet with a 50' hose in between. On the outlet side of the prv I reduced to 1/2 and then screwed a pex male adapter into it with a piece of 1/2 pex about 8' long. Its flowing at a rate of 9.75 gpm.


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## SlickRick (Sep 3, 2009)

TheMaster said:


> I just connected a 1" prv set to 50psi to my hose faucet with a 50' hose in between. On the outlet side of the prv I reduced to 1/2 and then screwed a pex male adapter into it with a piece of 1/2 pex about 8' long. Its flowing at a rate of 9.75 gpm.


Was that the 2-5 gal. buckets test? :laughing:


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## ILPlumber (Jun 17, 2008)

Is that a NY minute or an Alabama minute?

gpm= ghey pics / minute


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## TheMaster (Jun 12, 2009)

slickrick said:


> Was that the 2-5 gal. buckets test? :laughing:


It was a 5 gal test over 30 second time period.:thumbsup:


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## Phat Cat (Apr 1, 2009)

Matt said:


> Is that a NY minute or an Alabama minute?
> 
> gpm= ghey pics / minute


Tick tock, tick tock.

Time is running out. :thumbup:


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## Phat Cat (Apr 1, 2009)

I left the 5 gallon bucket at the shop, so I did it a different way.

I ran the water for a minute. Then I filled up a one gallon container in 12.97 seconds. So I came up with 5 GPM, give or take. Some water spilled out and there was a slight delay in stopping the stop watch.


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## ZL700 (Dec 8, 2009)

TheMaster said:


> I just connected a 1" prv set to 50psi to my hose faucet with a 50' hose in between. On the outlet side of the prv I reduced to 1/2 and then screwed a pex male adapter into it with a piece of 1/2 pex about 8' long. Its flowing at a rate of 9.75 gpm.


Whats the hose ID?

Rubber or vinyl?


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## OldSchool (Jan 30, 2010)

ZL700 said:


> With 50 PSI or 115 feet of head constant at the 1/2" unobstructed pipe opening the water would flow at 52.8 GPM.*
> 
> I actually have a chart for this from about 1/4" up to 3"? I can post when home from travel if anyone wishes to see/have it.
> 
> I also could share the means of calculating flow from an open end pipe base on distance, open air space on top of flow if pipe isn't flowing fully, and arc.


I guess you were way out on your 52.8 GPM


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## Protech (Sep 22, 2008)

Where are we measuring this 50 PSI at?


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## ILPlumber (Jun 17, 2008)

Protech said:


> Where are we measuring this 50 PSI at?


I think Z is measuring it at the source.


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## TheMaster (Jun 12, 2009)

ZL700 said:


> Whats the hose ID?
> 
> Rubber or vinyl?


The hose faucet is fed by about 20' of 1/2 soft copper. Then I connected a hose thats about 5/8 i.d. to it and its vinyl...it has a brass end on it too.


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## Protech (Sep 22, 2008)

50 gpm sounds way high. I would guess closer to 15-20gpm at 50 PSI flow-pressure at the start of the pipe run.



ZL700 said:


> It's based on the pressure at the nozzle which in this case is the open pipe. Similar to straight stream tips in firefighting the pressure is known at the pump, the hoseline size, type and length is known, then the nozzle tip pressure can be read, thus flow rate is then calculated.
> 
> I used to teach pump operators course at the local VFD.
> 
> If you want to figure pipe friction, then tell me it starts at 50 psi, minus pipe & fittings, come up with a open pipe pressure less than 50 psi, such as 45 psi and again on 1/2" it would be 50.1 gpm


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## RealLivePlumber (Jun 22, 2008)

Ain't no way you are filling a 55 gallon drum (almost) in one minute. 

I have 80 psi city water, 1"k copper service @ 100', and it takes me a minute to fill 5 gal.


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## ILPlumber (Jun 17, 2008)

Did ya get off on a decimal place Z?


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## OldSchool (Jan 30, 2010)

Z's chart is for a fire pumper truck with a nozzle at the end


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## Protech (Sep 22, 2008)

OK, I ran the numbers. Assuming a water temp of 5C and 100 feet of straight 1/2" I.D. pex pipe with no fittings with the pipe inlet pressure at 50 PSI the flow rate will be 2.94 gpm and the flow pressure at the end of the pipe will be 38.74 PSI with a velocity of 4.8 feet per second.

:thumbup:


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## TheMaster (Jun 12, 2009)

Protech said:


> OK, I ran the numbers. Assuming a water temp of 5C and 100 feet of straight 1/2" I.D. pex pipe with no fittings with the pipe inlet pressure at 50 PSI the flow rate will be 2.94 gpm and the flow pressure at the end of the pipe will be 38.74 PSI with a velocity of 4.8 feet per second.
> 
> :thumbup:


So you have 50psi to start with and when you allow full flow you only lose alittle over 11 psi?


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## Protech (Sep 22, 2008)

yes


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## TheMaster (Jun 12, 2009)

Protech said:


> yes


Then why are you getting under 3 gpm and I'm getting over 9 would 90' of pipe drop my volume by 6gpm?


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## Protech (Sep 22, 2008)

Dunno, maybe your water is wamer? I don't make the rules. That's just what the math shat out.........


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## TheMaster (Jun 12, 2009)

Protech said:


> Dunno, maybe your water is wamer? I don't make the rules. That's just what the math shat out.........


 My waters about 75-80 right now in the dead of summer. I dunno either I'm just tellin what the rig did and it was over 9 gpm.


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## Protech (Sep 22, 2008)

Raising the temp to 10C brings the flow rate up to 3.0099578gpm with a pressure loss of 11.2585546 PSI


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## Protech (Sep 22, 2008)

3.42gpm at 50C


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## Protech (Sep 22, 2008)

That's the problem. My calculation was for 100'.



TheMaster said:


> I just connected a 1" prv set to 50psi to my hose faucet with a 50' hose in between. On the outlet side of the prv I reduced to 1/2 and then screwed a pex male adapter into it with a piece of 1/2 pex about *8' long*. Its flowing at a rate of 9.75 gpm.


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## Protech (Sep 22, 2008)

At 8' I come up with 14.495gpm with 50C water.


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## Protech (Sep 22, 2008)

If I drop the temp down to 68F with that same 8' length of pipe, I get 13.24 gpm


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## TheMaster (Jun 12, 2009)

Ok my water temp is 87 degrees ..the pressure is set at 50 psi. 8' piece of 1/2 pex and I get 10 gpm. I checked the temp of the water before and after the test. I got almost a 5 gal bucket full in 30 seconds so I'm rounding up to 10gpm


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## Protech (Sep 22, 2008)

Seems like the math and the test are pretty close to one another. You did say you used a crimp pex fitting right? Maybe that's why your number is a bit lower. Try it again using a sharkbite adapter and remove the plastic insert that should put you closer to the theoretical number as the equations didn’t factor in any fittings.


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## Protech (Sep 22, 2008)

While I do appreciate your input, nozzles and pipes are 2 different things.



ZL700 said:


> Smaller Pipes


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## Bayside500 (May 16, 2009)

can someone explain to me why a few degrees of tempature would make any difference in the flow ?


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## Protech (Sep 22, 2008)

The viscosity of water (like most liquids) changes with temperature. Hot water is "thinner" than cold water. You can hear this when you open up a faucet on the hot side. Notice how the pitch changes as the cold water is purged away by the hot water. That change in pitch is due to the change in viscosity.

Just like the change in viscosity from air to helium makes your voice change pitch.



Bayside500 said:


> can someone explain to me why a few degrees of tempature would make any difference in the flow ?


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## Protech (Sep 22, 2008)

Get a 2 pieces of 1/2" pipe 1' long and fill them with molasses. Heat one of the pipes up and pour hot molasses in it while the other with cold. Blow thru both. Notice how the cold pipe/molasses is damn near impossible to blow thru while the hot one is easy. Water is the same way. 



Bayside500 said:


> can someone explain to me why a few degrees of tempature would make any difference in the flow ?


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## Tommy plumber (Feb 19, 2010)

Maybe ZL 700's charts were in liters per minute?? Cuz I know 50 gpm is high for a 1/2" line based on just my memory.:huh::huh:


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## ZL700 (Dec 8, 2009)

OldSchool said:


> Z's chart is for a fire pumper truck with a nozzle at the end


No its not, its a theory from ITT/Goulds pump

Hey I didnt publish it


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## ZL700 (Dec 8, 2009)

TheMaster said:


> I just connected a 1" prv set to 50psi to my hose faucet with a 50' hose in between. On the outlet side of the prv I reduced to 1/2 and then screwed a pex male adapter into it with a piece of 1/2 pex about 8' long. Its flowing at a rate of 9.75 gpm.


So it would be 50 PSI minus 20' of 1/2" copper loss + loss from from 50' 5/8" hose, fittings, valve, etc.

So its not 50 PSI at end of hose of course.


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## ZL700 (Dec 8, 2009)

Protech said:


> While I do appreciate your input, nozzles and pipes are 2 different things.


The end of a pipe could be the nozzle, thus the pressure is read at end not upstream


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## TheMaster (Jun 12, 2009)

ZL700 said:


> So it would be 50 PSI minus 20' of 1/2" copper loss + loss from from 50' 5/8" hose, fittings, valve, etc.
> 
> So its not 50 PSI at end of hose of course.


No.....I have about 75-80 psi at the hose faucet. From the hose faucet I attached a hose and at the end of the hose I attached a 1" prv set at 50psi. Out of the prv I installed a 1/2 mipx1/2" crimp with about 8' of pipe on it.


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## TheMaster (Jun 12, 2009)

Tommy plumber said:


> Maybe ZL 700's charts were in liters per minute?? Cuz I know 50 gpm is high for a 1/2" line based on just my memory.:huh::huh:


Common sense tells you a 1/2" pipe with 50 psi is NOT going to flow 50gpm.......thats just under a gallon per second:whistling2: His calculations are incorrect and its obvious.


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## ZL700 (Dec 8, 2009)

TheMaster said:


> Common sense tells you a 1/2" pipe with 50 psi is NOT going to flow 50gpm.......thats just under a gallon per second:whistling2: His calculations are incorrect and its obvious.


"his" you mean someone at ITT.

Hey I just looked at it fast but yes common sense tells us it's off a decimal or is GPH perhaps.


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## TheMaster (Jun 12, 2009)

ZL700 said:


> "his" you mean someone at ITT.
> 
> Hey I just looked at it fast but yes common sense tells us it's off a decimal or is GPH perhaps.


Whats ITT?


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## SlickRick (Sep 3, 2009)

Here you go TM.


http://www2.itt-tech.edu/cts/index.cfm?code=1286022


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## 6th Density (Nov 29, 2010)

Great thread guys!!
I've been reading through it and researching on it online. I was looking for an online calculator and stumbled across this little gold mine.
Sorry, if this has been posted already on another thread and is common knowledge.

Here it is (make sure you scroll down to the *Fluid Mechanics - Hydraulics - Flow Properties section)...

http://www.ajdesigner.com/

Cheers!!:thumbup:
edit: don't forget to check out page 2, 3, 4, and 5 "miscellaneous section" with more plumbing related calculators


*


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## 6th Density (Nov 29, 2010)

Update:

An even better calculator!!
Built by the man himself, Gil Carlson.

http://www.bellgossett.com/BG-SystemSyzer.asp
Click on the download for windows
Click on the agree terms
Download it.

Enjoy!!

You can order their handy "plastic wheel" also. Carlson made it back in the early 80's.

Here a picture of it and info about it.
http://www.fiainc.com/documents/12-09SystemSyzer.pdf


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