GPM VS. PSI FOR A GIVEN PIPE DIAMETER 4

[pencilgeek]

Let me start by saying I don't know anything about fluid mechanics. I need to know how many GPM I can push thru a 2" pipe at 100 PSI. Assuming a length of 10 ft. And what would be the velocity. Seems like it would be a simple calculation. Can someone give me a formula?

Thanks
Chuck

 

[Latexman]

There are a lot of references that have tables of almost exactly what you want. It's usually in psi/100 ft of pipe for water though. I know Crane's Technical Paper 410 and Cameron Hydraulic Data has it. There are others; you may even have it in one of your old books.

At 100 psi for 10 ft, you are off the chart on the high velocity end. Erosion issues, noise issues, i.e. major problems would be in store for you.

To get in the ball park of normalcy, use 0.1 to 10 psi/100 ft. For 2" the corresponding flow range would be about 10 to 115 gpm.

Good luck,
Latexman

 

[25362]

GPM of what?

 

[pencilgeek]

GPM of water. And yes, the GPM should be high, in like the 200 GPM area. I have seen those books mentioned before in some google searches. Are those the "go to" books for calculations like this?

Chuck

 

[Latexman]

From Crane's TP410 website,

"Crane Technical Paper No. 410 (TP-410) is the quintessential guide to understanding the flow of fluid through valves, pipes and fittings, enabling you to select the correct equipment for your piping system.

Originally developed in 1942, the latest edition of Crane TP-410 has been fully updated to reflect the latest knowledge and research in the fluid handling industry. The TP-410 has served as an indispensable technical resource for over 60 years to specifying engineers, designers and engineering students."

I've used it almost 34 years. I recommend it highly. I wish I had had it when in school. And, it's not expensive, $60.



Good luck,
Latexman

 

[Latexman]

BTW, for 200 gpm, 2" is probably too small. Depending on what is being done and the quality/type of water, 3" (8.7 fps), 4" (5 fps), or 6" (2.2 fps) may be better choices.

Good luck,
Latexman

 

[bimr]

This question has been asked several times on this forum. Have you done a search?

http://www.eng-tips.com/viewthread.cfm?qid=276054

If you calculate the maximum velocity with Cranes, you will get a velocity around 20-25 ft/sec which equates to a flow of around 200-250 gpm.

Here is a link to a chart that supports this.

http://www.dakotasupplygroup.com/wp-content/uploads/2011/12/maxflow_chart.pdf

 

[ElSid1]

Ditto the Crane and Cameron. I tend to use the Cameron more. What is the application for?

At 100 psi for 10 ft, you are off the chart on the high velocity end. Erosion issues, noise issues, i.e. major problems would be in store for you.

.
You also have to deal with codes! For example, Civils frequently go into the 20-30 fps on water mains. As a mechanical, the plumbing code limits the velovity to 8 fps. I've had to explain to my civil counterpart why my branch line was bigger than his main. they were not impressed

 

[cvg]

civils DO NOT "frequently go into the 20-30 fps on water mains". This would be a very infrequent event, and probably only at a fire hydrant flowing at wide open. It is certainly not typical and municipal standards for water mains that I have seen are limited to 5 - 7 fps. where did you hear that and what kind of loons do you work with?

 

[pencilgeek]

You asked what the application is, and I probably should have mentioned it up front. But it is not civil or mechanical engineering. I am trying to figure out how much water I can push thru a plastic injection mold. Hence, the 10 ft. length. I am given water from a 2" hose at 100 psi and I am trying to figure out how many GPM I am being supplied. From this 2" hose it branches off into several smaller drilled lines and eventually back into a 2" return hose. I think there must be 100 calculations I have to do to figure this out, but I am just trying to get past the first step (input GPM). I appreciate all the help you guys are giving me, even though some of it does not apply. I did do a search on here for what I am looking for, but I don't think my terminology was close enough to find what I needed. I did see that another mold designer was looking for similar help in a similar situation, but that thread didn't help me much.

With my application in mind, which book would do me more good? Cameron or Crane? Just looking for an opinion if you have one.

Or, with my application in mind, is there a simple formula?

Thanks

 

[bimr]

The velocities in city water mains are always lower than the velocities in building water services.

 

[trashcanman]

Quote:

" I am given water from a 2" hose at 100 psi and I am trying to figure out how many GPM I am being supplied. From this 2" hose it branches off into several smaller drilled lines and eventually back into a 2" return hose."


This is a completely different problem than what first appeared in your 1st post. If I understand what you are describing, the water is to be forced through numerous small drilled lines and back to the return hose.
1. The water pipe IS NOT the bottleneck. The main pressure drop will be through the numerous orifices.
2. You do not have 100 psi to burn. There must be enough pressure available to return to the 2" return hose and back to the source.
3. Determine the pressure drop through the mold (psi vs. gpm. This must be done through field experiments). Leave enough return pressure so you will not cavitate your pump.

 

[cvg]

you cant get input gpm without output gpm. friction loss in the mold through all the drilled holes will reduce your pressure and flow rate. assuming this is a pump, then your pump curve also comes into play. a flow meter would be useful

 

[ElSid1]

cvg and bimr,
I was tasked with estimating water supply for a mid-rise, no FP, that was a differned tap. My calculations showed a 14" line, was able to "justify" a 12" in my estimates. The main was 12". I was told that the city water mains are allowed to go to higher velocities since they are buried (noise not an issue). I ended requesteing two 6" tap offs closer capacity to the 14", put the civil was not happy. What AWWA standard do the mains fall under?

 

[Latexman]

Trashcanman is right, completely different problem. Much more complex to solve theoretically. Is everything existing so you can experiment, or does this need to be figured out for a project?

Good luck,
Latexman

 

[cvg]

allowable flow velocity in city water mains is set by city standard, not AWWA. Every agency I have checked is 5 - 7 fps. Headloss at higher velocities have a large impact on capacity and pumping costs. Keep in mind that cities and water districts must deliver water at minimum pressures to the entire service area through literally miles and miles of water mains. Keeping velocity low and head loss low is essential to be able to do this. However, different standards apply to private service laterals which is what you are describing, not a water main.

 

[pencilgeek]

Thanks guys for being patient with me as I learn how to ask this question. I know how many GPM I need to push thru each mold (it varies depending on a few things), but I want to verify that I can actually push the required GPM thru the mold, at a given 100 PSI with a 2" supply hose. Am I jumping the gun trying to figure out how many GPM I am getting from the supply hose? Or do I need to look at the complete system first? Or do I just buy the book and improve my knowledge before I try to figure it out?

Chuck

 

[Latexman]

Am I jumping the gun trying to figure out how many GPM I am getting from the supply hose?

Yes.

do I need to look at the complete system first?

Yes.

do I just buy the book and improve my knowledge before I try to figure it out?

Yes.

You also may need to understand "manifolds", "distribution header", "maldistribution", "series flow resistance", and "parallel flow resistance", because it is more complex than either reference mentioned above gets into. You've also got a ways to go before you are ready to do this. It is not beyond you, IMO, but if time is critical and you have the budget, you may want to sub this out to an Engineering Firm.



Good luck,
Latexman

 

[77JQX]

If you want to low budget this and have the time to get some learning, EPANet is a free hydraulic simulator that can (probably) handle the hydraulic calculations for the complete system. As with anything else, if you don't understand the inputs, the results you get will probably be garbage. To get meaningful results, you'll need to educate yourself about friction factors, fittings, minor losses, what creates the souce water pressure, etc. But as far as calculating power, EPANet will match programs costing $1,000s.

 

[pencilgeek]

Latexman, thanks for the honesty. Time is not critical and I have never let not knowing how to do something keep me from trying. Question: Is this something I could learn to do if I took a class in fluid mechanics or does a person need degree? I am guessing that, since you recommend farming it out. that I would need a degree in fluid mechanics?

Chuck