Calculating gpm

mikim · Oct 24, 2001

thanks -- guess we wuz typing at the same time--
mike

john4nh · Oct 24, 2001

Yes, we wuz!!

$110 for the class..

Chillimau · Oct 24, 2001

Boy, this post has just turned to @#%!! Just kidding

Mikim, That engineering question is loaded with variables (problems to solve), whew!

John4NH, the ETA I was talking about is like what Bird described.

A lagoon is a square pond about 5' deep by 25' x 25' to 50' x 50' ( at the bottom) depending on daily flows and evaporation rates. Has a 3' run to 1' rise from the bottom to the top of the 2' berm surrounding the pond. So you have a total of 7' of depth, but about a three to five working area. Still has a septic tank to perform the anerobic action and uses wind and aglae for the aerobic action in the lagoon. They are somewhat common around my area. Have never smelled one stinking. Projected to have a fifty year life span. I think these are the cheapest system avail in my area. And is what the DEQ guy recommends. About less than 2,500 and only maintainence is to mow around lagoon and pump the septic tank as needed. ( suggested yearly).

Chillimau · Oct 24, 2001

Oh yeah, I could do a ETA or Lagoon myself and DEQ will come inspect. Septic tank $600-$800 plus some pvc. Maybe I could justify a bigger tractor and a backhoe with water line, electric line, septic system, basement and footings to do? I really need a bigger tractor for other things, so just need to justify the hoe... Sounds better all the time.

Bird · Oct 24, 2001

pump the septic tank as needed. ( suggested yearly)

Pumping out the septic tanks is another topic./w3tcompact/icons/wink.gif Several years ago I was doing a gas leakage survey in Sayre, PA, and read an article in the local newspaper that I found interesting. The city had extended their sewer lines into an area that had apparently been recently annexed into the city and wanted the residents out there to abandon their septic systems and connect to the new sewer line (at the residents' expense of course) and they ran into some rather vocal opposition because of the cost to tie into the city sewer. I don't know the end result, but the city wanted to agree to let them continue using their septic systems, but with an ordinance to require them to have the tanks pumped at least every two years if they did that.

When I had my aerobic system installed, I thought I'd just have it pumped every two years to make sure I never had a problem. My service company said, "Fine, if you want to waste the money, but we'll tell you when it needs pumping." So . . ., they told me; a week ago today, and I had it done; just under 4.5 years, and they said it shouldn't have needed it that soon, but they suspect my wife of using too much bleach in the laundry./w3tcompact/icons/frown.gif

Bird

TWINKLE_TOES · Oct 24, 2001

Gary.

AH I think I just found it. 

I think you did to Gary, good job. You will be a Fluid Dynamicist by dark, next thing ya know you'll be asking about Reynolds numbers./w3tcompact/icons/smile.gif
2.31 ft/psi is a pretty good number.
Al

RobertN · Oct 24, 2001

For structure work, figure 100gpm minimum on a single nozzle, at a minimum 100psi. For wild land, figure starting with a variable flow nozzle set at 35-40gpm at first, and then adjust for fire conditions, and figure about 100psi. I would conservatively say MAYBE two wild land nozzles on that one line.

I would check with your local fire dept. they can give you more details on particulars for your area.

If you could really flow 100gpm though, that would be pretty good! Not only could it allow you to put serious water down, it would also allow some good refill capability for a fire engine.

Remember though, before you try to fight fire, there's safety equipment and training too...

RobertN in Shingle Springs Calif

Chillimau · Oct 25, 2001

RobertN, thanks for the numbers. Once I figure out the flow I will research more. I didn't realize the amount of water pressure needed. I thought 100 gpm would be plenty. If I can get 100 GPM, I think it will be around 45-50 psi. Still too early to tell.

Al,... boy you made me do my homework! You lost me on that last number. But I have been researching the Reynolds number. Determines type of flow, laminate Re < 2300 or turbulent Re > 3400 (I think) or transitional if in between the two. If flow is laminate, a lot more friction is present do to the shear forces. If I kept all the terms in the right measurements I came up with around 680.

Re = pipe dia (l) x velocity (v) x fluid density (p)/fluid viscosity

l = sch 40 3" pvc = 3.042"
v= 4.40 to 4.70 fps ( I tried a couple formulas and got different results)
p= 62.41lb/cubic ft @ 50 degrees Fah
n = 1.308 @ 50 degrees Fah

So flow is laminar, correct, maybe...

Time for Darcy coefficient of friction, f=64/Re and the

Darcy formula = density x f x length x velocity squared/2 x diameter......???????

So will the darcy formula give a better indication of the anticipated flow?

I know I jumped ahead of the teacher!... and am probably on the wrong track.

TWINKLE_TOES · Oct 25, 2001

Posted by Chillimau (Bronze Member)
Posted on 10/24/01 08:18 PM

8:18 PM What time does it get dark at your place? I think I got it "Fluid Dynamicist by dark"

Gary, the 2.31 ft/psi is found by dividing a square foot of area (144 sq inches) by the density of water (62.4 lbs/Cubic foot)

In your case a head loss of 39.8 ft is a pressure loss of 39.8/2.31 or ~ 17 psia.

Al

Edited by twinkle_toes on 10/25/01 02:24 PM (server time).

JATO_RaT · Oct 25, 2001

Hey Bird, forgot I added to this post. I did not realize he wasn't irrigating. I irrigate with over 100 Rainbirds (not at one time) I don't have a meter. I'm on a well but I don't irrigate with well water. Here in the fruit basket capital we have irrigation canals. I order 3 miners inches of water from April 15th to October 15th. A miners inch is just over 11 gpm. I'm also on a party line. At any one time with no one irrigating, we have about 140 gpm at 120 psi available. No pumps are required, its all gravity fed. California is littered with all sorts of water projects especially with the Sierra Nevadas to the East and Cascades to the North. Between the Sierras and the Cascades, you won't find higher snowfall totals anywhere in the US. The snow makes a great reservoir. Rat...

Bird · Oct 25, 2001

OK, Rat, you're talkin' plumb outa my league when you talk about miners inches (which I never heard of) and 120 psi in a canal (how'd they do that?). And I'm old enough to remember party lines if you're talkin' 'bout telephones./w3tcompact/icons/laugh.gif

Bird

Chillimau · Oct 25, 2001

Al, that was 11:18 Oklahoma time. Dark got here about 7:20. 6:20 next week (boo) I got absorbed with this water problem.

OKAY! Gotcha on the 2.31ft. You just derived the number. I looked it up in a chart and multiplied the inverse of that, .4329 to get the psi number.

Thank you sir!

Safe to say I can get 100gpm at about 45-50 psi?

Chillimau · Oct 26, 2001

One more thought. What schedule pipe to use. Already talked with the water co., they don't care what schedule and don't even want to inspect the installation after the meter.

At 100 gpm, I figure a surge pressure of about 88 psi. Combined with the the line pressure of say 70 psi, comes to roughly 160 psi.

What schedule of pipe to use? Sch 40 has a 260 psi working press., SDR21 has a working pressure of 200 psi and SDR 26 has a working pressure of 160 psi. I think burst is three times working pressure.

I think SDR 21 @ 200 psi would be the choice. Would have a about a 40 psi fudge factor.

JATO_RaT · Oct 26, 2001

Bird, water is brought from the Sierras via canals. At some point they enter into a piping system. This is where they begin to "capture" the pressure. They keep these canals up on the ridges of the mountains and hills. The beauty is that if they started containing the pressure to early or high up, pressure problems would be enormous. Where I am, I have about 120 PSI so the water is being piped at about 230' above me. I'm at about 900' elevation. The only down side to irrigating this way is that we all need to use filters. At various times of the year, we may need to blow out our filters every other day. It also restricts irrigating to impact or Rainbird type sprinklers since they can easily pass the small debris that gets through the filter(s) Rat...

StanInCalif · Oct 26, 2001

I wouldn't go less than Sch. 40.

stan

Chillimau · Oct 26, 2001

Why?

I agree it is probably the most common schedule installed, but it costs more too. I will do sch 40 if necessary, just don't see the need yet. I don't think the compression force of the the ground or vehicles driving over it is going to crush even the 160psi pipe when it is buried 2'.

Meeting Code issues? Haven't looked at that yet

Would you lay it in a layer of sand or the native clay soil? I would like to use the O-ring pipe to avoid adding expansion joints.

StanInCalif · Oct 26, 2001

Chillimau-
I don't like the lighter stuff because it's more susceptible to physical damage and water hammer. I would put it sand to protect it from sharp rocks. I'm not familiar with the O-ring pipe you mentioned, but I've never layed a line as long as you're talking about, either. It would be best to see what your local code requires.

stan

JATO_RaT · Oct 26, 2001

First of all finding, 2" with o rings will be next to impossible. 2. What expansion, your worried about nothing. 2' in the ground, worry aout a truck driving over it? All this is for not, if you like the lighter stuff fine, use it and get greater flow because of the larger interior diameter. It will take the PSI. The hammer you speak of results in a quick acting valve, use gates instead of ball valves. Expansion, unless you have exceptionally variable water temps, don't worry. If you are concerned, don't trench perfectly straight and add some jogs. Sch 40 is nice because it will resist physical abuse both while in transit to you, while you stick it in the ground and from some rocks. Water/air hammer can disinigrate even SCH 80 pipe. When you glue it (forget about the o ring idea) prime it and use grey glue, its is the heavy bodied stuff that won't dry as fast but is the best for any voids. It is the only glue that you can use on 8" and up pipe. The primer etches the top few hundreths of an inch of PVC making it soft and getting the best cohesion/fusion between the mating surfaces. Now, go trench, glue as much of the pipe above ground, let it dry, throw it in the trench, cover it up.

P.S. Put a tee in every now and then, its easier now then later, Rat...

Bird · Oct 26, 2001

Rat, when he said using the o-rings, I assumed (maybe wrongfully so) that he was talking about the same kind of pipe that's usually used by the water companies around here. One end is flared much like other PVC, but has a rubber seal in it. You lubricate the small end of the next section and simply slide it into the flared one; no glue or solvent used. In this clay, the soil contraction and expansion with the dry and wet cycles causes lots of leaks, but using that type pipe virtually eliminates them because every joint is an expansion joint. And apparently it isn't hard to find. The only ones I've actually watched being installed was a 8" main for approximately 12 miles, and a 2" main less than a half mile long for a small development. Definitely looks to me like the best way to go.

Bird

Chillimau · Oct 26, 2001

Rat, I agree, I'm probably over thinking this, but problems are easy to fix right now. Good idea about the tee's.

As far as valves, I don't think I have ever seen a gate valve down in the dirt with the meter, always a ball valve. (not that I've seen many installations)

Bird, You got it. I like the o-ring pipe for the reasons you mention. Our clay can get 1" wide cracks during the summer. And I can get o-ring from 2" and up.