Pond Boss Forums INTRO Questions & Observations Fluid Dynamics question

O.K., it's late and I'm not having much luck getting my head wapped around flow rates, pressure losses, fps losses (velocity) in water pipes.

I'm trying to figure out what size pipe to run for a certain psi/gpm.

I used the Hazen-Williams Equasion, (using a C-factor of 150) but I'm coming up with the same fps (velocity) losses for the same size pipe and gpm rate, no matter what the length of run I plug in.

For instance: The length of run is 825', I want to make sure that it gets at least 70-75 gpm at the discharge end. (I'd really like to see 90 gpm at 15 psi) The auto fill valve is 1 1/2" I.D. and flows 90 gpm at 15 psi., 128 gpm at 35 psi., and 158 gpm at 55 psi. The auto fill valve will be placed at the discharge end of the pipe. What is the minimum size pipe that I can get away with for that length of run and still have the psi and fps within operating parameters for plastic pipe? Pipe will be the black poly, one piece, no sharp bends other than maybe one 90° bend where it leaves the well pump. I want to keep the fps at 5 or below.

That's because the Hazen-Williams gives you the head loss per 100 ft (see formula below). The result is independent of pipe length. You need to MULTIPLY the Hazen-Williams parameter by the foot length of pipe DIVIDED by 100 (825/100 = 8.25)

E.g.

f = 0.2083*(100/c)^1.852*q^1.852 / dh^4.8655

where

f = friction head loss in feet of water per 100 feet of pipe (fth20/100 ft pipe)

c = Hazen-Williams roughness constant (for PVC, use 150)

q = volume flow (gal/min)

dh = inside hydraulic diameter (inches)

E.g. for an 825' foot piece of 3" in. interior diameter PVC pipe, substituting all the relevant variables, you get the following:

Specific Head Loss (ft H2O / 100 ft pipe): 1.952

Specific Head Loss (psi / 100 ft pipe): 0.8

Actual Head Loss (1.952 * 8.25, ft H2O): 16.101

Actual Head Loss (0.8 * 8.25) (psi): 7

Velocity (ft/s): 4.09

So you would get a 16 ft H2O head loss, a 7 psi drop, and a 4.09 ft/s velocity drop for an 825' piece of 3" in. PVC pipe.

Bocomo:

Thanks. That's the same numbers that I got. Thinking about it today, why wouldn't the FPS depend on the length of run? Less friction loss would allow the water to move faster, right?

The FPS drop does indeed depend linearly on the length of run.

Hazen-Willams gives the head loss per unit length, just like miles per hour is distance per unit time. To calculate head loss, multiply the H-W by the length of pipe, just like you can calculate distance traveled by multiplying your average miles per hour by elapsed time. E.g. at 65 mph for two hours you'll travel 130 miles.

The mud is becoming clearer....

Sometimes I cheat

ETB

Does that calculate the velocity loss for the specific length of pipe or does it default to only 100' sections no matter what length is entered?

Why is the pipe under pressure? What is the use of the pipe?

You are not loosing any velocity because you are pumping X amount of water thru a fixed diameter pipe. Velocity will not change be it 100 feet or 825 feet. If you want 90 gpm, velocity will be the same thru the same diameter pipe. That's how flow meters work.

You mentioned 90gpm at 825 feet as your output.

Yes, it calculates head loss and all that for the specific length you enter. It also gives it based on 100 ft.

Might want to thumb thru other formulas to get info on other things you may need.

ETB stuff is pretty quick and reliable. Can't use it on projects I work on tho, except for estimating.

All pipes are under positive pressure if you are "pushing" liquid thru them. The pressure the pump has to handle (output) is based on all the factors of the plumbing after the outlet side of the pump. You also have to deal with the inlet side of the pump. A well pump would be submerged in water so It wont have to "lift" the water, as in suction.

The use of the pipe is to get water from point "A" to point "B".

I don't know much about esshup's particular situation, but I would look into gravity to get 90gpm @ 825' to the pond. The pump would be a whole lot smaller. 4-6" PVC vented to atmosphere every so often would do the trick. But then again, I don't know much about what he is dealing with.

Unfortunately, gravity isn't my friend in this situation, at least not much of a friend. The land is pretty flat.....

Trying to figure out the most economical way to run water to a couple of ponds from one centrally located well. Enough water to keep the ponds full during times of little rain. It doesn't help any that the ponds are dug in sand, and fluctuate with the ground water levels.....

Water still moves on a flat surface Scot. Just spill some on your kitchen floor and see. LOL And water moves to where ever there is an opening such as an overflow on a pond. Of course you know all that.

You can get gravity flow over a flat surface to move even better if you start it at a higher point. Hence why my well is at the highest point of my property although my buried pipes are fairly flat.

I would use gravity if at all possible. It's free and the government hasn't figured out how to tax it yet!

I use gravity to move water from and to all my ponds. Works like a charm.

After getting a quote from a directional boring company, it might be cheaper to put a well at each pond and direct bury electric.

Curious sre you running thru rock as to the need for directional boring?
I know I have one Siphon system out of 4' PVC to move water from one pond to just above another that moves close to the GPM your are talking about.

No, no rock, sandy soil. BUT, there's 100's of mature Oak, Maple, Hickory and Aspen trees in the way - no way possible to dig a trench without killing a lot of trees. Can't run it above ground either because of the below freezing temps in the winter.

I understand about working to keep the trees. I laid 600' of 1.5" thru trees with a big rider ditch witch borrowed from the local cable company. Digging the trench thru roots for it was easy and it did not kill any of the trees. However we did have to remove several smaller trees to snake our way thru while leaving the larger trees unharmed. One year later you could not hardly tell we had been thru if you did not know. The only problem was it made it look so good and cleaner in that area that my wife wanted me to thin out some more of the smaller trees LOL.

You can push electric a lot further than pushing water, cheaper. Maybe plan "B". ?

I was supposed to get a phone call back from another well driller but didn't. I've had my mechanics hat on the past 2 days, and now I'll probably have to wear it part of tomorrow too. But, that won't pervent me from making more phone calls.

I ordered a CD from Grundfos yesterday. Supposed to have all kind's of fancy stuff on it about wells, pumps, plumbing, energy efficiency. Supposed to have some fancy ciphering too! First, we'll see if I even get it.

EDIT: Oh well, scrap that idea. Got an email back today saying they were all out till next year.