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Eastern Pennsylvania

I am having trouble understanding how do deal with the difference in pressure down a length of hose. Say you have 1/2" to 3/4" tubing with 4 sprinklers coming off of it, one every 12 feet or so. The sprinklers would be connected to the main tubing by 1/4 inch tubing. How do you deal with the first sprinkler having way more output than the 4th sprinkler? It seems unpractical to put a valve on each sprinkler. Am I missing something? Thanks, -Jim

12/30/2008 12:57:19 PM

Ctpumpkin@optonline.net

Depends on the starting pressure, length of run, total gradient change, the number of fittings, etc. I used to install residential sprinklers. I'll never understand why folks think that reducing the pipe diameter will increase pressure

12/30/2008 2:52:11 PM

Eastern Pennsylvania

I know people are using sprinklers to water their patches, and obviously more than 1 sprinkler is needed for most sized patches. So what are the methods for getting even distribution of water over the patch? Just an idea of the basic methods would be appreciated. Thanks!

12/30/2008 4:48:10 PM

For my overhead I like geardrive "even coverage" sprinklers mounted 6' high, with tweeking, I cover 70'x100' area with 3 heads, run your main supply to the center and tee to the ends for even pressure and delivery. Simple and cheap to install.
3/4" hose to the center, 5/8" hose drops to the outside heads, outside set to 180° with the center head running at 360° and overlapping the side arches,,play around when installing and then use gauges set at different places in the patch to make sure the coverage is even. Always check the moisture level at the root zone to make sure it is what you want.

When the plants are small adjust those heads for the needed "throw".

All that said, I like to hand water whenever possible ;-)

12/30/2008 5:04:07 PM

Eugene, OR

In most irrigation systems, pipe is sized to maintain an acceptable velocity, usually 5 ft/s or less for PVC. When considering a system with a number of sprinklers, the pipe closer to the source must be larger as the flow rate is higher there than at the end of the line. Because the flow rate through a pipe is equal to the velocity of flow times the cross sectional flow area, the pipe diameter must increase as you get closer to the source to keep the velocity at a safe level.

As for pressure, a good approximation is that the average pressure in the pipe is equal to the pressure at the distal sprinkler plus 25% of the friction loss in the pipe. Pressure losses due to friction also drastically increase as velocity increases so pipe diameter is often adjusted to reduce friction losses as necessary.

I can post some basic rules on figuring pressure loss in a pipe if you want.

12/30/2008 7:38:07 PM

Eastern Pennsylvania

Dan, are you using a product like this: http://www.amazon.com/Nelson-Drive-Sprinkler-Control-1204/dp/B0009NES2Y

If so, my questions are if you reduce the flow, does the coverage stay even, and how are you mounting the sprinklers at 6'?

Thanks!

1/6/2009 3:51:27 PM

I use Rain Bird, not sure of exact model# and they are buried in the snow right now ;-)

Here's a link to one online source (I buy at a local box store)
http://www.lawnh2o.com/rainbird/rainbird_gear_drives.htm

Mount on pvc whatever length you want, fittings to make the connection at the same "box store" use a t-stake for the support.

The heads have a slider adjustment for distance(as the plant grows) I don't try to adjust flow, it does take some playing around to get the patch covered, then check for dry spots and hand water as needed. Hard to explain at the keyboard somethimes.

1/6/2009 5:20:05 PM

South Bloomfield, Ohio

I haven't used it for many years and haven't even done a search on it, but Bernoulli's Equation comes to mind when calculating pressure and flow(I think I spelled it correctly). And Steve is right, there must be some known values here.

1/6/2009 7:39:21 PM