lyndaval – posted 14 January 2002 07:51
Last season we put in a trial sprinkler system, using flexible hosing on top of the grass to establish location of the sprinkler heads. Now that we are ready to make this permanent, we need advice.
What diameter plastic pipe is recommended? I have been told 1/2″ to 1″. Which? Our yard has a slight slope that makes it difficult for the water pressure to run the sprinkler head at the higher point away from the faucet.
I am open to all advice. Thanks.
seed – posted 14 January 2002 10:03
lyndaval, you touched a subject that is dear to my heart.
The short answer is, “the bigger the pipe,” the better. But there are some other problems in using water from the house.
Large pipe size will not impede the flow, but will keep friction loss to a minimum, and will sustain the highest possible pressure at the sprinkler heads, and equal throughout. Plus, it takes no more work to dig a ditch for a 1″ pipe than for a 1/2″ pipe.
The one big problem is that since you are using municipal treated water which probably comes in to and through your house in maybe 3/4″ pipe, you are going to be greatly restricted how much water you can supply at any time. The general rule is to not make the water travel more than 5 feet per second, certainly not more than 7.5 feet per second. What happens when water travels at higher velocity is that it gets into turbulent flow, and can cause water hammer, cavitation, make a lot of noise, and maybe break the pipes. Since I don’t know the size or material (iron, PVC, etc.) of the pipe supplying the water, I can’t look up the value. But I would guess that you’re going to be down to 10 gallons per minute. So depending on what kind of sprinkler heads you use, you may possibly not be able to use more than a few heads per zone. As an example, a standard full-circle spray head with 30 degree trajectory operating at the lowest pressure of 15 pounds per square inch will supply 2.6 gallons per minute. Which says (dividing the 2.6 into the 10), you can only put 4 heads or so on a zone which would run at any time. Also, you would have to reduce the pressure at the source, which you can do by partially closing a valve, or even adding a pressure regulating valve.
Based on a system flow of 10 gallons per minute, 1/2″ PVC pipe is way too small, and you will have excess friction losses, resulting in a few pounds difference in pressure among different heads, depending on how they are arranged. The 3/4″ PVC pipe size would be theoretically minimally adequate to supply 10 gallons per minute, with a velocity of only 4.74 feet per second, and a friction loss of 4.30 pounds per square inch for every 100 feet of pipe run. I realize that you’re going to have way more than 15 pounds per square inch at the source, maybe 80, so 4.3 psi loss seems insignificant. But what is important is balance, so you don’t have higher pressure one place than another, or so a zone that’s 100 feet away gets the same pressure as one that’s 20 feet away. Plus you may want some flexibility should you ever get a well (if that’s possible in your area). Plus maybe your source of water is on a larger feed, maybe 1″ and not 3/4″, and your total reasonable supply is maybe 14 gallons per minute. Then you’re going to need 1″ distribution lines anyway. At least. Some would suggest that you work off a mainline of 1.5″.
So to finish this tortured story, it all depends on the source. Don’t make the distribution lines any smaller than the source, in your case 1″ seems about right.
Also, since you are already seeing some problems getting adequate water pressure up a slight slope, I suspect that your biggest problem may be that you are trying to get too much water (too large zones with too many heads) from an inadequate source.
Phil
[This message has been edited by seed (edited 14 January 2002).]
joe spano – posted 18 January 2002 16:43
i have put in a few systems myselffirst i went a pipe supply and gave them thelayout of the yard and i did a bucket teston my city supplied water(basicly tapped into my source and time how many gal per minute) they made up a plan abd i bought the mat. from them. but if u think u have the layout done already try the bucket test( do not use your garden hose spout on your house for this test tap into the water source and test it there) i believe i was getting some where around 20 gals per min so i would only put 5 three galmin heads per zone giving some slack for peak usage timei started with a pattern of five on a dice . .
.
. .
it work fine and then changed as the yard dictated remember every spot on the lawn should be covered by atleast two headshead to head coveragelook at this site for some re-inforcement of my statementshttp://floridaturf.com/staugust/water.htm
i have 15 yrs exper in turf carein pasco cty fla
joe spanojsspano@yahoo.com
Dave-Cypress Creek – posted 26 January 2002 08:53
If you want an in-depth tutorial that guides you in designing a home irrigation system, look at the following site:http://www.irrigationtutorials.com/index.htm#Sprinkler
badboy – posted 25 February 2002 19:33
I, NOT ONLY INSTALL AND SERVICE IRRIGATION SYSTEMS. I’AM A FIREMAN. IN SPRINKLERS AND FIRE THE MAIN WATER SUPPLY IS EITHER ALL THE WAY ON OR ALL THE WAY OFF.[NEVER HALF WAY] USING CITY WATER SUPPLY NOY ONLY IS SIZE OF SUPPLY,BUT HOW LARGE OF A COMMUNITY SOURCE IS COMING FROM[100 HOMES ON A GRID COMPARED TO 50]TIMES OF DAY OR EVENING YOU PLAN TO WATER.CITY PRESSURE IS GREATER BETWEEN THE HOURS OF 9:00p.m&6:00a.m in most neighborhoods.THIS HOPEFULLY GIVES YOU A LITTLE MORE HELP IN DESIGNING YOUR SYSTEM