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07-01-2010, 11:00 AM   #16
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Quote:
 Originally Posted by Alan Really?
Yes, it doesn't matter if he puts in a 1" pipe or a 12" pipe, the pressure will be the same 80 psi. Pressure loss is a function of flow rates through specific pipe diameters and distances, so he might actually gain a fraction of a pound under residual flow because the friction loss through a 1" pipe is less than a 3/4" pipe under the same flow rate. His old choke point or bottleneck was where the pipe changes from 3/4" to 1/2", now that he's putting in a 1" pipe after the meter, his new choke point will be the 3/4" service line from the street when the sprinklers are on. Going larger pipe size increases residual pressure, but since his length of 1" pipe is short, the increase is minimal.

For example:
Using 80 psi static pressure as a starting point

10 gpm through a 50 foot 1/2" pipe will loose 44 psi, the pressure at the end of that run will be 36 psi.

10 gpm through a 50 foot 3/4" pipe will loose 6 psi, the pressure at the end of that run will be 74 psi.

10 gpm through a 50 foot 1" pipe will loose 1.5 psi, the pressure at the end of that run will be 78.5 psi.

That why you sometimes see larger pipe diameters inside the homes with street pressures in 40-50 psi range, they need to keep friction loss down to maintain 30 psi minimum at the fixtures. He has 80 psi static pressure, so thats why they put a 1/2" line to feed his entire house and he's not having problems with pressures when multiple fixtures are running, he has almost 50 psi of pressure available for friction loss.

 07-01-2010, 11:09 AM #17 Just call me Andrew   Join Date: Mar 2009 Location: Albany, NY Posts: 2,265 Rewards Points: 1,020 I'm having trouble understanding how pipe size, flow rate, and pressure relate. Your example shows 10gpm for all 3 pipe sizes. Wouldn't my GPM drastically increase? The 80PSI static pressure measurement i took was from a hose bib fed off 1/2" pipe in my house. __________________ Andrew
 07-01-2010, 12:52 PM #18 Member   Join Date: May 2010 Location: Massachusetts Posts: 133 Rewards Points: 75 I can't calculate friction loss with knowing the gpm, and I can't calulate gpm without knowing the friction loss. One of these has to be known in order to figure out the other. A 1" pipe and 80 psi is not enough info to figure out what residual pressure and flow rate you will see on your system. Every leg of your system will be different based on distances and pipe sizes as well. Think of it like a garden hose, if you don't have a sprayer on the end of the hose your going to get maximum flow with minimum pressure. If you hold up a hose flowing full steam, the pressure behind it is like a measly 5 psi. Once you attach a sprayer on the end of the hose, the pressure increases drastically because the sprayer acts as restrictor only allowing a certian flow rate through the sprayer increasing the pressure, and now your can shoot water 25 feet across the yard because the pressure ramps up once the flow ramps down. Since you have 80 psi, you WILL get higher flow rates since you have a higher pressure behind the water, but the pipe size and the distance also acts as a restrictor and water can only move so fast through a pipe. 15-20 feet per second is close to the highest velocity you'll see on any piping without a restriction before fittings start to fail.

 07-01-2010, 02:43 PM #19 Just call me Andrew   Join Date: Mar 2009 Location: Albany, NY Posts: 2,265 Rewards Points: 1,020 So using the garden hose example...if you reduce the pipe size, you increase pressure. Why isnt the revese true for my sprinkler? I increase from 3/4" to 1"...why doesn't pressure go down? __________________ Andrew
07-01-2010, 03:36 PM   #20
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Quote:
 Originally Posted by secutanudu So using the garden hose example...if you reduce the pipe size, you increase pressure. Why isnt the revese true for my sprinkler? I increase from 3/4" to 1"...why doesn't pressure go down?
Take a look at the attached graph in PDF format, I hope this helps, you are never increasing pressure anywhere, your only reducing flow to keep the pressure from dropping further. The three lines on the graph represent a standard 50 foot length of straight pipe, in 3 different sizes, 1/2", 3/4" and 1". When you go larger in size, your able to flow MORE water with a less pressure drop. When you try to squeeze more water through a smaller pipe, your pressure drops off like a cliff like you see on the 1/2" graph line.
Attached Files
 WaterGraph.pdf (61.3 KB, 177 views)

07-01-2010, 10:48 PM   #21
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Quote:
 Originally Posted by The Engineer Yes, it doesn't matter if he puts in a 1" pipe or a 12" pipe, the pressure will be the same 80 psi. Pressure loss is a function of flow rates through specific pipe diameters and distances, so he might actually gain a fraction of a pound under residual flow because the friction loss through a 1" pipe is less than a 3/4" pipe under the same flow rate. His old choke point or bottleneck was where the pipe changes from 3/4" to 1/2", now that he's putting in a 1" pipe after the meter, his new choke point will be the 3/4" service line from the street when the sprinklers are on. Going larger pipe size increases residual pressure, but since his length of 1" pipe is short, the increase is minimal. For example: Using 80 psi static pressure as a starting point 10 gpm through a 50 foot 1/2" pipe will loose 44 psi, the pressure at the end of that run will be 36 psi. 10 gpm through a 50 foot 3/4" pipe will loose 6 psi, the pressure at the end of that run will be 74 psi. 10 gpm through a 50 foot 1" pipe will loose 1.5 psi, the pressure at the end of that run will be 78.5 psi. That why you sometimes see larger pipe diameters inside the homes with street pressures in 40-50 psi range, they need to keep friction loss down to maintain 30 psi minimum at the fixtures. He has 80 psi static pressure, so thats why they put a 1/2" line to feed his entire house and he's not having problems with pressures when multiple fixtures are running, he has almost 50 psi of pressure available for friction loss.
That all makes sense I think as long as i'm not misreading you, but what i'm saying is that you're feeding a 1" line AND a 1/2" line with a 3/4" line. Seems to me that when the sprinkler system is operating depending on how the sprinkler system was sized, he's going to have a pressure drop, and it'll be more noticeable in the house.

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 07-02-2010, 12:20 AM #22 Just call me Andrew   Join Date: Mar 2009 Location: Albany, NY Posts: 2,265 Rewards Points: 1,020 Well due to the town requiring watering at 1:00-4:00 AM, even if there is a pressure drop, i'm not worried about it. Based on the above posts...since I measured 80 PSI at the hose bib outside, which is fed with about 30 feet of 1/2" pipe. Since 1/2" pipe gives a huge pressure loss...if i feed right off the meter with 1", I should have tons of pressure, right? Maybe even requiring a regulator? Ideally, I want about 70-80 PSI on the 1" pipe to feed the system. I am understanding a little better, still have a way to go though. __________________ Andrew
07-02-2010, 12:44 AM   #23
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Quote:
 Originally Posted by secutanudu Since 1/2" pipe gives a huge pressure loss...if i feed right off the meter with 1", I should have tons of pressure, right? Maybe even requiring a regulator?
No, the pressure loss is during use.
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 07-02-2010, 07:35 AM #24 Just call me Andrew   Join Date: Mar 2009 Location: Albany, NY Posts: 2,265 Rewards Points: 1,020 I meant pressure for the sprinkles...not the rest of the house. __________________ Andrew
 07-02-2010, 09:45 AM #25 Member   Join Date: May 2010 Location: Massachusetts Posts: 133 Rewards Points: 75 How many sprinkler heads do you plan on putting outside? You need to determine what the demand for the sprinkler system will be and how many and how far apart you place the heads. Each head could be between 1-5 gpm and if you have say 4 heads, your demand could be anywhere between 5-20 gpm depending on the type and size of sprinkler you are using. Sprinklers only require between 30-40 psi so your system will be able to handle a decent sized sprinkler system. Once you know the GPM load, we are better able to pinpoint what pressure you'll see at the sprinklers. This link might help you along http://www.lawnbeltusa.com/design.htm
07-02-2010, 09:47 AM   #26
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Quote:
 Originally Posted by Alan That all makes sense I think as long as i'm not misreading you, but what i'm saying is that you're feeding a 1" line AND a 1/2" line with a 3/4" line. Seems to me that when the sprinkler system is operating depending on how the sprinkler system was sized, he's going to have a pressure drop, and it'll be more noticeable in the house.
I agree, he will see some pressure drop in the 3/4 service pipe from the street, but the 1" will keep the pressure drop from dropping further under higher flow rates.

 07-02-2010, 10:06 AM #27 Just call me Andrew   Join Date: Mar 2009 Location: Albany, NY Posts: 2,265 Rewards Points: 1,020 I haven't started to design my system yet. I planned on using guides from Hunter to figure it out. My front yard is only about 40x40, so probably 4-6 rotary heads (probably just one per corner). I can't imagine needing more than 4-5 heads active at any one time. In total, front and back, I'll probably have 2-3 zones of rotors (3-5 per zone), and 1-2 zones of spray heads for small areas and shrubs/flowers. I have read a bunch of those design guides, and the thing that bugs me is they always tell you to measure your gallons per minute at your spigot...when it won't be at all accurate...unless i plan to feed my sprinklers with 1/2". I think my plan is to plumb in the 1" feed, install both boiler drains (inside and out), then cap it and test for pressure and GPM on the outside drain. That'll give me my starting point. Then i'll design the sprinkler system (how many heads per zone and where to put them), since i'll know how much volume I have to work with. Does that make sense? I will leave room for a pressure regulator upstream of the backflow preventor...just in case. __________________ Andrew Last edited by secutanudu; 07-02-2010 at 10:16 AM.
 07-02-2010, 11:54 AM #28 Just call me Andrew   Join Date: Mar 2009 Location: Albany, NY Posts: 2,265 Rewards Points: 1,020 Is there an advantage to using a brass tee over a cheaper copper tee? I actually found a 1"x3/4"x1/2" brass threaded tee - which is perfect for my setup right after the meter, but it's pricey (\$20). I assume this is better than, say, getting a 1x1x1/2 tee and reducing one of the 1" sides to 3/4" with a bushing? Or am I better off just using a copper tee that is all solder, no threads? __________________ Andrew
 07-10-2010, 11:41 PM #29 Just call me Andrew   Join Date: Mar 2009 Location: Albany, NY Posts: 2,265 Rewards Points: 1,020 So I have started my piping. I cut the tee in after the meter and ran a few feet of 1" copper to the valve. I can now close the valve on the sprinkler branch and work on the sprinkler system with the rest of the house water still on. What's the best way to clamp the pipe to the wall? There is concrete block directly behind the paneling, and the pipe is 1-2" from the wall. For now, I have a piece of wood under the pipes so there isn't a ton of weight on the soldered joints. Thanks Attached Thumbnails   __________________ Andrew
07-11-2010, 09:01 AM   #30

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You can't design anything until you know the GPM flow rate at the point of delivery. PSI tells you nothing. You can have a whole lot of pressure and next to no volume. sprinklers are pretty high volume fixtures.

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