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bkloos

Tapping the main water line

bkloos
13 years ago

Hello All,

I am designing my irrigation system for the front and side lawns. I used the help of rainbirds design system and have a rough sketch that I will tweak.

My question is how to tap the main water line...

I have a 1 1/4" galvanized??? water line coming into the basement from the service. It then reduces to a 5/8" copper line which passes through the meter and then reduces to a 1/2" copper line that feeds the house.

My thoughts were to cut into the 5/8" post meter, add a T fitting and then increase up to 1 1/4" pvc for my run to the manifold out front? While I have restriction, there is only about 1' of 5/8" including the meter so I was hoping that this short distance wouldn't cause too much restriction.

Is running 1 1/4" to the manifold overkill?

I was testing 8-9gpm at an outside faucet running through the 1/2" line, so my goal here is to increase total gmp to the manifold.

Thoughts?

Thanks,

Bryan

Comments (7)

  • lehua49
    13 years ago

    bk,

    What pressure is coming out of the faucet? Do you have a pressure regulator in your system before the line continues into the house? The max flow for a 5/8" diameter Cu line is around 9 gpm, the max flow for 1/2" line is 7 gpm. You will have to tap after the meter, but if the run of 5/8" is less than 5 feet, you will have the max available flow of the 1 1/4" line which would be 23 gpm. The velocity through the meter and 5/8" line will be very high, probably noisy and shorten the life of the meter( and increase your bill). Your water company may not allow it. If the 5/8" is longer than 5 feet, it will restrict the flow to around 8 gpm. Any one disagree with this analysis. I am not quite sure that I have the theory correct. The component relationships are Flow(gpm) equals Velocity times pipe cross section area. There is a maximum flow for certain size pipes and certain pipe materials(interior roughness) To realize 8-9 gpm from 1/2" pipe means you have very good pressure. JMHO Aloha

  • homr
    13 years ago

    Use caution when designing a sprinkler system off of a house that has a galvanized pipe water supply. Galvanized pipe generally means your house is old and was plumbed that way prior to copper being used. As galvanized pipe ages, it corrodes from within. That means that the interior opening size of the pipe is somewhat smaller than what it was when it was installed years ago.You may , now have only the capacity of a comparable 1" or even 3/4" pipe. How did you determine that the pipe is 1 1/4"? . A small restriction, such as you have is still a factor you have to consider. You can not push 15 -20 gpm through a small hole and not expect it to have some impact. Also consider the size of your water meter. Static water pressure and length of the galvanized pipe are also factors. If you are not willing to replumb the piping just before and just after the meter with larger pipe then I would say just be conservative in how much water you want to flow. Either way, I would say that a 1 1/4" pvc main is not needed and a 1" pipe would be sufficient. You can safely run around 14 gpm and be within the 5 ft./sec velocity limit.

  • bkloos
    Original Author
    13 years ago

    Hey Guys,

    Thanks for the replies.

    I was guessing about the main line being galv, as it is old. The house was build in the late 40's, and the main line enters directly into the house from a run starting at the street.

    As the pipe enters the house, ot passes throught a large ball valve (main line cut-off), the a 90 deg elbow, then reduces to 5/8 throught the meter and then reduces again to 1/2. The total length of pipe including meter ane cut-off valve is about 2-3 feet before the final reduction to 1/2 copper.

    My pressure at the nearest outdoor faucet which is the nearest outlet from the meter is ~65psi.

    The meter is brand new, just replaced a few weeks ago by the water company.

    I cant replumb before the meter for obvious reasons, so I am limited to a T off the post meter line.

    So you think I should run 1" PVC up and out of the house?

    Another option would be to install the T and then test the new unrestricted flow directly in the basement and determine accurately the flow?

    THat siad, if 1" line will get me enough water to the manifold, I would be content with that!

    Thoughts?

    Bryan

  • homr
    13 years ago

    In my area of the world, I do not see 5/8'copper for water service. 3/4" is the smallest we see here. You might want to double check that size, although every area has its own standards. Good idea to check your flow at the point of connection. What size meter did the water co. put in? You really should verify the type of pipe coming in. 1 1/4" copper would not have the possible corrosion problems as I mentioned earlier with galvanized. 1" sch. 40 pvc should be sufficient if your going to run 14-16 gpm.

  • lehua49
    13 years ago

    bk,

    homr is right on. I am used to seeing 5/8" meters on smaller lot houses in higher density areas. The calcium build up over time can reduce the rougher interior diameter of a galv. pipe quite substantially. If you can hear the water flow loudly in the galv. pipe, the I.D. has been reduced. The meter size should be somewhere on the meter body. 1" pipe would be adequate although for long runs a 1 1/4" pipe reduces the velocity and thus the noise inside the pipe if you don't mind spending the extra money. 65 psi is very good pressure for an irrigation system and slightly high for a house. I like the idea of hooking in the tee and seeing what you get. Watch out for the irrigation system pulling the water out of your lines in the house and when not running getting shove back in. Maybe a backflow preventer on the house line side. JMHO Aloha

  • bkloos
    Original Author
    13 years ago

    Hey guys,

    I went back to the source and took a better look.
    I'm not really sure now the size of the main. I know it is at least 1", and possibly more. The problem is that there are a bunch of couplings and sleves on the pipe as it enters the house. The main shut-off is at least a 1" ball valve, which then feeds to a reducing elbow to 5/8, through the meter (5/8 in and out) and then the final 1/2 reducer.

    I'll poke around the plumbing supply this weekend and see if I can find the parts to install the T and a valve. From there I will measure the flow and pressure and report back. We can better decide on the plumbing at that point.

    I am planning on a RP backflow preventer in the basement. My only concern is where/how to handle the purge. I dont have a drain in the near vacinity.....

  • Michael
    13 years ago

    Bryan: I have a reference book that I use to, amongst other things, look up pipe sizes of many types and sizes. the measurements given are for outside circumference which is what matters most when trying to size pipe and fittings. One of my suppliers also was kind enough to give me a thin, flat tape measure graduated down to 10 ths of an inch which is what the table gives the sizes in. If I remember, I'll look up the sizes you are referring to and post them.

    We use 2 different meter sizes here, 1/2" and 5/8" x 3/4". A 5/8 x 3/4 meter is necked down by one nominal trade size within the meter body to increase the flow velocity through meter thereby giving a more accurate measurement of the actual flow. It is definitely possible to plumb past the meter with 5/8 or 3/4" pipe, our town uses 3/4" routinely except when we run into an installation where some ding dong penny pincher used 1/2" many years ago.

    FWIW - with copper pipe used in plumbing:

    "Nominal" = the inside diameter of the pipe which varies by thickness of the pipe.
    O.D. = outside diameter and is a constant size, it is always 1/8" larger than the nominal size. I.E. 1/2" nominal is always 5/8" O.D.