3/4" copper vs 1/2" copper

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by MeanRoc, May 23, 2011.

  1. MeanRoc

    MeanRoc New Member

    Messages:
    2
    Location:
    Saskatchewan
    I was just wondering what would result from me replacing my half inch copper pipe with three quarter inch, will I have less pressure but more volume, more pressure more volume, will my lawn sprinkler spray farther or will I just be able to run more at the same time?? This may sound like a stupid question, but if you have the time I would really like to know. Thanks.

    Last edited by a moderator: May 26, 2011
  2. countrylife

    countrylife New Member

    Messages:
    3
    Location:
    Texas
    The correct answer is "sort of", "none of the above", and "all of the above". I don't really mean to be a smart a$$, but the answer depends on the source of the water, the flow rate, and the length of pipe. First the source, you will never get more pressure or volume than what it is capable of. This is normally a pressure/GPM curve so you would not expect to get the same volume at 10 psi that you would at 60 psi. Second the flow rate and the length of pipe. There is friction between the pipe and water as the water flows thru the pipe. The smaller the pipe the more friction than a larger pipe (for the same GPM flow rate). Also, the friction accumulates per foot of pipe, so each foot of pipe causes more friction. The friction results in a pressure drop at the end of a pipe. A larger pipe will reduce the pressure loss. However, if you are using this for potable water, you can go to far in increasing the pipe size and end up with stagnant water in the pipes because not enough of the volume is being used. I don't know were this starts becoming a concern but I've heard something on the order of 1.5" to 2" main supply for a house should be the largest used.

    Note: There is no friction when the water is not moving so you will get the same pressure at the end of a long run until you turn on the water. - Have you ever turned on a faucet and got a lot of water which gradually slowed down? That is the effect of a pressure loss due to friction.

    Bottom line: I didn't answer your question directly. In general if you're just replacing it with no other change, you'd see an increase in pressure. But, the improvement may not be worth the cost of the pipe.
  3. SacCity

    SacCity In the Trades

    Messages:
    189
    Location:
    Sacramento, CA
    How much pipe are you changing?
    Your pressure will remain constant, when measured statically ie no flow.
    Volume of water flow will increase for the same pressure, volume of 3/4" pipe is about twice that of 1/2" pipe.
    Michael
  4. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    3,967
    Location:
    NW Ontario, Canada
    It would depend how long the run is and how much water you are trying to use. You would not lose any pressure. There could be more volume and if there is a pressure drop now due to reduced volume, more pressure too.
  5. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Flow in a pipe is restricted by the size of the pipe, and the friction pressure loss is function of length.

    A given main supply will have a capacity to deliver x gallons per minute at minimum pressure drop. If you use too-small and/or too long pipe, you will possibly have less than desired pressure or gallons per minute at the end. Once you get up to "normal" pipe size for the length and flow, there is little advantage to going bigger. You can't make it any better...you can only make it worse.

    Sprinkler system design involves dividing the area into zones so that no zone requires more gallons per minute than your supply can deliver. Then you also have to make the pipes large enough that they do not rob your pressure.
  6. MeanRoc

    MeanRoc New Member

    Messages:
    2
    Location:
    Saskatchewan
    Thanks for all the advice guys, it gives me some new things to consider. I was mainly thinking I would run 3/4" up to and through my water softner and hot water tank, then straight out the house with two outside taps, one hot one cold. I was hoping by doing this I would improve my outside water situation. It just seems like by the time I hook up 50' of garden hose I lose so much pressure that I can hardly water my garden.
  7. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,347
    Location:
    Yakima WA
    Actually, you are not losing pressure, you are losing flow. What size hose are you using? If you went for the cheap stuff, you might have 1/2" hose which over 50 feet would lose a great deal of flow due to friction. 3/4" hose is far better for maintaining flow over distance. Use your math to figure the area of a circle and compare the different hose sizes. The greater the area, the less friction loss.
  8. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
  9. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,107
    Location:
    Houston, TX
    Not sure about this statement "Actually, you are not losing pressure, you are losing flow" ???

    Actually you do lose Volume and Pressure, because pressure is all you have to overcome the hoses resistance/friction.

    I do believe... The Bigger the hose the better.


    P.S. OR You can run underground .75 or 1 inch PVC to the garden and use a shorter hose.


    DonL
    Last edited: May 25, 2011
  10. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,607
    Location:
    Cave Creek, Arizona
    quote; I was just wondering what would result from me replacing my half inch copper pipe with three quarter inch, will I have less pressure but more volume, more pressure more volume, will my lawn sprinkler spray farther or will I just be able to run more at the same time??

    THere is absolutely no "postive" answer we can give. IF the existing line is inadequate for the demand on it, then a larger pipe will give more volume, assuming the supply line TO it is also adequate. IF the length is excessive, then a larger line will have less friction loss and the volume will also increase. Pressure at the head is a function of many different items, including the head itself, so it is impossible to tell you empirically whether it will go up, down, or remain the same.
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