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Pressure in a 2" pipe branching into four 1" pipes

  1. Oct 8, 2018 #1
    Hello all,
    I am an Electronics Engineer, working in an R&D Organisation specializing in Electronics and Advanced Computing. My area of work is Control & Instrumentation related to Industrial Automation.

    I am trying to identify the a solenoid valve to be used on a 2" pipe. For this I need to know the pressure in the pipe.
    Water flowing in a pipe of 2" diameter is branching into 4 pipes having 1" diameter. At the output of the 4 pipes there is a sprinkler, which works at a pressure of 120 psi. The main pipe is connected to a pump having 10 HP motor. i.e. Water pumped from a 10 HP Pump flows through a 2" diameter pipe and branches into 4 pipes of 1" diameter before flowing out through sprinklers.

    I would like to know the pressure in the 2" Main Pipe.

    Thanks in advance.
    Senju Panicker
  2. jcsd
  3. Oct 8, 2018 #2


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    Science Advisor
    Homework Helper

    Hello Senju, :welcome:

    Here at PF we always encourage some poster initiative. Did you google a few things ? If so, what popped up ?

    Your question doesn't constitute a complete problem statement: pipe lengths, flow rates, geometry ?
  4. Oct 8, 2018 #3
    And pump characteristics (flow vs head), sprinkler characteristics (orifice size, dP vs flow), probably more info once an analysis begins.
  5. Oct 8, 2018 #4


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    Staff: Mentor

    If this is a real sprinkler system and 120psi is the in operation pressure (that would be a lot - is it static?), the piping loss is unlikely to add significantly to that.

    ...however if this is more than an academic exercise, you're likely required to do a full fledged hydraulic calc and get it stamped by a professional engineer.
  6. Oct 11, 2018 #5
    If you are looking for a proper calculation you will have to make a drawing/sketch with exact lengths of each pipe. The height at the beginning and end of each pipe should be indicated
    Any bends, valves etc will have to be indicated.
    If you can supply the pump curve that would be very useful. Alternately you can supply the pump type or model number and somebody might have it(unlikely).
    What you have described can be anything from a irrigation system for small farm or greenhouse to a fire reticulation system for a small hotel. It's difficult to give you proper advice.

    If you want to know the pressure at an exact point the best thing to do is to install a pressure gauge. Calculations are estimates. A pressure gauge is an actual measurement. It's good practise to have a pressure gauge at the outlet of a pump anyway so I think this is the best route.
    Last edited: Oct 11, 2018
  7. Oct 11, 2018 #6


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    @Senju Panicker was last seen monday 11:20, so he/she hasn't even see the first response....
  8. Oct 11, 2018 #7
    Yeah well. It's obviously not that urgent. He'll show up sooner or later though.It's all chill...
  9. Oct 25, 2018 #8
    Hi everyone,

    Thank you for the replies. Sorry for being late. I was expecting a notification in my email, since I was getting other notifications from this site. I should have checked here. And I was really busy with other work related to the problem I had posted. Sorry.

    I have googled a little. But couldn't understand most of things. So thought of posting it here.

    This is is a sprinkler system. I don't have any info of the pump. The system is at a remote place and I still haven't been able to get the details of the pump or the sprinkler. All I have is few photographs and some minimal info. As of now, I am forced to start with some assumptions.

    The problem statement is
    A 2" Main pipe is branching into four 1" pipes. The 2" pipe coming from the pump is horizontal and is on the ground. The 4 branches are vertical with a height of around 2.5 m. There are four sprinklers at the end of the four 1" pipes. I need to connect a Solenoid Valve in the main pipe.
    Don't have any idea regarding the pump (except that it works from a 10 HP motor). Don't have much idea regarding the sprinkler as well. I am guessing a pressure of about 6 to 8 bar is required for the sprinkler to work. The sprinkling distance is 20 m.
    Trying to figure out what is the pressure to consider while looking for solenoid valves.

    Looking forward to helpful suggestions. Will check frequently this time around.

    Thanks in advance.
  10. Oct 25, 2018 #9
    Are you trying to specify design pressure for the valve?

    When the solenoid valve is closed, the upstream side of the valve will see the pump shutoff head. Assuming it is a centrifugal pump. If it is some kind of positive displacement pump it should have an integral safety/relief valve. In that case the valve will see the same pressure as the relief setting.
  11. Oct 26, 2018 #10
    A total of 10 solenoid valves are planned to be connected along the main pipe coming from the Pump. Each solenoid valve will activate 4 sprinklers each.

    Usually, when the pump is operated one solenoid valve is opened, while the rest 9 nos will remain closed. But accidentally, the pump might be operated even when all solenoid valves are closed. (Note: The fully automatic system being designed has a manual option as well)

    As mentioned in the previous post, if a pressure of 8 bar is needed for the sprinkler to operate, what should be the pressure rating of the solenoid valve. Will it be same as 8 bar or will it be 4 times (32 bar)?

    I had referred to this previous post in Physics Forum when i googled for help. That's how I came to this forum.

    I got confused on reading it. Sorry. Not so very good at fluid dynamics.

    Kindly help me out.
  12. Oct 26, 2018 #11


    Staff: Mentor

    To be safe, the system should not be damaged if the pump starts when all the valves are closed. That means following this answer from an earlier post.

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