DIY - Drip system

Discussion in 'Irrigation / Sprinkler Forum' started by Oleg30, Mar 17, 2011.

  1. Oleg30

    Oleg30 New Member

    Alberta, Canada
    Hi All,

    I'm looking for you plumbing experience advice on the task i'm trying to accomplish.
    Apologies for posting this question in the general thread since did not find a better place to post.

    I'm trying to build a drip system that would be connected to both cold and hot water (tank) supply and would drip on the end. The system should:

    1. allow controlling precisely (at least in steps of 1 gph) the flow rate down to full stop.
    2. provide steady controllable water temperature (70F and up) at the outcome at the low flow rate (0.01 gpm)
    3. be fault tolerant, meaning if the cold water supply stops the flow should stop, if hot water supply stops it should continue on the cold water.
    4. long lifetime
    5. use 1/2 inch pex for connectivity

    I've done a bit of research and my thoughts are:

    1. irrigation emitters can be used to precisely control the flow rate
    2. low temperature T/P mixing valve can be used, but most manufacturers claim a steady operation with a flow over 0.5 gpm, which is much higher than 0.01 gpm. May be instead use pressure balanced mixing valve with the sort of temperature controller?
    3. add additional "T" section to manually override the mixing valve?
    4. ?
    5. should not be hard to find various connectors.

    thank you!
  2. hj

    hj Moderator & Master Plumber Staff Member

    Cave Creek, Arizona
    #2 may be impossible to control, since at that flow rate the water would NOT maintain its temperature to the end of the run. Pressure balanced valves are NOT smart enough to do what you desire in #3. They will NOT continue flow regardless of whether it is the hot OR cold water which fails.
  3. jimbo

    jimbo Plumber

    San Diego
    Just what is your project?? Irrigation of gardens does not require the precision and small numbers you mention. What you are trying to do would require precision industrial controllers. What/s with the hot water?
  4. dejswa

    dejswa New Member

    dallas, TX
    I have done lots of drip systems.

    Yes, I have the same question. What is your application? Why is temperature important? Precise delivery of water at the exact temperatures will likely be impossible without complex delivery apparatus. For example, here is an evaluation of equipment available to medical personnel for accurate delivery of warm IV fluid to a patient. The systems cost around $700 and only deliver at one temperature. You have to have a heat exchanger all the way out to your delivery point if you want to deliver warmed fluid at a very low flow rate else the fluid just cools down to the ambient temperature.
  5. Oleg30

    Oleg30 New Member

    Alberta, Canada
    Thank you for the replies!

    The application for this drip system is not for planting but for the tropical fish tanks.
    the most important part is to get the steady temperature on the outlet's not a big deal if it fluctuates 2 F (plus/minus).....under the low flow rate. But both the flow rate and temperature needs to be adjustable. It's not the must to have a cold water continue to run in case if hot water supply stops, since possible to add an "override" on the cold pipe...and switch manually when needed.

  6. Oleg30

    Oleg30 New Member

    Alberta, Canada
    Why at the low flow rate the water would not maintain its temperature? Mixing valves typically employ a wax thermostat to control water temperature. The thermostat is located in the mixing chamber of the valve. The thermostat wax expands when heated. This expansion activates a rod, which in turn operates the valve. The specific composition of the wax determines at what temperature it will expand. Do you know how flow affects the mechanism?
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