Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How does this work? Fluid Mechanics question (?) regarding garden hose attachment

  1. Aug 16, 2011 #1
    Okay, I should just go buy one and look at it, but just wanted to do some background research on it. I want to use it to dose dechlorinator into an aquarium and wanted to think if this will work. Yes, they sell VERY expensive ones for this purpose, but why spend more when you don't have to?


    Anyway, is this like a venturi pump? I'm guessing the pressure from the flowing water creates a suction?

    I'm an electrical engineer, so I have basic physics background (for the purposes of knowing how much to dumb it down for me :P )

    Thanks in advance!
    Last edited by a moderator: Apr 26, 2017
  2. jcsd
  3. Aug 16, 2011 #2


    User Avatar
    Homework Helper

    Re: How does this work? Fluid Mechanics question (?) regarding garden hose attachmen

    Open one up and take a look at it. Part of the water flow is directed into the chamber, then exits and recombines with the main water flow out the spray nozzle. The ideal is to only release a small amount of the fertilizer per unit time.

    There are venturi based devices that you hook up to a tap that generate enough low pressure to drain water from an aquarium or basement. Example of an aquarium version:

  4. Aug 16, 2011 #3
    Re: How does this work? Fluid Mechanics question (?) regarding garden hose attachmen

    Do you know what this technique or system is called? I can't seem to find anything on the internet, but I'm probably looking for the wrong search terms. For instance, it took me a while to figure out the draining system was actually using a venturi pump. At which time, I found a ton of online and textbook references to it. I have no problems going to a library.

    I know about the aquarium and water bed units, but that's not quite what I'm looking for. I use active pumps to drain because venturi is to wasteful and besides, I can can keep a passive siphon going for draining with just plain old gravity.

    I kind of want a system to dose a chemical (similar to what the fertilizing attachment is doing). I actually do WANT a slow mix (i.e. high concentration of dechlorinator solution exchanging with a large volume of water). I can dilute or increase the concentration of the dechlor as required for the volume passing the unit per whatever unit time.

    So water enters the garden hose attachment, mixes, and then sprays out is my intention, so slow mix is perfect.

    The other reason I want to do this is because I like to do DIY stuff to learn, so I wanted to see if I can build it myself. Yes, I know it's pretty cheap, but it's about learning here :)

    So my goal is, figure out a way to build it if possible. If not, figure out how to adapt an existing system and repurpose it for my use.

    The other advantage of building it myself is that it may be possible to build it to my specifications (i.e. thread type, pipe diameter, reservoir size, and dose rate).

    I guess I'll just go and buy it, it's pretty cheap.

    Thanks :)
  5. Aug 18, 2011 #4
    Re: How does this work? Fluid Mechanics question (?) regarding garden hose attachmen

    Well, just in case some curious individual in the future comes upon this thread looking for the same thing, I'll go ahead and briefly list what I found...

    Some of the units for irrigation using all sorts of methods to dose chemicals. Passive ones like those found at the hardware store use venturi methods. Some other ones, often used in labs and for aquariums use peristaltic pumps. Of course, that's just what I've gleaned out of in the last couple days. Seeing as I have a real job and grad school, I haven't had time to dig more deeply in that.

    After that, the world opens up and there's plenty of information when you look up peristaltic pumps and venturi pumps.
  6. Aug 18, 2011 #5


    User Avatar
    Homework Helper

    Re: How does this work? Fluid Mechanics question (?) regarding garden hose attachmen

    The internals of the aquarium unit look like this (link to image, I attached it in another thread and not allowed to attach it again). Figure 4 shows it in drain mode, Figure 5 has the end cap closed for fill mode:


    Some of the non pre-mix hose end sprayers (these look like the Gilmour 405 or 499 or Ace 405AC) don't use a syphon tube. Instead some of the water flow is simply directed into the cannister, churning in the cannister to mix with the fertilizer and the mixture flows back up into the main flow (I don't remember if these input and output openings were just holes or small nozzles). Others that look like the Gilmour 385 or 390 do use a venturi tube with a bottom hose to draw a pre-mix solution from the bottom of the cannister. I'm not sure how ones with a brass mixing head like the Gilmore 362 work.
    Last edited: Aug 18, 2011
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook