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Re: [Electronics_101] pressure/vacuum switches

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  • Roy J. Tellason
    ... No, I m thinking it s inches of mercury. But let me grab the gauge, which I happened to notice up here rather than out in the car. Yep, says INCH Hg
    Message 1 of 13 , Apr 1, 2006
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      On Saturday 01 April 2006 03:01 pm, Stefan Trethan wrote:
      > On Sat, 01 Apr 2006 21:32:04 +0200, Roy J. Tellason
      >
      > <rtellason@...> wrote:
      > > Typically specified in "inches" for me (I can get my vacuum gauge at some
      > > point and see what else it's marked perhaps), a value of 16-18 inches
      > > with a steady reading is considered normal for the stuff I work with.
      >
      > that would be about half a meter, if this is "inches of water" and not
      > "inches of mercury" (that's kinda important, inches alone is not really a
      > useful measurment) it would be about 0.05 athmospheres, far too sensitive
      > for my needs.

      No, I'm thinking it's inches of mercury. But let me grab the gauge, which I
      happened to notice up here rather than out in the car. Yep, says "INCH Hg"
      and also "-kPa" on the inner scale, which strikes me as being one of those
      metric-type measurements. <g> I was a bit off on "normal", too, the range
      there is 18-22 or 60-70, roughly.

      Hope this helps some.

      --
      Member of the toughest, meanest, deadliest, most unrelenting -- and
      ablest -- form of life in this section of space, a critter that can
      be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters"
      -
      Information is more dangerous than cannon to a society ruled by lies. --James
      M Dakin
    • Stefan Trethan
      On Sat, 01 Apr 2006 23:20:53 +0200, Roy J. Tellason ... 60-70kPa would be about right, 100kPa is 1bar or about one athmosphere. thanks ST
      Message 2 of 13 , Apr 1, 2006
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        On Sat, 01 Apr 2006 23:20:53 +0200, Roy J. Tellason
        <rtellason@...> wrote:

        > No, I'm thinking it's inches of mercury. But let me grab the gauge,
        > which I
        >
        > happened to notice up here rather than out in the car. Yep, says "INCH
        > Hg"
        >
        > and also "-kPa" on the inner scale, which strikes me as being one of
        > those
        >
        > metric-type measurements. <g> I was a bit off on "normal", too, the
        > range
        >
        > there is 18-22 or 60-70, roughly.
        >
        >
        > Hope this helps some.


        60-70kPa would be about right, 100kPa is 1bar or about one athmosphere.

        thanks

        ST
      • Dave Mucha
        ... lower ... and run ... washing ... If you have anything of a regular gauge, it is most likely a Borudon Tube type with an internal bent tube connected to a
        Message 3 of 13 , Apr 1, 2006
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          --- In Electronics_101@yahoogroups.com, "Stefan Trethan"
          <stefan_trethan@...> wrote:
          >
          >
          > Hi,
          >
          > i would need a switch to activate a pump if the pressure is under a
          > certain level of vaccum (say 1/3rd athmosphere or thereabouts).
          >
          > Like the switches you get for compressors, only for vaccum and for a
          lower
          > range (or i would simply put the compressor switch in a sealed tin
          and run
          > it reversed).
          >
          > I was thinking of pressure switches like used in dishwashers and
          washing
          > machines, like
          >

          If you have anything of a regular gauge, it is most likely a Borudon
          Tube type with an internal bent tube connected to a small rack and a
          gear on the needle.

          these are calibrated for their purpose, but I am pretty sure you can
          use them and pull a vacume and have it run in reverse.

          Here is what I would do.

          open the gauge and look at the gear and mechanism. then bend either
          the tube or gear so it would have the needle start at the top of the
          meter and then move in reverse with a vacume.

          Calibration is not that hard. just take a tube in a bucket of water
          with a measuring tape. use a vacum cleaner and see how far up the
          water moves and how much the meter moves. A residential vaccuum
          cleaner pulls about 8 inches. ( Wish I could remember if that was
          inches or water or inche of mercury)

          Anyway, put glue a disk on, over the needle and put on your
          opto-switch on that disk. clear is one state and black would be the
          other.

          El-cheapo. but very workable.


          I forgot to mention that you need to start with a meter that is about
          15 PSI to show a full vacuum, a 30 PSI gauge would not have as much
          movement.

          But, you didn't mention what level of vacuum you wanted to pull. that
          would indicate what alternatives might work.

          Here is a link on the inside of a pressure gauge.
          http://www.answers.com/topic/pressure-gauge
          About half way done the page.

          #5 is the sensitivity adjustment. The relationship is how far that is
          between the two point on it.

          And, as I recall, use of such a gauge in this manner will be VERY
          non-linear, and also only have a short distance.

          Dave
        • Stefan Trethan
          This is exactly what i did to make the positive pressure switch. But even with the sensitivity full up the gauge i tried didn t move enough for that half
          Message 4 of 13 , Apr 1, 2006
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            This is exactly what i did to make the positive pressure switch.
            But even with the sensitivity full up the gauge i tried didn't move enough
            for that half athmosphere or so for vacuum. Would probably just work with
            a light barrier sensor but surely not for two (for hysteresis) like i
            arranged it for the positive pressure. Well, maybe if i put one on the
            other end of the pointer...

            Calibraition is not an issue, i have a vacuum gauge (for the panel,
            hacking it up is a no-no), also the goal is only to shut the motor off
            when "almost all" it can pull is reached, to prevent it running all the
            time with no work done, no calibration needed.

            ST



            On Sun, 02 Apr 2006 01:33:44 +0200, Dave Mucha <dave_mucha@...>
            wrote:

            >
            >
            > If you have anything of a regular gauge, it is most likely a Borudon
            >
            > Tube type with an internal bent tube connected to a small rack and a
            >
            > gear on the needle.
            >
            >
            > these are calibrated for their purpose, but I am pretty sure you can
            >
            > use them and pull a vacume and have it run in reverse.
            >
            >
            > Here is what I would do.
            >
            >
            > open the gauge and look at the gear and mechanism. then bend either
            >
            > the tube or gear so it would have the needle start at the top of the
            >
            > meter and then move in reverse with a vacume.
            >
            >
            > Calibration is not that hard. just take a tube in a bucket of water
            >
            > with a measuring tape. use a vacum cleaner and see how far up the
            >
            > water moves and how much the meter moves. A residential vaccuum
            >
            > cleaner pulls about 8 inches. ( Wish I could remember if that was
            >
            > inches or water or inche of mercury)
            >
            >
            > Anyway, put glue a disk on, over the needle and put on your
            >
            > opto-switch on that disk. clear is one state and black would be the
            >
            > other.
            >
            >
            > El-cheapo. but very workable.
            >
            >
            >
            > I forgot to mention that you need to start with a meter that is about
            >
            > 15 PSI to show a full vacuum, a 30 PSI gauge would not have as much
            >
            > movement.
            >
            >
            > But, you didn't mention what level of vacuum you wanted to pull. that
            >
            > would indicate what alternatives might work.
            >
            >
            > Here is a link on the inside of a pressure gauge.
            >
            > http://www.answers.com/topic/pressure-gauge
            >
            > About half way done the page.
            >
            >
            > #5 is the sensitivity adjustment. The relationship is how far that is
            >
            > between the two point on it.
            >
            >
            > And, as I recall, use of such a gauge in this manner will be VERY
            >
            > non-linear, and also only have a short distance.
            >
            >
            > Dave
            >
          • Stefan Trethan
            problem solved - i hope. i put a spring inside the water level sensor, well, it will now act as a vacuum switch but the pressure is way too low, one would need
            Message 5 of 13 , Apr 3, 2006
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              problem solved - i hope.

              i put a spring inside the water level sensor, well, it will now act as a
              vacuum switch but the pressure is way too low, one would need a very, very
              strong spring (maybe 20kg / 200N force). This doesn't work.

              So the membrane is too large.

              Then i thought of the solution: a thermostat.
              A thermostat like in a fridge or freezer or heater of some sort is only a
              metal bellow and a tube in which a gas is expanding due to heat. So i took
              a old one and opened the tube end, and found it will react to 1 to 2
              positive athmospheres of pressure depending where the control knob is set.
              I'm positive this is fairly easy to modify it slightly so it will react at
              a slightly lower pressure, and i will put it in some kind of container and
              seal the wiring so it works with vacuum instead of pressure.


              Seems like i found a $0 solution after all - tried for the analog pressure
              sensors at ebay but they ended up too expensive.

              ST
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