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Re: [Electronics_101] pressure/vacuum switches

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  • Roy J. Tellason
    ... 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
    Message 1 of 13 , Apr 1, 2006
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      On Saturday 01 April 2006 02:19 pm, Stefan Trethan wrote:
      > Yes, those might be the switches that look like tiny flying saucers.
      >
      > Maybe someone has an idea what vacuum range a motor will have?

      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.

      > Where it this vacuum present? at the intake to the cylinder?

      There are two kinds, on the stuff I have. "Ported" vacuum is going to be
      somewhere above the throttle plate on the carb, and will vary quite a bit.
      "Manifold" vacuum is going to be below the throttle plate, or in the intake
      manifold itself, and should be steady. If you have a vehicle with power
      brakes that will generally use a larger hose going right to the intake,
      which will be a fitting that has several vacuum outlets of varying sizes.

      Some of the user-repair manuals I have give a whole page on what sorts of
      things you can figure out about the condition of an engine with a vacuum
      gauge, it's actually quite a useful diagnostic tool.

      > My toyota also had a "economy" light. It always turned red as soon as you
      > depressed the accelerator and the rest of the time it was green. I do not
      > know how it was controlled.

      I would imagine that it was a bicolor LED, but worked pretty much the same
      way as what I'm talking about.

      --
      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 21:32:04 +0200, Roy J. Tellason ... that would be about half a meter, if this is inches of water and not inches of mercury (that s
      Message 2 of 13 , Apr 1, 2006
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        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.
        Actually very similar to the washing machine level sensor i'd say, which
        makes sense considering the size of the membrane seems similar.

        I took one of the water level switches apart, inside is simply a rubber
        membrane with a metal disk attached which presses on a snap-action switch.
        the screw does indeed adjust the force needed, but even on the hardest
        setting it will only be about 0.2 to 0.3 kilos on that membrane, which is
        maybe 25 square centimeters in area, so the sensitivity is pretty high and
        useless for my application.

        I could try to put a large spring in there to make it much harder to
        depress the membrane....


        There are several lots of analog voltage outoput pressure sensors on ebay
        right now, some with 1 athmosphere range, ending tomorrow. Maybe if i can
        get one of them i'd be done. I'd simply put it in a small container
        "reversed" so it measures negative pressure and using the analog voltage
        to switch something should be really easy.

        I also had another idea. if i could get a small pneumatic cylinder i could
        apply the vacuum to one end and a spring to the other end. A microswitch
        could be positioned so that the plunger activates it...

        ST
      • lcdpublishing
        Would this switch work for you? http://www.joewoodworker.com/catalog/product_info.php? cPath=60_36&products_id=58 Chris
        Message 3 of 13 , Apr 1, 2006
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          Would this switch work for you?


          http://www.joewoodworker.com/catalog/product_info.php?
          cPath=60_36&products_id=58


          Chris
        • Stefan Trethan
          On Sat, 01 Apr 2006 22:21:42 +0200, lcdpublishing ... This would probably work, but this is a low/zero budget project. thanks ST
          Message 4 of 13 , Apr 1, 2006
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            On Sat, 01 Apr 2006 22:21:42 +0200, lcdpublishing
            <lcdpublishing@...> wrote:

            > Would this switch work for you?
            >
            >
            >
            > http://www.joewoodworker.com/catalog/product_info.php?
            >
            > cPath=60_36&products_id=58
            >
            >
            >
            > Chris


            This would probably work, but this is a low/zero budget project.

            thanks

            ST
          • lcdpublishing
            Ah yes, I understand those projects :-( Chris
            Message 5 of 13 , Apr 1, 2006
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              Ah yes, I understand those projects :-(

              Chris
            • 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 6 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 7 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 8 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 9 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 10 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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