Latching pneumatic switch - is there such a thing?

Discussion in 'Hardware & DIY' started by teg1203, 26 Jun 2008.

  1. teg1203

    teg1203 Member

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    Hello All, I'm still getting to grips with some hardware to start off pressurised co2 dosing (!) of a tank. I have been playing with a 24VDC solenoid which works fine but gets chuffing hot! It also consumes more current than I think is reasonable (I am both short in stature and mean beyond comprehension). I know I can source more efficient solenoids out but wondered if there was a device which would act in a fashion similar to a latching relay whereby one input sets the relay and one inputs resets it, thus avoiding having a constant voltage applied. Controlling two inputs for on/off would not present a problem.

    Any advice greatly received (except with regard to tightfistedness - my burden and my gift)..... :D
     
  2. TDI-line

    TDI-line Member

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  3. teg1203

    teg1203 Member

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    Thanks for the reply TDI-line.

    It's difficult to tell from the picture but I think the dennerle part is the same as I am currently using but with a different actuation voltage. The problem with these type of "switches" is that they have to be constantly energised - if you think of someone holding open a door with one of those auto-closer things at the top. The poor blighter holding the door opens get tired and uses up energy working against the spring in the closer. This happens with the magnetic solenoid as the valve is normally closed and this is maintained with the use of the spring inside the valve. What I was particulalrly looking for is a switch or valve that has no spring, is not set at any particular position by default and can use two control lines to place it in either of two states via application of a pulsed voltage which can be removed after the valve/switch has actuated - if such a thing exists. I hope that makes sense. :?

    I'm expecting someone to come up with the phrase " it can be done, but it'll cost you!". :)
     
  4. milla

    milla Member

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  5. teg1203

    teg1203 Member

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    £70 - I feel faint. :eek:

    Thanks for the info milla.

    Now I need to find out who supplies Aqua Medic and see if it can be bought elsewhere cheaper (or sell one of the children for medical experiments) :twisted:

    Do you, or anyone else, think that a similar result could be achieved using a different setup?
     
  6. milla

    milla Member

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    No idea, but if you find something let us know.
    May be a good idea checking medical / chemical suppliers as pulse solenoids are used in drip feed systems.
     
  7. Matt Holbrook-Bull

    Matt Holbrook-Bull Founder

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    it would be nice if this type of solenoid was more common place.. they do get very hot and use silly current!!
     
  8. bugs

    bugs Member

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    I had one of the aqua-medic ones and returned it coz it got just as hot as the normal one...
     
  9. teg1203

    teg1203 Member

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    I must admit I don't understand how a pulse operated solenoid can be integrated into a system which maintains the load and holds the device at an "energised" state without pulling current. The only way I can think that it works is that it energises the coil, pulls in the solenoid, senses that this has been done and uses some clever electronics to resist the spring pulling the valve back into the normally closed position. I wouldn't call this a pulse operated valve myself, more like an energy efficient solenoid valve!!

    But.. having looked at another way of doing this the only option is to utilise an electromechanical approach. Using another type of solenoid or small stepper motor (e.g. servo from RC vehicle) to act on a mechanical pneumatic valve. The drawbacks to doing this are:- A - The valve does not have a failsafe for problems such as supply failure or controller problems, if anything goes wrong it will keep piling the CO2 into the planted environment. B - electromechanical combinations are never reliable if made on a budget. Which brings us to C - it is very expensive to make this type of setup from scratch using new parts. :?

    From what I can see it is far more prudent to stick with the existing technology. Incidentally I have recently seen the "Aqua-Medic Shut-Off CO2 Pulse Valve" for £58, which (if it works as well as they say it does) will pay for itself in approx. 4 years. What should be taken into account is (again if the manufacturers claims are correct) that the running cost is a third of the standard solenoid. From my calculations (and they are as rough as the proverbial dog's bottom) the cost of the pulsed solenoid is £5 per year, versus the standard which comes in at around £15. Dont let these figures startle you too much - they are assuming eights hours daily dosing with CO2 i.e. valves on permanently during day and all the calculations have been averaged up.

    Right, now that's all sorted I'm off to sell some crap on ebay to pay for one of those "pulse" solenoids. Caveat Emptor and all that! :)
     
  10. teg1203

    teg1203 Member

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    I was hoping someone with come up with some ingenious method that they had tried and got working but perhaps the only solution is the one offered on the previous post. ;)
     

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