DIY Vacuum leak detector for less than $20

Discussion in 'Fiberglass and Composite Boat Building' started by MurphyLaw, Jun 25, 2013.

  1. MurphyLaw
    Joined: Aug 2012
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    MurphyLaw Senior Member

    My first infusion repair to the hull of a boat took 2 days to set-up, nearly drove me insane trying to find the leaks. Gave up in the end and just started to infuse with leaks, got very lucky, resin started to gel when it was 20cm from completion, the leak was through the hull so with it gelling so early it sealed the leak itself, didn't even have to close off the feed line, it sealed itself.

    The white areas are fairing compound underneath and not air, I wanted the top layer to be glass and paint only, so I made the hulls true before doing the infusion.

    http://www.boatdesign.net/forums/attachment.php?attachmentid=82145&stc=1&d=1372193425

    http://www.boatdesign.net/forums/attachment.php?attachmentid=82146&stc=1&d=1372193425

    http://www.boatdesign.net/forums/attachment.php?attachmentid=82147&stc=1&d=1372193425

    Second infusion to the other hull(catamaran), was much of the same trying to find leaks, but this time I sealed the hull with a thin layer of Poly Resin before laying out. This time the vacuum pump started up in reverse, I kid you not, after the vacuum had dropped and pumped the bag up till it burst. Luckily it was 2 hours into the cure so everything had already set, and I quickly restarted the pump and resealed all the bagging, and it came out better than the first one.

    Decided I wasn't going to try another infusion until I had a leak detector, couldn't believe they are $250 dollars when the technology they use is less than a transistor radio. Built a couple of prototypes the latest works very well, here's it doing the funky thing on my prototype board.

    http://www.boatdesign.net/forums/attachment.php?attachmentid=82148&stc=1&d=1372193425

    I have just put this design in a box complete with switches and knobs and tested it, leaks sound like a hurricane. Going to use the prototype for a couples of infusions and report back. The parts total for everything, box on/off switch, frequency adjust and volume knobs, and a set off head phones came to less than $20. I think I could get it down to less than $10 but it wouldn't be so sensitive.
     

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  2. groper
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    groper Senior Member

    Brilliant!

    Are you going to post the circuit diagram or are you looking to sell these as a built unit / box?
     
  3. MurphyLaw
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    MurphyLaw Senior Member

    I will post a diagram with build instructions and parts list when I am satisfied that the leak detector can find all types of leaks. I am waiting for an oscilloscope which will take 2 weeks to arrive, I will then fine tune the circuit to be best at detecting vacuum leaks while rejecting other noises.

    I would rather people build their own from parts sourced locally, if I had to ship kits the shipping costs would exceed the build cost.

    If you can glue a boat together then you should be able to glue(solder) a few components together. Not looking to put anyone out of business just help those who are willing to help themselves.
     
  4. groper
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    groper Senior Member

    Thankyou very much, most people willing to give infusion a go, are also the types of people willing to help themselves... So i guess your simply trying to find a frequency range at which vacuum leaks typically operate in?

    The term "ultrasonic leak detector" - to me, seems they might sample in the +20khz range then amplify it and modulate the signal back at a lower, audible frequency to the listener...? Are you going to use the oscilliscope to sample a range of vacuum leaks, deliberately generated by you in a shop environment, to determine the best frequency range for sampling?

    Certainly an improvement on my, "length of hose jammed into my ear" which i currently use. - Youd be surprised at what i can find using this method btw! Heaven forbid if the neighbors saw this strange behavior tho! :D
     
  5. MurphyLaw
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    MurphyLaw Senior Member

    What you really need for leak detection is a spectrum analyser, using your hearing is a bad idea, we are not good at discerning mixed sounds, it's far easier to use our eyes and look at a visualisation of the different individual sounds and their power than try and pick them out with your ears. There are lots of free android apps that are used by car audio enthusiasts that have a spectrum analyser, problem is they only go up to 20Khz and the sound card in your phone or computer start falling off rapidly after 15Khz. What is needed is a little box with a microphone that sends the signal to your Android phone then you could use free sound location apps to locate leaks.

    This project is about building a cheap DIY detector guaranteed to find vacuum leaks, I am going to use the oscilloscope as a spectrum analyser with as many types of vacuum leaks as I can make, then tailor the circuit to be most sensitive to these frequencies. Also the most common frequencies of leaks would determine the length and shape of the detection cone for better sensitivity and direction finding. I am also going to experiment with putting an ultrasound generator in my vacuum tank to see if it sends the sound into the bagging via the pipes and whether it makes leak detection easier. I was thinking of an alarm facility on the detector which if the tank sound is picked up inside the room then the alarm goes off.

    My dog is praying for this project to fail, he can't stand all the ultrasound whistles I am generating with my circuits. I have totally given up on the pipe and ear, if you look at the photos above you can see I used half a roll of bagging tape on that corner trying to fix the leak in my head. I am starting off at infusion repairs on old boats, if the vacuum doesn't hold it's anyone's guess where the problem my lie.
     
  6. MurphyLaw
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    MurphyLaw Senior Member

  7. Psychsurf
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    Psychsurf New Member

    I found this forum and post while searching for this exact sort of thing, a homemade leak detector for my vacuum infusion. I'd love a schematic and parts list if you are ready to share one.
     
  8. MurphyLaw
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    MurphyLaw Senior Member

    I expect to get the oscilloscope by this Friday and then I can tune the circuit more accurately.

    Then I will substitute components that are readily available in all continents.

    Then I will build another unit on veroboard and take pictures step by step and publish including the circuit diagram.

    I'm not publishing the circuit diagram at this time because only a few boat builders would be able to put it together from the circuit diagram and some might be tempted to start selling another $200 leak detector to boat builders which wasn't the purpose of this project.
     
  9. MurphyLaw
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    MurphyLaw Senior Member

    I also won't be putting an ultrasound generator in my vacuum tank as in a vacuum no one can hear you scream. It would have to be the other way around, the generator in the room and the sensor in the tank, and then I am not sure any leak would allow in enough air for the sound to travel in.
     
  10. Psychsurf
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    Psychsurf New Member

    Man, that's great, I really appreciate the effort involved in that and the spirit in which it's done. Have you thought about maybe also posting it up on Make or Instructables to reach a wider audience of DIYers? Thanks again, I'll be watching for the writeup!
     
  11. MurphyLaw
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    MurphyLaw Senior Member

    The prototype Leak Detector is working very well, Have used it on 2 vacuum infusion jobs.

    Time to locate leaks is now less than 5 minutes instead of 5 hours.

    Not sure it needs much tuning, less than $20 and it does the job.

    Very interesting toy, there's a whole unheard world out there, picks up bad connections on electric fences. My boat yard is surrounded by an electric fence, and if you point the leak detector at the fence, it can pick up where dirty connections are.

    Now I must find the time to build and document another unit with instructions etc.

    Is there anyone out there willing to build using my instructions and report back ?

    I have 3 major DIY projects on the go at the moment and have to allocate resources according to demand.

    My oscilloscope arrived but I haven't had time to set-up any experiments to fine tune the detector but the current version is doing the job well so I think I will just publish the instructions and circuit diagram and if more people get involved then any weaknesses will be exposed more efficiently than testing on my own.
     
  12. groper
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    groper Senior Member

    I can build it with your instructions... send me the details and ill make it happen...
     
  13. Psychsurf
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    Psychsurf New Member

    I definitely want to build from your instructions, and I'll be happy to report back with my results. Email me at akshwuz@yahoo.com
     
  14. SamSam
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    SamSam Senior Member

    I'd like to make one also. I think you can send me stuff on the 'private message' feature on this forum.
     

  15. Psychsurf
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    Psychsurf New Member

    Any updates, murphylaw?
     
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