Minimum duration between 2 drops

Forums Forum Minimum duration between 2 drops

This topic contains 8 replies, has 2 voices, and was last updated by  Martyn 1 year, 6 months ago.

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  • #1979 Reply

    techcoze

    I have got a local made solenoid valve. Can you please let me know what are following values you get for valves you are using?

    – Minimum drop duration (my valve giving 20ms minimum)
    – minimum duration between 2 drops (my valve giving around 200ms minimum)

    Are above parameters from my valve good enough?

    #1981 Reply

    Martyn
    Keymaster

    Minimum drop size of 20ms is OK but a 200ms delay between drops is probably too long.

    I would suspect, if you can get a drop size of 20ms then the delay between drops should also be about 20ms. How are you testing?

    #1982 Reply

    techcoze

    I tested it yesterday with complete setup including board, flash and camera. My observation was if delay between 2 drops is less, both drops used to mix up in single one. Also many times even while firing single drop, i used to get 2 drops with 20ms size.

    I suspect on following parameters as well
    – water bottle was 40-50cm higher than solenoid valve. I think I also had air leaks in nozzles. (today I will test with bottle and valve at same height with all air leaks sealed)
    – maybe I am using very big / very small nozzle size, today i will try standard 6mm nozzle.

    Do you suspect anything else?

    #1983 Reply

    Martyn
    Keymaster

    The higher you have the water bottle the more pressure on the liquid going through the valve. This is amplified when using large diameter tubing and large nozzles on the valve inlet. I have found that this can help when you want drops to travel horizontally but (imho) it doesn’t really help if the drop is purely vertical (there is a lot of different opinion about this).
    Too much pressure may give 2 drops.

    What opening size does the valve have? The larger the opening the larger the drops will be and the slower it will operate, especially when using higher pressure.

    Make sure you get air tight seals, otherwise you will have leaks and irregular drops.

    Make sure the valve is working well. If the valve is similar to the ones I use you can take them apart and clean the inner parts. Make sure the spring is clean and working well.

    If the valve “clicks” when switched, test it without connecting the water supply, just hold it and listen to the clicks. What is the fastest you can use it and it still clicks.

    #1988 Reply

    Techcoze

    Today I prepared new water bottle without any leaks. Also reduced height difference between valve and water bottle. This solved double drop issue.

    My observation is for same settings (for single drop) drop capture location is not always same. There is always difference of 2-3 cm between consecutive shots of drop. Is this normal or should I expect exact same drop position for consecutive shots? My valve is un branded (not shako or airtek).

    #1989 Reply

    Techcoze

    Also note that I am using TIP122 (and not TIP120) with same run 2.2k resistor as in your original diagram . I hope this should not make any difference.

    #1995 Reply

    Martyn
    Keymaster

    As long as the delay between shots is the same you should get very consistent drops. When photographing just a single drop it should appear in the same place every time.

    Using TIP122’s and 2.2k ohm resistors shouldn’t make too much difference, if any, as the slowest part of the process is the valve. But you can try with a smaller resistor, around 150 ohm, and see what happens. If you don’t have 150 ohm try something similar, like 180, 220, 330, etc.

    If not already, it may be worth while checking the insides of the valves. Make sure the spring is working correctly. I have just added a couple of videos showing the insides of the valves and how to clean them: http://www.dropcontroller.com/solenoid-valves/

    #1997 Reply

    Techcoze

    Opened up valve, everything internally looked clean and ok. No difference after cleanup.

    One thing I noticed is that orifice of my valve is pretty large compared to shako valves. Orifice size is around 4.5 – 5 mm whereas shako orifice is approx 1.5mm (if I am correct).

    Can big orifice be the reason of my problem (double drops + inconsistent drop size, after each drop operation some water is left at nozzle end)? Shall i try reducing orifice size by inserting some plastic refill piece inside it? (without affecting spring plunger functionality)

    #1998 Reply

    Martyn
    Keymaster

    I suspected the problem was a large orifice. They are great for large drops very quickly but not very good for precise drops and fine tuning.

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