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Why doesn't it work with "gravity fed systems"

  • eugbug1 Sunday, November 24, 2013 6:10 PM Reply
    Is this something to do with the minimum pressure the valve can cope with?
    Eugene's Arduino Blog

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  • ebpDoug Sunday, November 24, 2013 6:54 PM Reply
    Yes, they require a certain minimum pressure to operate.
    These are what is known as "pilot operated" valves. The solenoid directly controls only a very small orifice. This allows low coil power, and in some cases magnetically-latching solenoids. Flow through the tiny orifice allows the main diaphragm for the large orifice to open, but there must be some pressure to make this happen. For water, pilot operated valves typically open and close quite slowly, which is a big advantage in preventing "water hammer" but makes them unsuitable for some applications.
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    post edited by ebpDoug on 11/29/2013 at 6:39 AM
  • harvie Wednesday, October 01, 2014 11:23 AM Reply
    ebpDoug is true. Difference between input and output should be at least 0.2 bar. I am going to use this valve for low pressure CO2 gas in my MIG welder, so i hope it will be enough.

    It will probably work with gravity fed system until your vessel's water level will get low enough. Then it will drain it completely as water level will not be high enough to cause the needed pressure of 0.2bar... Unfortunatelly 0.2bar means that you will need approximately 2 meters of water above the valve. So you can eg. put vessel on the roof and use valve downstairs. Even tap water works like that: http://en.wikipedia.org/wiki/Water_tower

    Also there is one-way valve at the output of this valve, so be carefull to hook it right way. I am going to put this valve away as it causes little fart-like noise when used with gas (well maybe there is some water left...) and also makes pressure difference acros the valve bit smaller. You can try removing it too if you have troubles with low inlet pressure, however you have to be sure that there will never be any pressure from oposite direction (which will almost certainly be there if you use water or have some kind of hoses/jets after the valve, so be careful).
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