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Purging your CNG tank to Fill Completely

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  • Purging your CNG tank to Fill Completely

    Do you need to purge your tanks before filling to get them to fill up all the way?
    if so, what is the easiest way of doing this?

  • #2
    Re: Purging your CNG tank to Fill Completely

    I guess you could purge a new tank containing air by having the solonoid valve open and vented for a few seconds. Will not accomplish much. It's not like a system where non-condensables screw up the operation.

    Air , natural gas mix pretty well , and the issue of " non-conceables " really is not an issue because everything except compressor oil is in a gas state. Not much , if any oil should be in the tank anyway.

    What is the "water capacity" of the tank and how much cng are you able to get in it at 3000# or 3600#
    Last edited by Lakewood90712; 07-23-2011, 06:52 AM.


    • #3
      Re: Purging your CNG tank to Fill Completely

      I have two tanks, right now they are single and not connected together.
      each are 100 Liters
      last night i was able to fill the first one to about 6 gallons.
      the other one to 4 gallons.

      although the filling station is kind of tricky, as the first time i went it filled 1.5 gallons and wouldn't put after that. I then re-ran my credit card about 5 times with nothing pumping after that.

      this time, i ran my credit card and the first activation it didn't pump anything, i re-ran my card and it actually pumped 6 gallons into one tank until i temporary shut it off to disconnect and connect to the other tank, it wouldn't pump anymore, have to re-run my credit card and it pumped 4 gallons.

      this is all done on 3000psi


      • #4
        Re: Purging your CNG tank to Fill Completely

        6 gge from a 3,000# fast fill is about all you will get in a 100L tank. The most I have gotten in a 100L "empty" tank with 3600# fast fill is about 7.25 gge. Did you try the second tank right after ? , if it is a very small station , you might be already drawing down the station pressure. Does the station have a dial pressure gauge ?


        • #5
          Re: Purging your CNG tank to Fill Completely

          No, you don't need to 'purge' your tanks to get 'full' fills. The pressure at the dispenser you were using was probably low when you got little or nothing. Once you fill a tank, the trick is to wait for it to cool and then you can usually get a little more in there. Most dispensers will not give you the full pressure below a certain temperature (to allow for expansion with rising temperature) and at higher temperatures there will also be less gas delivered to a given size tank at a given pressure. But the bottom line is that it all depends on what ACTUAL pressure the dispenser is delivering, not what's left in your tank.
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