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Spooky CNG fillup. CNG leaking from filler nozzle

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  • Spooky CNG fillup. CNG leaking from filler nozzle

    I filled up my 3000 psi vehicle Thursday and there was a stronger than normal CNG smell in the air.
    When I disconnected the filler when it was full like normal I heard a lot of air pressure releasing (fuel)!
    I sort of panicked. It's Never done this before. I thought it was the pump end and was feeling with my fingers but then realized it was my vehicle side leaking. I sort of pressed around my filler nozzle area and the pressure got lighter and lighter and stopped.
    So I started thinking maybe my fill neck's valve is stuck open.
    Maybe it only had like 100-120 psi and leaked that all out to atmosphere?
    Is there a secondary safety valve where the 3000 psi is safely kept behind?
    I checked minutes later and no gas pressure was releasing and also checked an hour later on drive.
    I drove 70 miles on indicated 1/4 tank so tanks arent venting.
    What next?
    will it leak again? Is this really dangerous? Can I replace the fill valve or lubricate it so it doesn't stick open?
    I was pretty scared by that happening suddenly.
    I had filled it up about 6 weeks ago and every fill up before it never did this.
    Last edited by GreenMM; 10-15-2017, 12:04 AM.

  • #2
    Make sure the nozzle and receptacle are clean. Any debris at all can cause the check valve to not close. I had a honey bee (just one leg in the check valve) cause a leak once.

    I spray a little puddle of silicone spray in the nozzle and quickly connect it to the vehicle (put a rag under to catch any drips) and start the pump.That should force some lube into the check valve on the receptacle curing the problem. I do this procedure every couple months.

    The issue may be corrosion from getting wet gas over time and require the replacement of the receptacle or it might be icing that melts away in a short time. Either way, moisture will eventually cause problems in the vehicle system beyond the receptacle check valve..

    If you are using public fueling let the station know that you're getting wet gas. If you are using home fueling add a coalescing gas dryer to the gas line ahead of your compressor.

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    • #3
      I've had a couple of P30 Ford factory receptacles go bad from debris. A Crown Vic somehow got a metal sliver in it and damaged the check valve seal. I had one on a late 90s E series break a check valve spring so it was hit or miss if it sealed properly. Replaced the CV with a new receptacle end, wasn't a stock unit. The E series I replaced the back o-ring face connector with a redundant check valve that is the exact same size as the connector (#6 male o-ring boss to #6 male o-ring face).
      Hopefully you blew out what was keeping it from sealing. In factory Fords, the receptacle is the first check valve. The second (required) check valve is on/in the electronic solenoid valves on each tank.
      So, not to scare you, but if the receptacle check valve fails, you are looking at venting 3,000 psi from the receptacle to all your tank valves and high pressure regulator instead of the space between your check valve and the valve on the filler.
      So instead of a little pssst sound, you'll have a fill nozzle trying to take your hand off and hit you in the chest.
      Ask me how I know...
      If it happens again, I'd suggest replacing your receptacle, or adding a check valve for safety's sake.
      Your Friendly Nazi Squirrel Administrator

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      • #4
        Thanks so much for your answers and tips!!!!
        I have to fill up again tonight and have been worrying.
        I will try a silicone spray.
        And yes I'm only using public unmanned stations for fillups. There's very few options out here.

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        • #5
          I read a few posts searching now on my laptop.
          Can I get an inexpensive Bunin or whatever that strong material is O ring and install a new one?
          How is that done, with fuel still in the system?

          And CNGhal, you had 3600 psi attack you?? Did that all vent out through the nozzle??
          Can that stuff ignite when mixed with oxygen at either the high or very low pressure range?

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          • #6
            ya I went to honda and got the o-ring...had to swap it twice on 2 cars IIRC because the gas will leak as it's filling...scary stuff!

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