Pressure test fuel filter for leaks?

Discussion in 'Downeast Engine Room' started by OLD BAY, Jul 10, 2018.

  1. OLD BAY

    OLD BAY Captain

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    Cummins 330B mechanical engine:

    I have an air leak in my fuel system I’ve been chasing down for ages. Using clear hose (temp only, used at the dock) I’ve tracked it down to my primary (NOT the last chance on engine) fuel filters set up. My primaries are a dual head spin on type (ff5013 then fs1001, the SMX double double set up). I’ve tried changing the filter canisters, but the leak persists. It’s not horrible, the engine never shuts down, but she does stumble after idling for extended periods as she clears the air. At 1900 RPM I can easily see the pea sized bubbles every few seconds in the clear tube after the fuel leaves the primary filters, vacuum is about 3”.

    Rather than disassembling my primary filter system (there are about a dozen connections, with valves and the 2 filter heads), can I hook up a pump and pressurize the filters and engine lines? I can close off the tank side but I can’t easily close off the engine side. Will pressurizing the lines harm the engine/lift pump?

    Thanks in advance.
     
  2. Keelboater

    Keelboater Captain

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    Although adding pressure to the supply line improves the net positive suction head available to deliver fuel, it is not a good idea to go this route. If the pressure becomes too great, that air leak will evolve into a fuel leak. These filters are designed to run on a vacuum.
     
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  3. Diesel Jerry

    Diesel Jerry Captain

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    Can you send a pic of it to my email? Maybe post it as well.
     
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  4. OLD BAY

    OLD BAY Captain

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    I meant just statically adding pressure, just to find the leak. Not while the engine was running. I was hoping that fuel might seep out under static pressure at the same point air gets sucked in while running. Does that make more sense? If still a bad idea, I was thinking i could pull the primaries and bench test the set up under pressure. It’s just a pain to do that.
     
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  5. OLD BAY

    OLD BAY Captain

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    Thanks Jerry. I work late tonight but will get a pic when I get home and there’s daylight. I appreciate the help.
     
  6. WoundUpMarine

    WoundUpMarine Captain

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    I’ve been having the same issue, pulling slight air into the system and seeing it in the racor. I took the check ball out of the racor and capped my fuel suctions at the tank and pressure tested everything to 20psi, and found no leaks, so pressure testing doesn’t always work.
     
  7. OLD BAY

    OLD BAY Captain

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    Bummer that’s good to know though. Pressure testing is my last option short of disassembly.
     
  8. WoundUpMarine

    WoundUpMarine Captain

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    Yeah sometimes leaks can suck air in and seal when pressurized the other way, it was definitely a bummer not to find my leak.
     
  9. traditions

    traditions Captain

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    Do you have a Racor with the drain that is glued in? I have seen them leak air, but you can usually see it in the bowl. Always get the Racor with the heat shield, or change the bowl to the one with the threaded drain. The glue doesn't hold up well when you are using the drain.
     
  10. Tunatown

    Tunatown Senior Member

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    Wound up have you checked your pick up tubes for pin holes?
     
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  11. OLD BAY

    OLD BAY Captain

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    Here are a few photos of my set up. Space is tight.

    [​IMG]

    [​IMG]
     
  12. Tunatown

    Tunatown Senior Member

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    Old bay did you install The barbed fittings on the smx setup fuel in and fuel out if so what did you seal them with?
     
  13. Diesel Jerry

    Diesel Jerry Captain

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    Along with the email I sent you last night check the surface where the gasket meets the filter head. Maybe a little metal burr there.
     
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  14. OLD BAY

    OLD BAY Captain

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    Thank you Jerry. I will look at the filter head mating surface more closely. I wonder if I’ve installed the filter canisters too tight. I unscrewed the filter and it was on super tight. I almost couldn’t get it off with a filter wrench. And the rubber gasket was not uniformly seated, it had waves in it like it was distorted.
     
  15. OLD BAY

    OLD BAY Captain

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    Thank you Tunatown. I did install the barbed fittings on the SMX setup. I used loctite 567 pipe sealant, which floscan recommended. The fuel hoses are fitted dry and double clamped.
     
  16. BillD

    BillD Captain

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    I had the same Double/Double SMX setup on the twin 370s in the Blackfin and now just a single SMX FS1000 in the 25 T Jason with the 370. Never had a problem.

    I just changed the FS1000 this past Saturday.

    Each Fleetguard cannister filter comes with a new donut gasket. I've seen round donut gaskets and ribbon donut gaskets come with the new filters.

    Important: the old donut filter does not always come off the thread post when you unscrew the old filter.
    Easy enough to make the mistake off slipping on an additional gasket that comes with the filter with the old one still in place.

    Question/s ??

    1. Is the SMX double/double filter head a "new install" and leaking air from the get go ? Or a new occurrence?
    2. Have you double checked to make sure the the round donut gasket is on the thread stud of the SMX filter head?....and that the gasket doesn't have a tear.
    3. And double checked to make sure there are not "two" donut gaskets jammed up on the thread post?
    4. What did you use for thread goop (answered above) when you assembled the NPT fittings into the filter head?
    5. You could have a fuel hose connection on one of the NPTs sucking some air or one of the threads.


    You could post the same question/issue over on Seaboard's Community forward.
    Forums - Cummins Marine Forum

    Best I can do with suggestions without a "look"

    Keep us posted.
     
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  17. Bill_N

    Bill_N Captain

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    Did you put oil or grease on the rubber gasket face? Also, can you tell if the threaded stem is square to the sealing face? If you put some new cannisters on look to see if the gap between the cannister gasket and sealing face is consistent around the circumference. If it's way off that might be the issue.
     
  18. OLD BAY

    OLD BAY Captain

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    Thank you Bill. This is really helpful. The SMX is new (as of last year) and I have had the leak since install. I know it is something I did on install, not the set up itself, which is a VAST improvement over the racor it replaced. I’ll check the gaskets again. I think it’s leaking at the gasket site, but it certainly could be a npt fitting. I’ll start with the gaskets again and go from there. I still wonder if I’m over tightening the filters.
     
  19. OLD BAY

    OLD BAY Captain

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    Thanks Bill, that’s a great idea and I will absolutely look to see whether the threaded stem is square. I do put grease on the gasket, both faces.
     
  20. mike@mpi

    mike@mpi Senior Member

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    Here is how we checked for suction leaks which generally showed up as hard starts after sitting or an unstable idle . Fill the tanks with fuel to minimize air space and run the engine to fill the fuel lines and filters. Shut down and take a radiator pressure tester or other low pressure pump and then pressure test the fuel system by connecting through the fuel tank vent. Use a gauge, that's super important, no more than 3 psi, that's the most tanks are equipped to take and let it sit an hour or so, then see where fuel is escaping the lines, connections or filters. That's where your suction leak is at.
     
    Last edited: Jul 11, 2018
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