Pressurization leak

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  • #83627

    I seem to get a pressurization leak when the janitrol heater is turned on. A high pitch whistle developes and it seems to start when I turn on the heater. Were are going chasing this week and any tips would be appreciated.

    Thanks

    #95322

    There is a duct in the nose which cracked in my 340 and caused a similar problem with this plane. Using a leaf blower plumbed into the pressurization system as described by Mr. Sexton ,TAS aviation,helped my mechanic solve the problem.

    #95323
    rwelsh
    Participant

      Doug, there are 5 hoses connecting the heater to the defrost system and the cabin; all of which are in a pressure area even though they are in the nose which is unpressurized so they have to be very tight. If they have never been changed, it is a good idea to change them all at one time and it is not a user friendly job. It is possible to purchase the ducts from the vendor Cessna uses. All you need to do is give them the Cessna part number, usually starting with CMXXXXX-X. The company is BEMCO, phone number is 479-795-2121. They usually have a line item minimum of $25.00, but most of the ducts cost more then that. BEMCO’s prices are usually 1/4 of Cessna’s.

      Plan on at least a full day to change all the ducts. When you yake out the old ducts, you will probably find one with a small piece of ducting hanging down which is causing the whistle. You will probably find the defrost ducts in pretty sad shape.

      #95324

      Dick,

      What do you look for to see that the ducts are in poor shape. I have inspected the outside of ducts on our 340, and they seem to be in decent shape. Would I be able to see dry rotting etc. from the outside of the hose?
      I do know our heater was replaced in, I believe, the late 1990’s with a Stewart Warner heater. So I wonder if they replaced them then. I may need to dig into the logs.

      Thanks
      Arie

      #95325

      Thanks for the info!
      We will be looking at this in the near future and will report back on what is found.

      #95327
      rwelsh
      Participant
        quote :

        Dick, What do you look for to see that the ducts are in poor shape. I have inspected the outside of ducts on our 340, and they seem to be in decent shape. Would I be able to see dry rotting etc. from the outside of the hose?
        I do know our heater was replaced in, I believe, the late 1990’s with a Stewart Warner heater. So I wonder if they replaced them then. I may need to dig into the logs. Thanks Arie

        The original ducts to the defroster were a grayish black color with wide spacing on the wires, and they appeared to have more fabric in them then the plastic like stuff we see in current SCAT ducting. These old ducts were the worse and most have been replaced although I found two in mine in 2003 after a depressurization incident got me looking around. The long 4 inch duct that runs from the front of the heater to the front pressure bulkhead “Y” is vunerable because if it is not properly secured with clamps and or tie-wraps it can chafe against the baggage floor and the side. The tricky duct is a short 5 inch one that connects the heater output long duct to the “Y” valve and on into the cabin–a real bear to get out and back on and clamped. It sure would have been much easier to replaced the ducts when the heater was replaced.

        If there is a problem with a duct, it should be visible with the help of a good inspection mirror for teh bottom of the ducts. The ducts that BEMCO makes for Cessna, Boeing, Piper and many others are very durable with excellent materials which is a big step up from some of Cessna’s originals ducts. While you are in the heater area, there is a Service Letter for the heater fuel soleneid that should be accomplished if not already done.

        When I was looking for my pressure leak, I also changed the main landing gear boots as they had some small holes in them from the constant flexing while the gear was moving up and down– this is one bear of a job let me tell you. One experienced mechanic told me to do it myself as he had done a few and didn’t want to again; I agreed with him after I waded through the replacements. The ducts from the sonic venturi to the cabin intercooler have usually been replaced with double cover SCAT ducting which in my plane seemed to hold up just fine although the new ones available are single cover SCAT type. The nice thing about BEMCO’s ducting is it is cut to length and the wire is stopped short so it is easy to install and clamp. Eight years ago, BEMCO also made the landing gear boot seals, but I don’t know if they still do.

        Dick

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