Fuel return

Discussion in 'Diesel Engines' started by cal_d_44, Aug 11, 2014.

  1. cal_d_44
    Joined: Jul 2008
    Posts: 18
    Likes: 1, Points: 0, Legacy Rep: 35
    Location: Australia

    cal_d_44 Junior Member

    Hi all, refitting my Ketch with a new Nanni 4.50 engine and the fit instructions state that the fuel return should be 'Returned to below the minimum fuel level'. Now I am running a 30ltr day tank and the existing return line finishes just below the top of the main tank (500ltrs) in the keel. So is there any real reason why it should go through the tank to below the minimum fuel level? I would need to cut the top of the tank open and refit a longer tube to facilitate this?

    Cheers

    Cal
     

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  2. baeckmo
    Joined: Jun 2009
    Posts: 1,117
    Likes: 116, Points: 63, Legacy Rep: 1165
    Location: Sweden

    baeckmo Hydrodynamics

    You have two issues here:

    A/ The tank end of the return should always be submerged, particularly if the tank is lower than the engine. If open to air, the line may slowly be drained when there is no flow. Finally, this can lead to the draining of the injection pump itself, with starting problems as a result.

    B/ Depending on the actual design of the injection system, the return flow may, or may not be a considerable share of the total flow. Now if the return leads back to the main tank, you can reduce the operating time on the day tank, since it will be quickly emptied by the return flow to the main tank.

    I would take the return to the day tank and make certain that the end always is submerged. The idea with a day tank is to separate the main supply from the operationally necessary volume for safety and maintenance reasons. Install a closing valve in the return, and make shure it cannot be closed when engine is running.
     
    Last edited: Aug 11, 2014
  3. cal_d_44
    Joined: Jul 2008
    Posts: 18
    Likes: 1, Points: 0, Legacy Rep: 35
    Location: Australia

    cal_d_44 Junior Member

    Thanks baeckmo, it will be a lot easier to take it to the day tank as it is above the engine. I really appreciate the advise.

    Cheers

    Cal
     
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