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    1991 BMW M3 2.3L FI DOHC 4cyl

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    Honda - Accord Prelude 1996 2000

    Compression Fittings



    The compression fitting has a flared metal tube or a compression fitting that is surrounded by a threaded flare nut. Because the tube is flared or has a compression fitting installed, the threaded flare nut cannot be removed from the line and is considered part of the assembly.

    Compression fittings are most often used when a pressure line attaches to an assembly, much like the fluid lines found at the brake master cylinder or on the inlet fuel line for the firewall-mounted fuel filter found on some Accord and Prelude models.

    The compression fitting does not have a gasket or seal, rather it uses the threaded flare nut to seal the flared end of the line or a compression fitting on the line to the assembly. The flared end of the fuel line or the compression fitting is sealed between the component and the flare nut.

    A compression fitting is most often found where the fluid in the line is under considerable pressure.

    The flare nut is one of two types:

    The externally threaded flare nut: An example of this type of fitting is most easily seen on models where the flare nut is threaded into the brake master cylinder.
    An internally threaded flare nut: This type of fitting uses a compression fitting on the line and the nut threads onto a threaded fitting.

    To disconnect a fuel line using a compression fitting:

    1. Hold the component that the flare nut is threaded onto securely, and using a flare nut type wrench, loosen the flare nut.
    3. Installation is the reverse of the removal procedure.

    Click image to see an enlarged view

    Fig. An example of an internally threaded flare nut on this fuel line. Note the use of a flare nut wrench loosen the nut while the component is held with another wrench

    Click image to see an enlarged view

    Fig. The open-end wrench on the left compared to a flare nut wrench on the right. The slot allows the flare nut wrench to clear the line, yet will grip the flare nut on all 6 sides

    Click image to see an enlarged view

    Fig. An externally threaded flare nut is used on both fuel lines and hydraulic brake lines. A flare nut wrench is shown loosening the flare nut on a hydraulic brake line fitting

    Click image to see an enlarged view

    Fig. The fuel inlet line on a Honda firewall mounted fuel filter is a compression fitting. The flare nut has external threads and is threaded into the bottom of the fuel filter

    Click image to see an enlarged view

    Fig. An exploded view of the Honda firewall mounted fuel filter and mounting bracket. The filter outlet (Top) uses a banjo bolt fitting, the inlet (Bottom) is a compression fitting

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