53-10-01 CURTISS-WRIGHT: Applies to all C-46 Series aircraft.
To be accomplished not later than November 1, 1953.
To guard against the possibility of excessive air temperatures and associated fire hazards in the vacuum system discharge line, one of the following modifications must be accomplished:
1. Install a fusible plug in the side of the vacuum pump discharge port at right angles to the axis of the discharge port boss. Some pumps incorporate a plugged hole in the discharge port which may be enlarged to a 3/8-inch pipe tapped hole to accommodate the fusible plug. This plug should employ an AN 840-8D fitting with a binary eutectic mixture of 67.8 percent tin and 32.2 percent cadmium, which has a melting point of 351 degrees F. A drawing describing the design of such a plug is shown in Figure Douglas 2. The 3/8-inch fusible plug fitting is intended for pumps such as the Model 3P-211. Brass fittings of the same design as the above dural fittings are also acceptable. Incorporation of an overboard drain line clamped to the fusible plug is recommended, but is not mandatory. On installations which do not use an overboard discharge line the possibility exists that the plug may damage other nacelle components if it can hit them upon being blown out of the adapter at high velocity. Therefore, if no overboard discharge line is provided, the installation must be made in such a manner that the plug will not be directed toward any vulnerable components when it is blown from the adapter.
Also, incorporation of steel lines with fire resistant hoses and utilizing hose liners and clamps in the vacuum discharge line is recommended if cracking and drying out of the flexible hose assemblies is experienced.
In lieu of this fusible plug installation:
2. An oil separator equivalent in principle to the Genisco No. 40081 incorporating a pressure relief valve which can be disassembled for cleaning must be provided. (Genisco Co. is located at 2233 Federal Ave., Los Angeles 64, Calif.)