You will use gasket materials to seal fixed joints in steam, water, fuel, air, lube oil, and other piping systems. You will use packing materials to seal joints that slide or rotate under operating con-ditions (moving joints). There are many commer-cial types and forms of packing and gasket material. The Navy has simplified the selection of packing and gasket materials commonly used in naval service. The Naval Sea Systems Com-mand has prepared a packing and gasket chart (Mechanical Standard Drawing B0153). This chart shows the symbol numbers and the recommended

Figure 13-37.-Orifice-type steam trap assembly.

applications of all types and kinds of packing and gasket materials. A copy of the chart should be located in all engineering spaces. A four-digit symbol number identifies each type of packing and gasket. The first digit in-dicates the class of service with respect to fixed and moving joints. For example, if the first digit is 1, it indicates a moving joint (moving rods, shafts, valve stems, and so forth). If the first digit is 2, it indicates a fixed joint (such as a flange or a bonnet). The second digit indicates the material of which the packing or gasket is primarily com-posed. This may be vegetable fiber, rubber, metal, and so on. The third and fourth digits indicate the different styles or forms of the packing or gaskets made from the material. To find the right packing material, check the maintenance require-ment card (MRC) or the NAVSEA packing and gasket chart. The MRC lists the symbol numbers and the size and number or rings required. The NAVSEA packing and gasket chart lists symbol numbers and includes a list of materials. For ad-ditional information concerning packing and gasket material, refer to Naval Ships Technical Manual, chapter 078.