Packing and gasket materials are required to seal joints in steam, water, gas, air, oil, and other lines and to seal connections that slide or rotate under normal operating conditions. There are many types and forms of packing and gasket materials available commercially.

PACKING AND GASKET SELECTION

To simplify the selection of packing and gasket materials commonly used in naval service, the Naval Sea Systems Command has prepared a packing and gasket chart, Mechanical Standard Drawing B-153. It shows the symbol numbers and the recommended applications for all types and kinds of packing and gasket materials.

The symbol number used to identify each type of packing and gasket has a four-digit number. The first digit shows the class of service with respect to fixed and moving joints; the numeral 1 shows a moving joint (moving rods, shafts, valve stems), and the numeral 2 shows a fixed joint (flanges, bonnets). The second digit shows the material of which the packing or gasket is primarily composed-asbestos, vegetable fibre, rubber, metal, and so forth. The third and fourth digits show the different styles or forms of the packing or gasket made from the material.

Practically all shipboard packing and gasket problems can be solved by selection of the correct material from the listings on the packing and gasket chart. The following examples show the kind of information that you can get from the packing and gasket chart.

Suppose you are required to repack and install a valve in a 150-psi seawater service system. Under the subhead Symbols and Specifications for Equipments, Piping and Independent Systems, you find that symbol 1103 indicates a suitable material for repacking the valve. Notice that the first digit is the numeral 1, indicating that the material is for use in a moving joint. Under the List of Materials, you find the packing is asbestos rod, braided.

For installing the valve, you need proper gaskets. By use of the same subhead, you find that symbols 2150, 2151 type II, 2152, and 2290 type II are all suitable for installing the valve. Notice that the first digit is the numeral 2, which indicates that it is designed for fixed joints. Again, by referring to the List of Materials, you can determine the composition of the gasket.

Besides the Naval Ship Systems Command drawing, most ships have a packing and gasket chart made up specifically for each ship. The shipboard chart shows the symbol numbers and the sizes of packing and gaskets required in the ship's piping system, machinery, and hull fittings.

PACKING OF MOVING JOINTS

Valves are components used to control the transfer of liquids and gases through fluid piping systems. Most valves have moving joints between the valve stem and the bonnet. When fluid is on one or both sides of a moving joint, the joint may leak. Sealing the joint prevents this leakage. Sealing a moving joint presents a problem because the seal must be tight enough to prevent leakage, yet loose enough to let the valve stem turn without binding. Packing is the most common method of sealing a moving joint.

Packing is a sealing method that uses bulk material (packing) that is reshaped by compression

Figure 9-61.-Types of packing.

to effectively seal a moving joint. Figure 9-61 shows several types of packing in common use today.

Packing is inserted in STUFFING BOXES that have annular chambers located around valve stems and rotating shafts. The packing material is compressed to the necessary extent and held in place by gland nuts or other devices.

A corrugated ribbon packing has been developed for universal use on valves. This packing comes in four widths (1 inch, 3/4 inch, 1/2 inch, and 1/4 inch) and is easily cut to length, rolled on the valve stem, and pushed into the stuffing box to form a solid, endless packing ring when compressed (fig 9-62) Corrugated ribbon packing is suitable for use in systems of high temperatures (up to 1200F

Figure 9-62.-Corrugated ribbon packing.

and 2000 psi). It is easily removed since it does not harden.