piping systems. Most valves have moving joints
referring to the List of Materials, you can deter-
between the valve stem and the bonnet. When
fluid is on one or both sides of a moving joint,
Besides the Naval Ship Systems Command
the joint may leak. Sealing the joint prevents this
drawing, most ships have a packing and gasket
leakage. Sealing a moving joint presents a
chart made up specifically for each ship. The ship-
problem because the seal must be tight enough
board chart shows the symbol numbers and the
to prevent leakage, yet loose enough to let the
sizes of packing and gaskets required in the ship's
valve stem turn without binding. Packing is the
piping system, machinery, and hull fittings.
most common method of sealing a moving joint.
PACKING OF MOVING JOINTS
Packing is a sealing method that uses
bulk material (packing) that is reshaped by
Valves are components used to control the
compression to effectively seal a moving joint.
transfer of liquids and gases through fluid
Figure 6-48.--Types of packing.