All machines such as pumps and compressors that handle liquids or gases must include a reliable means of sealing around their shafts so that the fluid being pumped or compressed does not leak. To accomplish this, the machine design must include a seal located at various points to prevent leakage between the shaft and housing. To provide a full understanding of seal and packing use and performance, this chapter discusses fundamentals, seal design, and installation practices. In addition, shaft seal requirements and two common types of seals, packed stuffing boxes and simple mechanical seals, are also described in this chapter. It also discusses mechanical seal designs. Mechanical seal designs are referred to as friction drives, or single-coil spring seals and positive drives. Single-coil spring seal design is limited in its use to liquids such as water or other nonlubricating fluids, because the seal relies on friction to turn the rotary unit. If this type of seal is to be used with liquids that have natural lubricating properties, it must be mechanically locked to the drive shaft.