Currently, Canada Rubber group Inc. (CRGI) carries 8 different types of Teadit compression packing in 32 styles. For users, this can present a bewildering array of compression packing types from which to choose. While some types and styles are ideally suited for particular applications, users are still confronted with the problem of choosing the right packing for the right job. This blog attempts to offer some guidance and tips for choosing a compression packing that is job-ready.
Before getting to compression packing selection criteria, a word about when to replace packing. First of all, packing is designed to wear – no packing lasts forever. Some of this deterioration is attributable to the loss of the lubricant impregnated into the packing. While this is normal and to be expected, there are other reasons why packing fails, including the presence of abrasive material, pump conditions including bent and worn shafts, and the improper selection of the type and size of packing material. It is important to note that choosing the right size of compression packing is as important as selecting the right type.
When packing is worn out it must be replaced. A good rule of thumb is that packing needs to be replaced when tightening the packing gland with a wrench will no longer control leakage. Once leakage has begun, and wrench tightening no longer has any effect on the leakage rate, is a sure sign that it is time to replace the packing.
Criteria that should be considered when selecting a compression packing relate to the operating conditions under which the packing will perform. These conditions relate to pump pressures, shaft speed, the temperature of the fluid being pumped, and the type of fluid being pumped. Aggressive media requires a different packing selection than that for more benign media. Concerning pump pressures and speed, a general rule of thumb is that the higher the shaft speed and pressure, the more firm the packing needs to be. The following table provides a rough guide for selecting the right type of compression packing to match your pump operating conditions:
Low pressure (less than 100 psi)**Low speed (1,000 FPM and below)**
Packing made from plant fibers and impregnated with Teflon or PTFE will generally work well at pressures below 100 psi and pump operating speeds of 1,000 FPM or below.
Medium pressure (100 to 150 psi)**Medium speed (1,000 - to 2,000 FPM)**
At medium pump pressures of 100 – 150 psi and medium speeds of 1,000 – 2,000 FPM, graphite and acrylic packing impregnated with PTFE and TFE will generally work well, although the temperature of fluid being pumped is also a key consideration.
High pressure (above 400 psi)**High speed (above 4,000 FPM)**
Choose carbon-based packing, or graphite-based packing with carbon cores. Since higher gland pressures will be required to control leakage, the operating temperature tends to be higher where the packing meets the shaft. Therefore, packing that is designed to work above 850° F should be used.
Concerning selecting the correct packing size, where available, pump manufacturers’ recommendations should always be followed. Where this information is not available, measuring the stuffing box with either a dial caliper or snap gauge may be used to determine the size of packing required.
CRGI’s fluid sealing specialist Bill Searle will be pleased to provide further guidance on selecting the right compression packing for your application. Contact Bill directly at firstname.lastname@example.org.