Selecting compression packing that is right for your application
Compression packing (sometimes called pump packing) is a sealing material used primarily in pumps to control water leakage along the pump shaft. Compression packing works because the material is flexible enough to be tightened around the pump shaft, thus creating a seal. Selecting compression packing that is appropriate for your particular equipment and application is critical to success.
To perform effectively, the packing must be kept under sufficient pressure to control leakage. In practice, this means that the packing is usually kept tight against the pump shaft, thereby creating friction. The packing must be strong enough to withstand this friction, without breaking down under either the heat or stress created by the rotating shaft. To help preserve the integrity of the packing under these stresses, external lubricants such as grease or water are usually introduced to help dissipate the heat of friction.
Compression packing, sometimes called mechanical packing, is manufactured in a variety of ways: usually by braiding, twisting, or weaving the constituent materials which most often consist of plant, animal, mineral, metal, or synthetic fibers. Most compression packing consists of two elements: the bulk material and an impregnated lubricant. The bulk material is usually manufactured as rope-like material with a square cross-section. The lubricants consist of various greases or oils, both natural and synthetic, such as PTFE or Teflon.
To ensure an optimal seal with compression packing, it is vital to select compression packing that is the right type for the application at hand. The key criteria to be considered when selecting a compression packing include the pump operating pressure, shaft speed, fluid temperature, and the type of fluid being pumped.
As a rough guide, 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. At medium pump pressures of 100 – 150 psi and medium speeds of 1,000 – 2,000 FPM, graphite and acrylic packings impregnated with PTFE and TFE will generally work well, although the temperature of fluid being pumped is also a key consideration. Finally, for high pump pressures above 150 psi and pump speeds greater than 2,000 FPM, metal packing, or packing with metal cores or combinations of metals and synthetics will have to be used. Once again, the temperature of the fluid being pumped is a key determinant of the exact type of packing to be selected.
A good general rule to follow is that the higher the pump shaft speed and the greater the pump operating pressure, the more solid the packing selected needs to be. Choosing the wrong type of packing can result in chronic leaks which results in equipment downtime, increased operating costs, and lost throughput. While compression packing usually represents only a small percentage of a facility’s MRO budget, the increased costs associated with choosing the wrong type of packing can be many orders of magnitude higher than the cost of the packing itself.
At CRGI, we specialize in helping our customers to select compression packing that is optimal for their application. We also carry a full line of compression packings which will service every need. Contact our sales department today for assistance with your compression packing needs.