Installing compression packing correctly for a leak-free seal
Selecting the right compression packing for your application, while important, is only half the story. Installing compression packing correctly is equally important to achieving a leak-free seal. The correct installation of the packing cannot be over-emphasized - many packing failures are due to incorrect installation of the packing.
The procedure for correctly installing compression packing in both pumps and valves is well-known and is routinely published by both pump and packing manufacturers. However, here are some tips to be aware of that help ensure a successful seal every time.
First, before commencing any installation, ensure that you have the right packing available for the job at hand. While there are multiple factors to consider when selecting packing material, a critical factor is the shaft speed of the pump. Charts are available which show the pump shaft speed as a function of the shaft diameter. Use a reference chart to ensure to calculate your pump shaft speed and help select the right packing for your application.
When removing the old packing from a pump or valve, always inspect the pump or valve shaft for wear and tear. Even with new packing installed, a shaft that is excessively worn, scored or grooved may continue to leak.
It is also important to take care when cutting packing into rings for installation. A common error is to inadvertently stretch the packing excessively when cutting. Stretching the packing can affect its performance once installed. Also, ensure that the packing is kept clean and free of contamination from dirt and grime when cutting. Contaminated packing can introduce wear and tear on shafts and cause reduced performance once installed.
Another mistake that is often made when installing pump packing is to jam the packing by over-tightening the gland nuts. Rather, gland nuts should be finger-tightened at first, prior to pump start-up. At pump start-up, the packing should leak freely, with the gland nuts then being gradually tightened over the next 24-hours to achieve the desired leakage rate.
Attempting to stop leakage by over-tightening the gland nuts prior to pump start-up will only exacerbate the problem and cause the newly installed packing to burn up. The same problems can occur when installing valve packing if the valve stem is over-tightened. It is important never to over-tighten a valve stem to the point where it cannot be turned. Rather, the valve stem should be free to turn after new packing is installed, and then fully tightened after a 24-hour period, even if no leakage has occurred.
Finally, it should be noted that the manner in which compression packing is stored can affect its performance in use. While compression packing generally has a long shelf life, storing packing in conditions of high heat can dry out the lubricant impregnating the packing. Packing that has dried out should always be discarded and never used.
If you follow these tips along with the correct installation procedure, your next packing change should go smoothly, with minimal downtime and leakage!
Bill Searle welcomes comments or questions on any aspect of this blog post. Contact Bill directly at firstname.lastname@example.org.
 Procedures for installing compression packing in both pumps and valves have been published by both Flowserve Corporation and Garlock Sealing Technologies Inc., among others. They can be found at the following links: http://www.flowserve.com/files/Files/ProductLiterature/Seals/fis107_packing_install.pdf; www.garlock.com/download.php?obj_id=1123; www.garlock.com/download.php?obj_id=1124.