The correct load for the packing had to be determined using a combination of experience and experimentation. The live-load assembly was designed for a range of loads, with its mid-compression point the target load. The available travel was set at the maximum possible. This may have resulted in a larger, more expensive live-load arrangement than would be found on a typical gate or globe valve, but the user was clear that this solution had to provide four and a half years of leak-free service.
An installation procedure was developed to apply the gland bolt torque in increments, starting with the minimum value designed for the assembly. The valve was pressurized and checked for operability and leakage. If any leakage was detected, the gland bolt torque was increased slightly, and the test was repeated until the seal was achieved and the disc was still free to move as required. To date, the application has been running for three, leak-free years.
For difficult applications with special challenges, collaboration can be important. In this case, an end user’s experience and understanding of the application history and challenges and the compression packing supplier’s knowledge and experience with sealing options resulted in a successful, unusual sealing solution. Communication and open discussion are critical. Each party’s expectations were clearly laid out before any specifications were drafted or purchases made. If end users have a challenging sealing problem, they should contact and collaborate with their sealing solution provider. P&S
Next Month: How does lubrication affect fastener torque & resultant tension?
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