October 17, 2019 | 1 minute read
When improving the performance of mission-critical pumps, John Crane’s customers face challenges, including high heat generation, poor lubrication, and abrasion and barrier system complexities. To solve these problems, we developed a face treatment, called upstream pumping, as part of our suite of seal face technology options for rotating equipment. Drawing upon our pioneering gas seal innovations in the 1960s and 1970s, John Crane engineered the upstream pumping concept for liquid services and launched this face treatment three decades ago. Today, we answer operators’ toughest challenges, improving seal and pump reliability, preventing unplanned downtime and reducing operating costs across a broad range of process industries.
Why are Face Treatments so Important?
Face material selection is critical to the performance of the mechanical seal. Every mechanical seal application experiences challenges, often including poor lubrication.
Poor lubricating process can damage seal faces leading to increased leakage, unplanned downtime and even catastrophic equipment failure. That’s why our experts have developed a suite of seal face technologies—including upstream pumping—that can address the most difficult sealing problems and optimize the performance of rotating equipment in all process industries.
Starting with Game-changing Technology?
In the 1960s and 1970s, John Crane’s patents for centrifugal compressor mechanical seal designs pioneered the use of non-contacting spiral groove face technology in gas compression applications. These new gas seals revolutionized centrifugal compressor shaft sealing by delivering a step change in compressor reliability and operating costs.
Applying Spiral Groove Technology to Pumps
By the 1980s, John Crane engineers started working with these faces on mechanical seals for pumps, applying that same game-changing innovation to “actively lift” the faces of wet seals. The results were impressive, and the potential for improving pump performance in key process industries was promising. John Crane engineers kept working and launched the T8000 upstream pumping seal in 1989. Now—almost three decades later—John Crane remains the only seal company to offer this innovation for pumps.
How does it Work?
Mechanical seals require a narrow gap between faces to allow a lubricating film to work; the gap must also be optimized to eliminate leakage. The lubricating film thickness is measured in microns. Debris in process fluids can create deposits, damage faces and cause hang-up. Ultimately, seal life is shortened, and the MTBR of the pump is not acceptable. The basic concept of John Crane’s solution is that the conventional seal is replaced by a low-volume, high-pressure “pump”—the upstream pumping seal. This “pump” propels a minute quantity of buffer liquid along the path normally sealed by the mechanical seal faces and into the product side. Because the product side is at a higher pressure than the buffer liquid, this seal is said to pump “upstream.”
Principles of Active Lift Operation Solve the Problem
An upstream pumping seal operates on the principle of hydrostatic and hydrodynamic force balances. The spiral groove pattern serves the purpose of a pressure generating system, directing barrier fluid toward the outside diameter (OD), meeting the resistance of the sealing dam and increasing pressure. This causes the flexibly mounted face to actively “lift,” setting the sealing gap. In this non-contacting mode, liquid is pumped from a low-pressure region to a high-pressure region.
Active lift at a seal interface offers several advantages over the traditional dual-pressurized seal approach:
- The technology is non-contacting and, therefore, the usual pressure velocity (PV) limitations do not apply
- The sealing environment within the seal chamber is cleaner, resulting from positive flow of clean fluid
- Reduced power requirements and environmental contamination
- Self-regulating and tolerant to process pressure variations
- Ability to handle slurries, scaling liquids, abrasives and products with poor lubricity