February 4, 2020 | 5 minute read
An important part of fluid-moving rotating equipment, seals keep critical operations running by preventing leaks, containing pressure and stopping fluid contamination.
Nonetheless, mechanical seal problems are one of the main causes of pump downtime.
Mechanical seals often endure tough conditions, including high heat, vibration, pressure excursions, low lubricity, abrasion and intermittent dry running, which can be caused by entrained gasses or incorrect pump operation. Add in volatile organic compounds and contaminated water, and it’s no wonder some seal meantime between repair (MTBR) rates can be measured in just weeks.
However, it may not be incorrect seal selection or improper installation, but that of unavoidable plant operating conditions. These conditions are often unknown, stemming from when the plant was designed, or even unreliable support utilities, such as water, that can result in reduced MTBR.
Improving Seal Life
Understanding readily available seal face technology options that can improve MTBR is good place to start when it comes to improving seal life. Improving seal reliability leads to increased production, and reduced power and water consumption—all of which boost profits for the user.
Choosing the right seal face technology during the specification phase of a new or upgrade project can seem like an imposing task. After all, there are a wide range of design options available. Material selection has changed as well. One of our most recent seal face material innovations, and one of the most effective in demanding conditions, is one of nature’s hardest substance, diamond.
Diamond Face Technology
John Crane Diamond™ face treatments incorporate ultrananocrystalline diamond (UNCD®) technology, where diamond material is grown through a patented chemical vapor deposition process. The technology’s extreme wear capabilities enable treated seals to easily address abrasive or erosive conditions. In addition, UNCD has a low friction coefficient that delivers lower heat generation and energy consumption.
Diamond face technology extends seal life in dry-running and low-lubricity conditions, and improves mechanical pumps and mixer seal performance. Designed for abrasive pumping applications, the technology enhances operational reliability and equipment uptime by reducing wear in abrasive and slurry applications. In addition, the use of this face technology can result in significant energy and water cooling savings.
Upstream Pumping Face Technology
In the realm of seal face technologies, there is also upstream pumping (USP) seal face technology, which borrows from gas seal designs to overcome high-heat, low-lubricity, and intermittent dry-running conditions.
The USP technology is so effective in harsh environments, some applications report an MTBR greater than 10 years. USP can deliver these impressive uptime results because it incorporates spiral grooving on the seal face, delivering the same effect as a pressurized double seal, but without the need for a complex seal support system.
The spiral grooves form the inner portion of one of the seal faces, and as the shaft rotates, clean fluid is actively channeled to the grooves. The groove geometry promotes deliberate fluid flow, creating a localized pressure increase while maintaining superior fluid film support to guarantee face separation. The outer, ungrooved portion of the seal face forms a sealing dam. The pressure differential across this sealing dam, together with the microscopic sealing gap between the seal faces, determines the amount of fluid flow from the low-pressure side of the seal to the process side.
The result is a non-contacting, sealing gap between the seal faces that nearly eliminates wear and extends seal life for years.This face treatment also delivers a simple support system ensuring face lubrication without the cost of a pressurized barrier fluid system.
So the next time you consider replacing the seals in your operation, remember the face treatment options that are available. The right seal face will save you money, time and headaches. Otherwise, an increase in seal inventory and unscheduled downtime for pump repairs may prove to be a costly consequence.
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