Here’s what you need to know when choosing between mechanical and packing seals
A long, long time ago, many companies didn’t want to use mechanical seals at all. They were difficult to install and you’d need to take apart the equipment. Then the cartridge and split mechanical seals were invented – solving both these issues in one fell swoop. Despite technological innovations like these, some operations have stuck with compression packing out of habit – even when mechanical seals would provide better results and a better return on their investment.
Similarly, some customers will try to make a mechanical seal work for an application where packing makes more sense. In this article, we’ll share information on how to make the best choice between mechanical seals or pump packing based on operational needs, application, and your budget.
When Mechanical Seals Win
Mechanical seals are the clear-cut choice for any type of equipment, application, or condition where leakage is not an option. A mechanical seal eliminates (or drastically reduces) the risk of leakage, essential for operations that have safety or environmental issues associated with the pumped fluid. Packing simply can’t be 100% leak free, and even single mechanical seals run the risk of leaking tiny amounts of harmful vapors. A double mechanical seal is the safest bet for pumped fluid that has safety, health, or environmental risks.
Other advantages of mechanical seals are fewer bearing failures caused by leaking fluid or failed packing, and reduced sleeve damage, which decreases costs from changing or replacing parts when using packing, including bearings and wear rings. Maintenance teams will also prefer mechanical seals as they don’t need to monitor packing to maintain the slow drip required to cool and lubricate the area, and don’t have to keep adjusting or replacing packing. For plant managers, mechanical seals offer:
A mechanical seal, even if more expensive at the outset, will pay off in the long term due to improved reliability and robustness. By choosing the correct seal design and installing the seal correctly to meet the requirements of your operating conditions, a seal investment will pay off for years to come.
Reduced costs from leakage and product loss
Compression packing is not leak-proof, in fact, some leakage is expected, depending on the application and the fluid to be sealed. Packing has a lower lifespan which also increases the risk of leakage due to seal failure, which can be an issue due to the type of fluid or volume of leakage (and the cost of maintenance or cleaning crews to clean up the mess). In most cases, savings in lost product due to leakage outweigh the cost of the mechanical seal. To find out the cost of product loss on a single pump over a year, measure a single pump for a week (including clean up maintenance), multiply to get the yearly cost and then multiply this number for the pumps across your operation. You’ll quickly see that mechanical seals can offer a far greater ROI.
Less cost and effort to remove contamination
Since many applications require that packing includes a flush to cool, the expense of removing the flush water or any possible contamination can be a deciding factor for some applications.
So, when should I use packing?
Packing was traditionally used to stop leakage around the drive shaft of a centrifugal pump. Rings of braided material, usually fibrous, are stuffed into the pump stuffing (or seal chamber) to reduce the pressure in the pump case and decrease the amount of leakage of the pumped fluid that is forced out along the drive shaft. By their very design, packing rings need to be loose enough to release a trickle of liquid during operations allowing flushing to prevent overheating and wear between the packing surface and outer diameter of the drive shaft.
Compression packing is usually the right choice for rotating equipment. It’s also the optimal choice when the shaft needs to be moved axialy, a requirment of many paper refiners.
When you have enough staff for adjustments and repacking, packing is a cheaper method of sealing pumps. Installation is easier and turnaround times can be faster. Inventory and maintenance can also be less complex for a plant-wide solution.
Another instance where packing might be preferred is large slurry pumps. Although mechanical seals provide an excellent seal, the large equipment size, large shaft movements (with large particles impacting the impeller) and abrasive media means most customers will choose to pack their equipment to save on costs.
Today, packings come in a variety of materials, suited for nearly every application. Innovations such as carbon fiber, new and improved lubricants and braiding allows packing to last longer with less adjustments, maintenance, and equipment wear. However, the cost of product loss for some applications mean mechanical seals may be the better choice in the long run.
Confused about whether you need mechanical seals or compression packing? We’d love to help. Give us a call on 1-800-367-4180 (toll-free). We have experts on hand to help you choose, install, maintain, and monitor a variety of equipment. And to answer questions about things you’ve previously tried gone wrong.
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