No such thing as a cheap seal
Life-cycle analysis confirms that “cheap” sealing components are often more expensive in the long run

“Companies who use seals need to get away from the ‘how cheap can you make it?’ approach,” says Rick Page, Director of Marketing at seal manufacturer John Crane. “Many plant construction projects these days are extremely ‘down-and-dirty’, and pumps and seals are some of the worst offenders for cost-cutting. But in the long run, this pressure to buy cheap will backfire on the operating companies and make them uncompetitive in today’s world markets.”

Mechanical seals from reputable companies such as John Crane run anywhere from $2 to $50,000 or more, depending on the application. “Especially when bidding for new construction projects,” Page explains, “there is intense pressure on costs, and not enough emphasis on reliability and energy efficiency. To make matters worse, some seal suppliers encourage the ‘buy cheap’ philosophy by pursuing a lowest-price strategy at the expense of equipment reliability and the end user’s total cost of ownership.”
In the current climate of the relentless pursuit of cost savings, such low prices are bad news for plant reliability and lifetime costs, says Page: “20 years ago engineers and plant managers bought the best technical solutions, with a view to optimizing their plant’s reliability, availability, and safety. These days that is not necessarily the case.”

Convinced that there is a sound economic case for not always buying the cheapest, Page set out to prove it. The key, he says, is to speak the same language as the plant’s managers and accountants. He took his cue from consultant Paul Barringer, an industry expert who has long argued that in order to make a case for change, an engineer must run the numbers and talk in terms of net present
value (NPV). “The use of traditional engineering arguments, and even the concept of payback period, encourages short-termism, now that many of these decisions need approval from upstairs,” says Page. NPV is the preferred language of accountants, and calculated over the whole life of a pump, say 20 years, it
can reveal huge differences in the costs of different sealing options.
From pumps to seals
With the backing of two industry associations, the Fluid Sealing Association and the European Sealing Association, Page set out to create a definitive guide to life-cycle seal costs.
At first, his model was Pump Life Cycle Costs: A Guide to LCC Analysis for Pumping Systems, published by Europump and the Hydraulic Institute. But though this book gives excellent guidance on the principles of life-cycle costing, the FSA soon decided that working engineers needed something more practical and detailed. “Life-cycle cost calculations for seals are actually much more complex than those for pumps, and we wanted a tool that could be used by both beginners and experts,” says Page. “We also needed something that would be accepted as an industry-agreed standard to give it credibility.”
Instead of a book, the FSA decided to produce a computer-based calculation tool that could be used either on the web or offline. John Crane engineer Jason Gondron was enlisted to produce a Microsoft Excel spreadsheet, and the resulting Life Cycle Cost Estimator is now available (see InfoClick-Box).
Though this is by no means the first calculation tool for seal costing, Page believes it is the easiest to use, most comprehensive and most accurate. “Our own in-house costing tool was somewhat clunky and hard to use,” he says, “and I’m sure the same must be true of many other seal suppliers. The FSA’s Life Cycle Cost Estimator is a great improvement, and our salespeople are already using it to support their proposals to customers.”
The spreadsheet can be downloaded for desktop use, but for maximum accessibility it also has a web interface. It allows up to three seal options to be compared side-by-side, and combines simplicity with flexibility. Seal costing involves dozens of parameters, explains Page, that experts can view and modify if they wish. “But engineers whose primary expertise is not seal costing can simply accept most of the default values, which makes the tool very easy to use,” he says. The current version uses imperial units, but the ESA plans to provide a metric version soon. As well as future updates to the spreadsheet itself, the website carries an explanation of all the hidden calculations on which the spreadsheet is based.
Simplicity brings benefits
The main lesson to be learned from
the Life Cycle Cost Estimator is that it is often worth paying more up front to achieve greater reliability, energy efficiency, environmental performance, or all of these.
“There’s an industry saying that you can almost always use a really cheap seal if you back it up with enough secondary equipment—coolers, filters, separators and so on,” says Page. “One effect of accurate life-cycle costing will be to steer users towards sealing solutions that may have higher initial costs, but are able to run with fewer external support systems.”
A classic example of an unnecessarily costly seal system is a conventional single seal with a once-through barrier fluid that dilutes the fluid being pumped. Replacing this with a new double gas seal eliminates the seal fluid, so its higher up-front cost is often justified by greater process reliability and lower maintenance costs. No costing tool can provide all the answers, Page points out: “If you compare three different sealing options, you could find that their lifetime costs come out at $30,000, $40,000 and $150,000 respectively. You might have good reasons for preferring the $40,000 seal over the cheapest option—but at least you know that it’s probably a good idea to reject the $150,000 one.”
If a piece of equipment needs frequent overhauls for reasons other than seal failure, then using a cheap, short-lived seal may be a valid option. “But if seal life is the limiting factor, it’s probably time to choose a seal that’s more reliable, and probably more expensive,” says Page.
One higher-investment option that will not necessarily cost less in the long run, however, is the use of seal-less pumps, which also feature in the Life Cycle Cost Estimator. Seal-less pumps have transmission losses that make them noticeably less energy-efficient than conventional pumps, Page says. They are also more likely than conventional pumps to need returning to the manufacturer for repair, so maintenance and inventory costs are invariably higher.
Finally, any life-cycle cost calculations will only be accurate as long as the seal achieves its expected performance—which means it must be installed and operated correctly. Modern cartridge seals are easy to install correctly, says Page, but they can still be damaged by poor operating practices. “For instance, a large double-ended pump, especially a hot runner, needs several hours’ warm-up before starting,” he says. “Companies who cut corners here can shorten the life of their seals.”