Why seal-less pumps can provide benefits over sealed pumps

The inherent irony that is at the root of many industrial manufacturing processes is this: oftentimes, “bad” things are needed to produce “good” things. Or, to be a little more specific, hazardous things are needed to manufacture useful things. Manufacturers who produce chemical-based compounds such as caustics, acids, solvents and polymers should be well aware of this dichotomy.

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Hazardous substances like toluene, xylene and ethylene oxide — along with a host of hundreds of others — that can be harmful to humans and the environment if mishandled are nevertheless indispensable components that must be used in a large number of industries and end products. A tip-of-the-iceberg list of such industries and products includes, but is hardly limited to, petrochemicals, paints and coatings, soap and detergents, biofuels, adhesives, pulp and paper, food processing and herbicides and pesticides. 

In addition to being widely used and potentially dangerous or hazardous if mishandled, many chemical compounds are also extremely expensive. If a leak were to occur during the handling or transfer of these products, large costs would be incurred by the operator through the loss of raw materials, as well as for cleanup and potential environmental remediation. These factors combine to make the full containment of dangerous chemicals a front-of-mind concern for facility operators. 

Pumps are critical pieces of equipment used in the manufacture and handling of dangerous chemicals. They are commonly used to introduce raw materials into the production process or to transfer end products for packaging, storage or shipping to end users. Mechanically sealed pumps have become the accepted technology of choice for these transfer activities. However, this article will attempt to illustrate how seal-less pump technologies can be a more effective choice when full containment of dangerous and valuable chemicals is an absolute must.

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The challenge

When handling dangerous chemicals, there are four main areas of concern that manufacturers must identify and satisfy:

• Safety: Ensuring that site personnel, surrounding communities and the environment are not harmed.
• Product containment: When dangerous or hazardous products are fully contained and not allowed to leak, valuable raw materials and products are not lost to the environment, improving safety overall.
• Maintenance: Mechanical shaft-seal failures are the No. 1 cause of pump downtime in chemical-processing activities. Excessive maintenance costs generally are accumulated in two ways — the need to constantly repair, rebuild or replace underperforming pumps or components, and in the downtime that brings production runs to a halt for several hours or days.
• Operating costs: An overlooked strain on the bottom line can be found in the form of seal-flush water, with the impact of the seal water on the process and the cost of the flush water needing to be taken into account when creating a budget.

The most common pump technologies that are used in the manufacture and handling of dangerous chemicals include diaphragm, sliding vane, lobe, progressive cavity, centrifugal and gear. All of the traditional pump technologies have one thing in common: they rely on various types of mechanical seals or packing rings to prevent shaft leakage. Mechanical seals and packing rings are present in most of the pumps used in hazardous chemical-processing applications, but both have their own potential operational shortcomings:

• Packing rings: This method utilizes braided packing material that includes a set of formed rings that are wrapped around the pump shaft and held in place by an adjustable gland that has been designed to control shaft leakage. To that end, a small amount of leakage is needed for lubrication and cooling, which can be become problematic when handling hazardous chemicals. Therefore, while packing has been widely used in a variety of industries (such as in resin and paint and coatings), it should not be generally considered a best practice for transferring hazardous chemicals.
• Mechanical seals: These seals come in two general variations: single and double. Single mechanical seals can usually adequately address the problem of fluid leakage, but when used with liquids of higher viscosity, the product drag can distort the seal or cause it to break away from the shaft completely. Single mechanical seals also are incapable of containing potentially hazardous vapors. Double mechanical seals can prevent the escape of vapors and are more reliable when handling viscous liquids, but they can be prohibitively expensive to acquire, repair, clean, maintain and replace.

While any of the various types of seals can perform admirably for long periods of time, they will eventually need maintenance or need to be replaced before major shaft leakage can occur. Replacing the seals, not only after they fail but also as a form of preventative maintenance, is costly and will result in downtime that can slow the production process.

The cost of a leak to a manufacturer includes the loss of valuable raw materials or finished products, downtime in production and the costs and potential penalties associated with a chemical-cleanup process. Leaks of hazardous materials that reach the outside environment can be subject to fines and remediation costs from the U.S. Environmental Protection Agency (EPA), as well as other local and state regulatory agencies. Additionally, other countries have their own sets of regulations, which can often me more stringent than those in the U.S. Spilled hazardous materials also pose safety risks for site personnel and cleanup crews, which raises liability issues, while a major leak that can cause damage to the environment can have far-reaching negative effects.

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