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Seal-less Pumps Provide Leak-Free Resin Handling

Contributed by: Dale Evers at EnviroGear

Pumping Industrial Resins
Manufacturing, handling, and transporting

Resins are integral to paint and plastic production. An all-encompassing term, ‘resin’ includes thermoplastic, thermosetting, engineered resins, and thermoplastic elastomers. Because resins are often customized by adding fillers, catalysts, and modifiers, they have a wide range of uses and reliability. Unfortunately, this high level of customization also means resins are difficult to transfer due to heat and/or shear sensitivity that varies from one formulation to the next.

Selecting the proper pump for these applications requires a review of the suction and discharge piping system, operation duty cycles, and flushing procedures, in addition to an examination of operating and maintenance costs. The largest concern in pump selection for resin applications, however, is that of shaft leakage. Traditionally, seal-less internal gear pumps were not considered effective for solving the problem of leakage. Recent developments, however, may prove that seal-less pumps are not only effective, but also a more cost-efficient and environmentally friendly option for resin-handling applications than traditional mechanical seal pump types.

The Sealing Situation

Historical sealing strategies, shaft leakage, seal-less stigma

Positive displacement rotary gear pumps are a top choice for resin-handling applications, but the issue of shaft leakage remains a primary concern. Several sealing techniques have been implemented in an attempt to solve this issue. Below is a brief overview of these techniques, some of which are no longer accepted technologies:

Packing - Although no longer an accepted solution in most resin-manufacturing applications, packing was widely recommended for many years. This method relies on braided packing material that includes a set of formed rings wrapped around the pump shaft and held in place by an adjustable gland that controls product leakage. Issues with over-tightened glands could restrict product flow and damage the pump shaft, which is why this method is not accepted in most resin-manufacturing plants today.

Multiple Lip Cartridge Seals - This design relies on an elastomeric lip with an inner-lip diameter that is slightly smaller than the pump shaft diameter. Each lip is energized or loaded to a precise radial force between the lip and the shaft. Over time, the inner lip wears, as does the pump shaft/sleeve surface, which can lead to a catastrophic failure without close monitoring and maintenance.

Mechanical Seals - Mechanical seals come in two variations: single mechanical seals and double mechanical seals (dual-pressurized). The former are rarely used for resin-transfer today because viscous drag can cause the seal to distort or break free from the shaft completely. While single mechanical seals address the problem of fluid leakage, they do not contain vapors. Double seals can prevent process vapor loss with proper maintenance and are more suited for viscous applications. In this design, all four sealing faces operate within a pressurized barrier- fluid system. Extra protection comes at a high cost, however, in both up-front cost, maintenance, and repair.

Historically, seal-less pumps weren’t considered a good alternative. Due to recent technological developments however, past operational concerns regarding seal-less internal gear pumps for some resin applications are no longer an issue. While careful consideration of the pumping application and all aspects of operation are still paramount to proper pump selection, seal-less pumps can offer users a less expensive and more environmentally friendly solution.

Magnetically Driven Seal-Less Pumps
Advantages, applications, and limitations

Magnetically driven seal-less pumps are leak-proof by design because they are not coupled directly to a motor. Certain manufacturers also implement unique design features specifically for resin-handling applications, such as EnviroGear’s patented “between-the-bearing” support system. This system eliminates the cantilevered-load issues so common in other types of positive displacement pumps by supporting the rotor and idler gears at three locations.

Cost and Maintenance Information

In most cases, seal-less internal gear pumps are competitively priced when compared to double-sealed pumps and priced below traditional magnetically sealed pumps. Initial costs are only one consideration, however. The Hydraulic Institute reports that up to 50% of the total cost of a pump is spent on maintenance issues. Because seal-less pumps are relatively easy to maintain, total cost over the life of the pump is very affordable. EnviroGear seal-less internal gear pumps are designed with only seven main parts which are easily serviceable in the field or can be replaced with same-day delivery. EnviroGear seal-less pump parts are also interchangeable dimensionally and hydraulically with many brands of mechanically sealed pumps, making an upgrade relatively painless and inexpensive.

When are they the right choice?

Although seal-less internal gear pumps may work well for many resin-handling applications, there are certain situations where they are not the right option. Seal-less internal gear pumps cannot handle resins that contain heat-sensitive materials or highly abrasive fillers. They should also not run dry for extended periods of time, though the same could be said for mechanically sealed pumps. If running dry, deadheading, or lockups are a concern, the user should consider investing in a power-monitoring device or installing a temperature monitor within the pump.

Read the original article on PSG.