by Travis Lee, Pulsafeeder, Inc.

Non-metallic magnetic driven gear pump technology improves equipment life and maintenance costs for metering and transfer applications.

Finding an efficient and economically feasible way to transfer and meter aggressive chemicals is a constant challenge in many industries ranging from chemical processing to food and beverage production to municipal water treatment. Limited maintenance resources and critical service demands put a premium on equipment uptime and extending MTBF (mean time between failures).

In metering applications, choices have traditionally included: controlled volume reciprocating diaphragm metering pumps; peristaltic hose pumps; and, for certain applications, even progressive cavity-type pumps. Critical factors for determining which technology to use for a given application include:

  • Material selection/chemical compatibility
  • Accuracy and repeatability requirements
  • Total cost of ownership (TCO)
  • Mean time between failures (MTBF)
  • Ease of maintenance
  • Initial capital cost
  • Installation considerations (footprint, compatibility with existing control schemes, etc.)

With the continued focus on lean operating principles in many industries, the importance of MTBF, ease of maintenance, and TCO continues to play a greater role in the decision of which process technology to use for a given application. A relatively new entrant into the field provides a solution for many applications and meets the expectations of users regarding these key categories. Non-metallic magnetically driven gear pumps are becoming a frequent choice due to their simple operation and maintenance, long term reliability and ability to meet performance requirements.

Non-Metallic Magnetically Driven Gear Pumps

While positive displacement rotary gear pumps have been around for years, the designs featured metallic constructions, which required the use of high-grade alloys (Alloy 20, Hastelloy C, etc.) for aggressive chemical applications. These material requirements required larger capital investments than other technologies chosen for these applications. This has limited the application of rotary gear pumps in chemical metering and transfer applications. However, a completely non-metallic magnetically driven (mag drive) gear pump has been developed that solves many of the critical issues faced in chemical transfer and metering.

Non-metallic mag drive pumps include all wetted parts in non-metallic construction including ETFE housings, PTFE gears, and alumina ceramic shafts. The non-metallic construction extends to the containment can portion of the mag drive. This is critical not only for chemical resistance in harsh environments, but also to eliminate energy loss and heat increase that can be caused by eddy current losses in metallic gear pumps. Bearings are also offered in both carbon graphite and silicon carbide constructions. These material offerings allow the pumps to accommodate almost all the hazardous and classified chemical applications that a plant operator or engineer would encounter. They are also cost effective. A non-metallic mag drive pump can cost up to 30 percent less than a comparable alloy pump and 60 percent less than Hastelloy C.

In addition to material compatibility, the pumps offer sealless mag drive technology. This eliminates the need for a mechanical seal, the potential for leaks and the need for frequent maintenance. This also ensures that no emission issues arise when regulated chemicals are involved.

A Good Choice for Many Applications

Reducing the TCO for process equipment is a priority for most users, and several features of the non-metallic mag drive gear pump assist with this goal. One of the most important considerations for equipment users is MTBF. The overall cost of equipment failures in chemical applications goes far beyond the expense to repair the equipment. It also includes the downtime costs; labor hours required for the repairs; and the potential product loss and safety considerations, especially in aggressive chemical applications. The non-metallic mag drive gear pump allows for extended MTBF in chemical metering applications when compared to other choices.

Peristaltic technology relies upon unpredictable hose/tube life, which may result in frequent replacement. The potential risk of product loss due to “catastrophic failure” of a hose/tube is also eliminated with non-metallic gear pumps. In addition, the sealless mag drive technology eliminates the need for seal maintenance when compared to non-mag drive gear pumps. These savings manifest themselves throughout the life of the equipment.

Another consideration when attempting to reduce TCO is the ease and cost of maintenance. While reducing MTBF is important, so is repair cost reduction when repairs are necessary. In this regard, the non-metallic gear pump provides a unique solution. These pumps contain only 16 wetted components (comparable metallic gear pumps contain 46 components), allowing for quick repair and servicing. All wetted components are easily accessible from the front-pullout design (see Figure 1). This allows the pump to be repaired without disconnecting process piping or removing the pump from its installation location. This saves time and expense.

Front pullout design of the non-metallic mag drive gear pump.
Front pullout design of the non-metallic mag drive gear pump.