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.
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| Front pullout design of the non-metallic mag drive gear pump. |
The simplicity and intuitiveness also allows for quicker training of operations and maintenance personnel. The combination of extended MTBF, low-cost maintenance and simple operation ensures a low resource requirement piece of equipment for maintenance and operations departments that are continually asked to operate with fewer resources.
Many users operate multiple chemical dosing and transfer applications on-site and may have to maintain a wide range of spare parts to fit different technology and varying chemical compatibility requirements. With the non-metallic mag drive gear pump, the basic configuration handles the majority of chemical feed applications. This allows the end user to maintain a minimum inventory of spare parts to service chemical feed systems.
Perhaps even more important than the economic factors are the application benefits. These pumps can handle a wide range of process conditions including:
- Differential pressures to 150 deg F psig
- Working pressures to 200 deg F psig
- Temperature range to 200 deg F (with de-rated pressures; 150 deg F at full pressure)
- Flow ranges from 0.1 gpm to 33 gpm
- Viscosities to 10,000 cps
In addition to standard chemical applications, these pumps are an ideal fit for high viscosity applications, such as polymer blending, as the gear pump efficiency improves with higher viscosity fluids.
Metering Applications
The non-metallic mag drive gear pump can be an excellent fit for metering applications. These pumps provide a pulse-less flow which eliminates the need for pulsation dampeners in the system. A metering application with a vector type variable frequency drive for the pump, a flow meter for flow measurement and a PID controller provides a high level of accuracy (less than one percent variation for properly sized flow meter and drive) and performance in metering applications. This type of system also allows for flow verification due to the flow meter, which is not typically available in most other metering applications in which reciprocating or pulsating flows are used. This allows a high level of accuracy and a high level of turndown capacity with flow rate proportional to the rpm of the motor.
This provides a compact metering pump system containing all the functionality required for most systems.
Transfer Applications
With flow rates available up to 33 gpm, this technology can be a good fit for small to mid-sized transfer applications as well as metering applications. The pulse-free flow and ability to handle a wide range of chemical applications with a single configuration makes this type of technology an excellent fit for chemical transfer applications. The pulse-free flow eliminates the need for complicated piping configurations, such as pulsation dampeners, while the transfer application may not require the flow meter and verification required in metering pump systems, which results in a simple and effective transfer system with a low TCO due to MTBF, ease and reduced maintenance costs.
Recommended Applications:
- Sodium hypochlorite
- Hydrofluorosilicic acid (fluoride)
- Polymers
- Ferric chloride
- Ammonia
Pumps & Systems, September 2010
