Paul Cardon is the industrial products manager for Auxerre, France-based Mouvex
On the other hand, sliding vane pumps operate through the use of a number of vanes that are free to slide in or out of slots in the pump rotor when it is driven by the pump driver. The turning of the pump forces the vanes to move outward and ride against the inner bore of the pump casing, which forms pumping chambers in the process. As the rotor revolves, the fluid enters the pumping chambers from the suction port. The fluid is transported around the pump casing until it reaches the discharge port, where it is forced out into the discharge piping.
This design guarantees fixed displacement volume with minimal pressure variance, meaning that energy-wasting slippage and turbulence are minimized and high volumetric efficiency is maintained.
Pump-shaft sealing has traditionally been a problematic factor in sliding vane pump technology. Though often ignored, pump-shaft sealing can directly influence a pump's power consumption in a variety of ways:
- By its basic design, the more friction a pump generates, the more of a "power eater" it will be. From that standpoint, shaft packing is a less-efficient solution.
- In many cases, a pump's shaft-sealing system may need additional cooling, either by a separate fluid (a mechanical seal flush, for instance) or by diverting part of the pumped liquid flow (magnetic drive). This additional cooling requires more energy to work and decreases the pump's energy efficiency.
- Most of the shaft-sealing solutions are heat generators and can dry-run for only short periods of time, or even not at all. When choosing a pump-shaft seal, this parameter must be mastered, especially in a potentially explosive atmosphere. Therefore, temperature sensors, flowmeters and power monitoring often have to be added, which generate other energy-consumption concerns.
When shaft packing or a basic mechanical seal cannot be used in a pump's design, the main alternatives are a double-flushed mechanical seal, magnetic drive and sealless drive.
Seal of Approval
A line of sliding vane pumps now exist that are not based on magnetic drive, but on a sealless leak-free design that features no magnets, mechanical seals or packing.
Instead of magnets, the pumps have a double stainless-steel bellows that houses an eccentric shaft. This shaft, which a crank system rotates, drives the bellows in a circular movement. This design and operation addresses each of the concerns of shaft-sealing mentioned above:
- The sealless drive is needle/roller-bearing mounted with separate sources of lubrication, meaning that frictions are reduced to a minimum.
- The pump's entire flow rate crosses the sealless drive chamber, meaning that the shaft does not need any additional cooling, while none of the flow rate is diverted.
- In most cases, power monitoring is not necessary. An optional temperature sensor can be added in extreme cases.
On the sealless drive vane pump, the bellows houses an eccentric shaft. This shaft, which a crank system rotates, drives the bellows in a circular movement.
The result is a decrease in energy consumption with a corresponding increase in operational efficiency, all without added installation complexity. Compared to magnetic drive pumps, these pumps create up to a 40 percent reduction in absorbed power and up to a 20 percent higher return in energy efficiency.
Sliding vane technology is used worldwide to reduce energy cost and consumption, and create a more efficient pumping system. Sliding vane technology has been taken to the next level with the introduction of sealless drive technology.
Pumps and Systems, July 2010