by Ted Ratcliff
December 17, 2011

The Solution

Through the years, many pump technologies have been used in the effort to optimize liquid transfer from ship, barge, railcar or tank truck into storage terminals. The one pump technology that has repeatedly been proven the most effective in this application—for all the many products that are handled in this fashion—is the positive displacement sliding vane pump.

Sliding vane technology was invented in 1899 by Robert Blackmer as an alternative to the inefficient gear-type pumps that dominated the market at the time. Because of the nature of their operation, the flow rate and efficiency of gear pumps will erode over time as the pump's gear teeth wear. On the other hand, sliding vane pumps feature vanes that slide out of the pump rotor as they wear, meaning there is no drop in flow rate and volumetric efficiency as the pump ages. Realizing that he had found the solution to the liquid handling needs of a wide variety of industries, he incorporated his company in 1903.

Sliding vane pumps contain a series of vanes that freely slide into or out of slots in the pump rotor. The pump's rotation draws liquid in behind each vane, through the inlet port and into the pumping chamber. As the rotor turns, the liquid is transferred between the vanes to the outlet where it is discharged. Each vane provides a positive mechanical and hydraulic displacement of the liquid.

The vanes are actuated by three forces:

  • Centrifugal force from the rotor's rotation
  • Push rods that move between opposing pairs of vanes
  • The liquid pressure that enters through the vane slots and acts on the bottom of the vanes

Therefore, each revolution of a sliding vane pump displaces a constant volume of fluid with variances in pressure having a minimal effect. This minimizes energy-wasting turbulence and slippage, while the pump's high volumetric efficiency is maintained.

Further since the vanes constantly adjust to accommodate for wear, the pumps maintain near-original and consistent volumetric performance over time. A key consideration for the liquid-terminal storage industry is that sliding vane pumps are able to create a tremendous amount of dry suction.

This suction capability results in a pump that can most effectively strip pipes and hoses while removing as much of the heel as possible from barges, railcars and tanker trucks. Also, the ability of a vane pump to move air allows it to “blow down” the discharge lines. The operational ability of sliding vane pumps also makes them the ideal solution for transferring highly viscous liquids.

Realizing the growth in green operations and the increased concern for the environment, some companies design pumps and compressors to be energy efficient. This enables pump users to gain a competitive business advantage through the deployment of energy-saving positive displacement sliding vane pump technology.

Conclusion

The liquid-terminal industry is one of the most crucial in the world. Every day, millions of gallons of raw materials and finished products in a wide array of industries are transferred into and out of liquid terminals around the globe via delivery vessels. The terminal operator has a large number of challenges:

  • Ensure that the product is loaded and unloaded safely, for both terminal personnel and the environment
  • Enable the product to be transferred in the most energy- and time-efficient manner possible
  • Remove as much of the heel from the barge, railcar or truck as possible
  • Guarantee that no product cross-contamination occurs
  • Perform these tasks in an environmentally-friendly way

For more than 100 years, positive displacement sliding vane pump technology has met these parameters. That is why more savvy terminal operators are turning to sliding vane pumps as the solution to the product transfer needs of their liquid-storage terminals.

Pumps & Systems, April 2011

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