by Tom Stone
February 24, 2010

The Sliding-Vane Principle

Blackmer founder Robert Blackmer invented the sliding-vane principle in 1899 as an alternative to the inefficient gear-type pumps that dominated the market at the time. Just by the nature of their operation, a gear pump's flow rate will gradually decay 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, and when the vanes do reach the end of their useful life, they are easily replaced.

Specifically, sliding-vane pumps have a series of vanes that freely slide in or out of slots in the pump rotor (Figure 1). 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. Vanes are actuated by three forces: (1) centrifugal force from the rotor's rotation, (2) push rods moving between opposing pairs of vanes and (3) liquid pressure entering through vane slots and acting on the rear of the vanes.

Therefore, each revolution of a sliding-vane pump displaces a constant fluid volume with variances in pressure having minimal effect. Energy-wasting turbulence and slippage are minimized, and high volumetric efficiency is maintained. Since the vanes constantly adjust to accommodate for wear, unlike gear pumps that are not self-adjusting, sliding vane pumps maintain near-original and consistent volumetric performance over time. Sliding vane pumps also provide a tremendous amount of suction. This suction capability can benefit terminal operators by stripping lines and removing "heel" from tankers.

Because of the design of the pump's rotor and independent sliding vanes, sliding-vane pumps are easy to maintain at peak performance levels and, if necessary, can be completely rebuilt with the piping still attached. In the event the vanes become worn to the point where they need to be replaced, this can be accomplished by simply removing the outboard head assembly, sliding out the old vanes, inserting the new ones and reinstalling the head. In a matter of minutes, the pump can be back in operation. Simple vane replacement also requires no special tools.

For owners of liquid terminals, the result is optimized operating efficiency: less power consumption, less repair and maintenance, less wasted or contaminated product, more speed and precision in loading and unloading, and more consistency in blending.

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