Peripheral Pumps / Regenerative Pumps |
Note: In the sections below this type of pump is designated a regenerative pump..
The regenerative pump produces large head at comparatively small flows.
The design of the pump includes for a special impeller with a large number of radial
blades. As the fluid is discharge from one blade it is transferred to the root
of the next blade and given additional energy. The fluid heads developed in
this type of pump can be very high and the pump should not be used without a close coupled
relief valve in the system.
In a regenerative pump, liquid enters and exits the pump during several revolutions
of the impeller. The velocity and pressure increases of the liquid are
therefore gradual compared to the centrifugal pump. Liquid entering the pump near
its vapor pressure is less likely to experience the pressure change that can cause
cavitation due to the smaller pressure gradient. Therefore, regenerative pumps, typically, require lower net positive suction heads
than centrifugal pumps.
This pump is generally made from special materials to combat the corrosive conditions
resulting from the high degree of turbulence experienced within the casing.
The figure below shows in outline the operating principles of the peripheral pump.
Comparison between Regenerative and Centrifugal Pumps
1) The regenerative pump can handle liquids with 20% entrained gases. Under the same conditions a centrifugal pump
would experience vortexing or cavitation.
2) If the fluid supply source runs dry the regenerative pump cavity remains filled with
liquid, unlike centrifugal pumps. This allow the pump to operate under
dry suction conditions in this event.
3) The regenerative pump is capable of reversible impeller rotation,
with an accompanying reversal of the suction and discharge porting.
4) The head capacity curve of a regenerative turbine pump has a different
shape compared to a centrifugal pump. It is nearly linear sloping downward.
At lower heads, the flow is typically much smaller than for a centrifugal pump.
The slope never approaches a horizontal plane. Therefore, throttling a valve for
a regenerative pump will permit more precise changes in flow, without major
overshooting or undershooting of the duty point.