Standard centrifugal pumps are not self-priming and require the fluid end to be primed prior to activation. This can be accomplished by installing the pump in a location that provides a flooded suction or by using a device to prime the pump. Once the pump casing is full of fluid, it can then be energized. Running a pump dry or restricting suction flow can severely damage the fluid end, mechanical seal, or packing. The designs of self-priming pumps result in turbulent flow patterns, which cause excessive wear during pumping of abrasive fluids and increase operating costs. The drilling industry avoids using self-priming pumps due to increased downtime and costs.
READING CENTRIFUGAL PUMP CURVES
A centrifugal pump curve comprises a grid depicting head and flow rate and a series of lines that illustrate pump performance characteristics. Figure 1. is a typical pump curve, and each set of lines will be reviewed individually.
SIZING CENTRIFUGAL PUMPS
Many factors affect performance of a centrifugal pump and must be considered during pump selection. This chapter describes conditions that affect the centrifugal pump and is followed by details that will assist in eliminating negative conditions that cause pump failure.
CASING OF CENTRIFUGAL PUMP
The function of the centrifugal pump casing is to:
- Direct fluid into the eye of the impeller through the suction inlet.
- Minimize fluid recirculation from impeller discharge to impeller suction.
- Capture fluid discharge from the impeller in the case volute to most efficiently utilize work performed by the impeller and direct fluid away from the impeller. (See Picture 1. and 2.)