Reciprocating Pumps vs. Multi-Stage Centrifugal Pumps

Many times, you may be faced with the decision to use a reciprocating pump or a multi-stage centrifugal pump for a given application. There are some pros and cons for either pump design, depending on:

• Where the pump is to be installed
• The fluid being transferred
• Future expansion plans
• Variable system parameters
• Operation and maintenance issues
• Personnel knowledge and experience with the pumps
•  

1. Operating Principles

Centrifugal Pump
A centrifugal pump adds kinetic energy to a fluid by means of fast-rotating impellers. There is no fixed volume, and the fluid increases in kinetic energy (velocity) while moving through impeller passages by centrifugal force resulting from impeller rotation.
Its accelerated velocity is converted into pressure head by exiting into the diffuser for discharge, or - in the case of a multi-stage centrifugal pump - it further increases its velocity (pressure head) by moving through to the next fast-rotating impeller (see Figure 1). Centrifugal pumps are usually direct coupled with drivers (electric motors or engines) without speed reduction.

Figure 1. A schematic of a typical centrifugal pump.

Reciprocating Pump
A reciprocating pump utilizes a crankshaft-connecting rod mechanism identical to internal combustion engines.  The crankshaft-connecting rod mechanism converts the rotary movement of the crankshaft to a reciprocating linear movement of plungers or pistons. The plunger/piston movement creates volume changes.
As a cavity opens when a plunger/piston retracts, the fluid is admitted through an inlet check valve. When the plunger/piston reverses, the inlet check valve closes, and the cavity reduces when the plunger/piston extends. The outlet check valve opens and the fluid is forced out by the plunger/piston.
The discharge volume is fixed for each crankshaft revolution, regardless of the fluid being pumped. Pressure is determined by the system flow resistance and pump construction (see Figure 2). Speed reduction is needed for decreasing high speed from the driver to low pump shaft speed.

Figure 2. A typical reciprocating plunger pump.