With centrifugal pumps – the fluid enters the pump near the axis and the rotor accelerates the fluid circumferentially and compresses it against the rim, generating high pressures (hundreds of bar is not uncommon), and if the outlet backpressure is not too high, high flow rates.
Complexities of centrifugal pumps
Centrifugal pumps have a reputation for being extremely hard to design to get optimum performance, it is not uncommon for pumps to only deliver low tens of percent efficiency; whereas a well engineered and debugged pump can manage 70-90%. In some applications low efficiency may not be a problem, but in rocketry it is critical. Turbopumps in rockets are important and problematic enough that launch vehicles using one have been caustically described as a ‘turbopump with a rocket attached’- up to 50% of the total costs have been ascribed to this area.
The areas of common problems include:
- Excessive flow from the high pressure rim back to the low pressure inlet along the gap between the casing of the pump and the rotor.
Excessive recirculation of the fluid at inlet.
- Excessive vortexing of the fluid as it leaves the casing of the pump.
- In addition the precise shape of the rotor itself is very critical.