Axial Piston PumpEdit
An axial piston pump has a number of pistons (usually an odd number) arranged in a circular array within a housing which is commonly referred to as a cylinder block, rotor or barrel. This cylinder block is driven to rotate about its axis of symmetry by an integral shaft that is, more or less, aligned with the pumping pistons (usually parallel but not necessarily).
Internal lubrication of the pump is achieved by use of the operating fluid -- normally called hydraulic fluid. Most hydraulic systems have a maximum operating temperature, limited by the fluid, of about 120 ºC (250 ºF) so that using that fluid as a lubricant brings its own problems. In this type of pump the leakage from the face between the cylinder housing and the body block is used to cool and lubricate the exterior of the rotating parts. The leakage is then carried off to the reservoir or to the inlet side of the pump again. Hydraulic fluid that has been used is always cooled and passed through micrometre-sized filters before recirculating through the pump.
This type of pump can contain most of the necessary circuit controls integrally (the swash-plate angle control) to regulate flow and pressure, be very reliable and allow the rest of the hydraulic system to be very simple and inexpensive.
Radial Piston PumpEdit
These kinds of piston pumps are characterized by the following advantages:
- high efficiency
- high pressure (up to 1,000 bar)
- low flow and pressure ripple (due to the small dead volume in the workspace of the pumping piston)
- low noise level
- very high load at lowest speed due to the hydrostatically balanced parts possible
- no axial internal forces at the drive shaft bearing
- high reliability
A disadvantage are the bigger radial dimensions in comparison to the axial piston pump, but it could be compensated with the shorter construction in axial direction.
Due to the hydrostatically balanced parts it is possible to use the pump with various hydraulic fluids like mineral oil, biodegradable oil, HFA (oil in water), HFC (water-glycol), HFD (synthetic ester) or cutting emulsion. That implies the following main applications for a radial piston pump:
- machine tools (e.g., displace of cutting emulsion, supply for hydraulic equipment like cylinders)
- high pressure units (HPU) (e.g., for overload protection of presses)
- test rigs
- automotive sector (e.g., automatic transmission, hydraulic suspension control in upper-class cars)
- plastic- and powder injection moulding
- wind energy