In brief
A hydraulic pump converts mechanical drive energy into hydraulic energy by delivering pressurised fluid into a hydraulic circuit.
Contents
What is Hydraulic pump?
Hydraulic pumps work on the displacement principle: chambers that expand and contract draw in hydraulic fluid and force it into the system. Pressure is only created by the resistance of the consumers, such as cylinders or motors. Important types are gear pumps, vane pumps, axial piston pumps and radial piston pumps. They differ in pressure range, efficiency, noise behaviour and cost.
With fixed displacement pumps, the delivery volume per revolution is fixed; with variable displacement pumps, it can be adjusted to demand via controllers, for example pressure-controlled or power-controlled. Key parameters are displacement in cubic centimetres per revolution, maximum operating pressure, speed range, direction of rotation and shaft and flange design.
Many pump failures have their cause outside the pump: contaminated oil, air in the system, incorrect viscosity or cavitation on the suction side. Effective filtration, regular oil analyses and monitoring of case drain flow and noise help to detect pump damage early and prevent consequential damage in the rest of the system.
In practice: maintenance and procurement
For replacement, the type code, direction of rotation, shaft end, flange and controller version are decisive. Before installing a replacement pump, the cause of failure should be clarified and the hydraulic oil checked.
Synonyms and abbreviations: hydraulic power pump · positive displacement pump (generic term) · hydro pump
Frequently asked questions
How do you calculate the flow rate of a hydraulic pump?
The theoretical flow rate is displacement multiplied by speed. A pump with 28 cm³ per revolution theoretically delivers 42 litres per minute at 1,500 revolutions per minute. Because of internal leakage, the actual value is lower; with a volumetric efficiency of 0.95, it is around 40 litres per minute. As wear increases, this efficiency falls.
How can you recognise a worn hydraulic pump?
Typical signs are louder or changed running noise, slower movement of the actuators, system pressure no longer being reached, an increasing case drain flow and higher oil temperatures. Because similar symptoms can also be caused by valves, filters or cylinders, pressure, flow rate and case drain flow should be measured systematically before the pump is replaced.
What is cavitation and why does it damage the pump?
Cavitation occurs when the pressure on the suction side falls so far that vapour or air bubbles form in the oil. These collapse abruptly in the high-pressure area and erode material from surfaces. It can often be heard as a crackling noise. Causes include clogged suction filters, suction lines that are too narrow, oil that is too cold and therefore too viscous, or excessive speeds.