Good Things Come in Small Packages

In tandem with the development of micro hydraulic pumps was the development of various components to power and control them. Besides Hydro Leduc and Bieri Swiss, there are companies that exist which specialize in miniature valves such as the Lee Company, specializing in valves for aerospace, down-hole oil tools, machine tools, medical/scientific instrumentation and ink-jet printing. Of course, micro hydraulic systems are a form of power transmission just like any other hydraulic system so they need an input power source. Companies such as Maxon motors specialize in miniature electric motors that are used to power these hydraulic systems.

As I mentioned above, downhole tools were the first application for micro hydraulics and probably one of the most demanding applications for any hydraulics system: a harsh environment with extreme vibration and temperature and a fixed space envelope for the hydraulic system, typically limited to less than 40 mm in diameter. The micro hydraulic power units consist of small, high-speed electric motors powered from the surface, driving micro hydraulic pumps. The pumps in turn typically supply linear actuators that can be used to anchor the tool in the well bore, for example, but can also power micro hydraulic motors for taking core samples. A typical micro hydraulic motor would have a fixed-displacement, axial piston design with a displacement in the range of 0.45 cm3/rev (0.027 in3/rev).

Since their inception, micro hydraulics have branched out into other demanding applications. In the environmental sciences, micro hydraulics allows oceanographic researchers to perform thermal profiling of the Earth’s oceans. Drifting buoys use micro hydraulics to ballast the buoy so it can be controlled to dive and stop at various depths, take temperature readings and then resurface to transmit data. These are high pressure, high performance applications because the buoys operate at depths up to 2000 m (6561 ft) where hydrostatic pressure is 200 bar (3000 psi) and the buoys must operate for 1.5 years with no human contact.

Another interesting application for micro hydraulic is handheld battery powered crimping/cutting tools. Similar to the common cordless drill, this unit contains a miniature 0.080 cm3/rev (0.0048 in3/rev) hydraulic pump running at 2000 rpm with a maximum pressure rating of 550 bar (7970 psi). This pump provides flow to actuators that can produce forces up to 6 metric tonnes at maximum pressure, all in a tool that is handheld and battery powered.