The Power of a Hydraulic Power Unit

Lumberjacks. Miners. Search and rescue crews. What do they have in common? They also all work some with extreme machinery in their daily jobs. But where does a someone find enough power to lift a massive tree, move huge volumes of earth, or drag a car out of a canyon? The answer is that the machinery they use are almost universally driven with a hydraulic power unit— a motor that converts the motion of liquid into mechanical force.

A hydraulic motor, at its essence, is fairly simple: a reservoir of hydraulic fluid, a power unit, and a machine that can be moved by any form of rotation. The power unit — usually a small electric device — pressurizes the fluid. Because fluid cannot be compressed, any amount of pressure from the pump causes the fluid to move, usually through a series of valves designed to make sure that the fluid can’t move backwards and harm the pump.

At the far end of the line, the fluid moves into a piston, which extends as it fills up, and voila! — a log is lifted easily off of the earth, swung about, and dropped onto a waiting truck. Or, perhaps, the fluid moves through a propeller, which generates a rotational force that is then fed into a series of gears that slows the rotations-per-minute but adds a huge amount of torque, and the winch on the far side of those gears pulls a truck out of a lake. The number of potential applications is huge.  After the fluid has done its job, it returns back to the reservoir along a different line, ready to be used again the next time the pump comes online.

Electric motors can only generate more power by being built bigger — so to get an electric motor to haul a ton of earth directly, you need one that is absolutely massive. But by using a hydraulic power unit — which is, ultimately, an electric motor, just used in conjunction with a hydrostatic system — the same job can be accomplished with a much smaller device.