Because it produced superior results, the hydraulic press eventually displaced the steam hammer for metal forging. While working at Bramah's shop, Henry Maudslay suggested a cup leather packing. Joseph Bramah patented the hydraulic press in 1795. One drawback, compared to machines using gears and shafts, is that any transmission of power results in some losses due to resistance of fluid flow through the piping. The popularity of hydraulic machinery is due to the very large amount of power that can be transferred through small tubes and flexible hoses, the high power density and a wide array of actuators that can make use of this power, and the huge multiplication of forces that can be achieved by applying pressures over relatively large areas. A hydraulic system uses an incompressible liquid as its fluid, rather than a compressible gas.

Hydraulic systems, like pneumatic systems, are based on Pascal's law which states that any pressure applied to a fluid inside a closed system will transmit that pressure equally everywhere and in all directions. The fluid is controlled directly or automatically by control valves and distributed through hoses, tubes, or pipes. In this type of machine, hydraulic fluid is pumped to various hydraulic motors and hydraulic cylinders throughout the machine and becomes pressurized according to the resistance present. Heavy construction vehicles are a common example. Hydraulic machines use liquid fluid power to perform work. An excavator main hydraulics: Boom cylinders, swing drive, cooler fan, and trackdrive Fundamental features of using hydraulics compared to mechanics for force and torque increase/decrease in a transmission. For exercise equipment using hydraulic cylinders for resistance, see Resistance training.

Hydraulic jack fluid