A single sealed unit containing the cylinder, pump, motor, reservoir and control. It takes electrical power and a command signal and produces hydraulic force, with no separate power unit, no hoses and no hydraulic system elsewhere for anyone to maintain.

Hydraulic force density with electric installation simplicity. No reservoir to check, no filters to change, no hoses to burst, and no risk of contaminating a machine or product with oil. It installs like an electric actuator and behaves like a hydraulic one.

It delivers considerably more force for its size and is much stiffer under load, which matters where the actuator must hold position against a varying force. Electric actuators are simpler still and better suited to lighter duty, so the choice turns on how much force is genuinely needed.

Substantially, on any duty cycle with stationary periods. A conventional system runs its pump continuously whether or not the actuator moves; a self-contained unit runs only when commanded and holds position with the motor stopped, so it consumes and generates a fraction of the energy and heat.

Force and stroke are bounded by what fits in a self-contained package, and duty cycle is limited because the small internal oil volume has little thermal capacity to absorb heat. Continuous high-frequency cycling is where these actuators run out of capability first.

Generally not in the field - the sealed construction that removes the maintenance also means failures are handled by replacing the unit. That is worth factoring into the whole-life cost, particularly on applications where a spare unit would need to be held. Whole-life cost should include that, not just the purchase price.

Applications needing a few high-force actuators rather than many - dam and sluice gates, machine positioning, test equipment, tilting and clamping. Where a machine has many actuators, a central power unit serving all of them remains more economical, so the count of actuators is usually what decides between the two approaches.