A hydrostatic transmission works through the use of a pump connected to a mover that drives a hydraulic motor. The motor, powered through the generation of flow, is connected to the load. This can be used to transmit power from the primary mover to the load itself. However, many types of hydrostatic transmissions also use variable distance pumps or motors. This allows for the regulation of torque and power.
Hydrostatic transmissions take rotary power from a primary source, usually an internal combustion engine, and transmit that to a load with its own set of unique characteristics, according to Hydraulics & Pneumatics. This often necessitates the regulation of torque, power and speed. Hydrostatic transmissions can do this with a hydraulic motor. When different types of pumps and motors are added, more variables can be controlled in the power transmission process. Standard hydrostatic transmissions function only as gearboxes unless they are outfitted with these variable pumps and motors. Accordingly, the majority of hydrostatic transmissions use those pumps and motors to achieve greater utility.
Hydrostatic transmissions are often used in vehicles that have small engines and require variable speed outputs. For example, small riding mowers and some tractors have engines that utilize hydrostatic transmissions.