A ventilator's power source enables it to perform mechanical or pneumatic operations, thereby converting the electrical or pneumatic energy into a useful system that provides a breath to a patient. The internal hardware that accomplishes this change is called the power transmission and conversion system. It consists of a drive mechanism and the output control mechanism.
 
The drive mechanism genrates the actual force needed to deliver gas to the patient under pressure. The output control consists of one or more valves that regulate gas flow to and from the patient.
The ventilator's drive mechanism converts the input power to useful work.
 
The type of drive mechanism determines the characteristic flow and pressure patterns the ventilator produces. Drive mechanisms can be either : 1) a direct application of compressed gas through a pressure reducing valve, or 2) an indirect application using an electric motor or compressor.