Mechanical ventilator, a machine designed to move breathable air into and out of the lungs, to provide breathing for a patient who is physically unable to breathe, or breathing insufficiently. Various Ventilator modes are discussed with diagrams. Main parts of ventilator such as piston, compressor, Oxygen Sensor, CO2 sensor, MR 850 Respiratory Humidifier are discussed elaborately with Maintenance, Repair and Trouble shooting guides. Non invasive Facial masks are shown with figures. Endotracheal tube circuit is explained. Ventilator circuits with tube, Heated humidifier with level detector, Resistance wire, temperature sensor to control are illustrated. Expiratory flow sensor used on intensive care ventilators to measure a patient's exhaled gas flow from the expiratory limb. Different types of Flow Sensors such as Hot-wire anemometer, Orifice Plate, LVDT are discussed with figures. Various Test Lungs are available to test the ventilator circuit prior to put to the ventilator to clinical use (patient). PEEP (Positive End Expiratory Pressure) setting is possible to keep some air in alveoli. Alarm Situations of Low Pressure , High Pressure, Low PEEP/CPAP, Apnea, Low Gas source pressure or Power are available with ventilators. High-frequency ventilation is a type of mechanical ventilation which utilizes a respiratory rate greater than four times the normal value. {(>150 (Vf) breaths per minute)} and very small tidal volumes is explained with figures.