This paper describes the design and development of three low-cost ventilators which can be mass produced to meet a surge in demand for such equipment. Each of these ventilators is having unique features while meeting standard functional specifications of mechanical ventilators. The first design works on compressed air source as control gas and does not require electrical power for its operation. Parameters like tidal volume, breathing rate etc. can be set mechanically in this ventilator. Second one is an automated Ambu bag based system, which has digital controller providing closed-loop control of critical ventilator parameters and a very unique geared actuation system that ensure long cyclic life to Ambu bag and fine control of parameters. The third design is an air blower based pneumatic circuit ventilator which is a state of the art ICU ventilator. Mathematical modeling of the systems is carried out to design the mechanical/electrical control elements and to simulate the performance of the system. Prototypes of ventilators were developed, testing and simulation runs were carried out and critical parameters were measured ensuring satisfactory performance of the system.