In this article we present a clinically validated invasive emergency mechanical ventilator developed in Chile called VEMERS UC. It has been clinically tested and validated in intubated Covid19 patients. Once the pandemic hit Chilean soil in March 2020, it was clear that the number of mechanical ventilators available would not be enough. As in other parts of the world many initiatives sprung, most of them naively simple. Chilean medical societies joined engineering specialists and agreed early on in an organized and regulated open process for validating emergency mechanical ventilators, thus allowing for rapid development but with the required functionality, reliability, and safety features. VEMERS UC was one of few that completed successfully all stages of the validating process, the final test being on five critically-ill intubated COVID-19 patients for eight hours each. VEMERS UC is based on an electro-pneumatic circuit architecture and its components are all low cost, off-the-shelf pneumatic and electronic products easily obtained in industrial markets. It works in continuous mandatory volume control mode. The novel technical features of VEMERS UC are discussed here as well as the results obtained in each stage of the validating process. The validating process carried out in Chile is noteworthy by itself, and it could be used as an example in other developing countries. Furthermore, VEMERS UC can be used as a guiding design reference in other countries as well, since this design has already been thoroughly tested in human patients and has proven to work successfully.