During this covid-19, I was thinking about designing a low cost simple ventilator using a blower. There is a limit of the inspiratory and expiratory pressures, the inspiratory pressure being higher. Can anyone tell me how can I adjust the pressures? I also don't know how to control the fraction of the inhaled oxygen (FiO2). Will an oxygen concentrator work in this case? If anyone wishes to look into the plan, it is in this link.
I am going to answer the question on lowering the pressure, but I will not encourage you to use it on any patient due to the fact that professional medical equipment requires rigorous tests, using a homemade medical device would pose a large hazard on the patient.
Since your goal is to build a low cost ventilator, I believe a simple adjustable valve can lower the pressure effectively by draining part of the supplied gas away.