1L and 2L oxygen generators belong to health care type. When the gas flow rate is adjusted to 1L/MIN, the oxygen concentration can reach 90%. But for the patient, the airflow is very small.
3-liter and 5-liter oxygen generators belong to medical type. Patients must use 3 liters or 5 liters.
When the gas flow rate of the 3-liter machine is adjusted to 3 liters/minute, the oxygen concentration can reach above 95%.
For patients, air circulation is enough. A 5-liter machine is usually used by two people at the same time or with a ventilator.