In volume cycled ventilator the inspiratory flow rate is set at:
Normal initial settings for a ventilator are - tidal volume: 500 ml, frequency: 10-12 breaths/min, inspiratory flow rate: 60-70 liters/min, I:E ratio = 1 :2, delivered oxygen concentration (FIO2) 50%.
Inspiratory flow is the velocity with which the breathing gas is supplied to the patient.
If inspiratory flow is less than patient flow demands the patient will try to increase his inspiratory effort and this will increase the work of breathing which is not desirable. If inspiratory flow is high there will be increased airway pressure which can cause barotrauma and increase dead space which is again not desirable.
So a flow of 60-70 liters/minute is adequate (in COPD patients a higher flow rate of 80-100 liters/min is required to increase the expiratory time).