Pressure drop measurement based on Flow measurement


I have to measure the pressure drop of a 300ml, closed system @2lpm using a flow meter and a differential pressure gauge, the problem is that without the system the measurement setup has already so many losses that when I add the system it goes above the maximum pressure that I can measure.

Since the system adds 300ml to the circuit, and the airflow is created by negative pressure, could I estimate the pressure loss using the airflow change when the system is plugged and when it is not?