How to measure the outlet flow rate of a pneumatic diaphragm pump?

Our device uses a vortex flowmeter

Buffer tanks are installed on both the inlet and outlet pipes of the pump. The buffer tank must be pre-charged with nitrogen to a certain pressure; in principle, this pre-charging pressure should not be lower than 30% of the maximum operating pressure nor higher than 80% of the minimum operating pressure. Although a higher pre-charge pressure can provide better cushioning, a decrease in pressure leads to pulsations that frequently impact the bottom of the tank, causing damage to the metal components inside. When the operating pressure range is large, it is sufficient to pre-charge the pressure to 30%–35% of the maximum operating pressure. The pre-charge pressures specified by diaphragm pump manufacturers are as follows: the pre-charge pressure for the inlet buffer tank should be 80%–90% of the inlet pressure, while the pre-charge pressure for the outlet buffer tank should be 60%–65% of the outlet pressure. During actual operation, excessive vibration in the inlet pipe of the diaphragm pump indicated that the pre-charge pressure of the inlet buffer tank was not appropriate. Based on the actual conditions, the pre-charge pressure of the inlet buffer tank was reduced to 60%–65% of the inlet pressure, and the vibration was immediately eliminated, allowing the pump to return to normal operation.