Hi I am having trouble to measure the volume flow of a rebound valve with a venturi flow meter. The valve itself starts to open at a certain pressure. But it doesn’t open completely at this point. In the beginning it is more like a flapping which in turn causes fluctuations. With rising pressure it begins to settles to more steady values. [0.5 inch ]---- > pressure regulator ----[ 0,5 inch ]---> flow meter –---[0.5 inch ]--> valve The inlet of the valve is about 0.8 mm in diameter. My venturi nozzle is 0.5 inches in diameter. I added 100 cm before and 30 cm behind the nozzle to get a laminar flow. I alter the pressure with a pressure regulator by hand and plot a pressure / flow diagram. The date gets recorded automatically. My Problem is that I am not able to record any reasonable measuring date! It gets all messed up by the fluctuations. Is there any way how I can reduce the fluctuations? I tried a few alternations in the setup of my measurement section. The only thing that really did improve my measurement was when I added a narrow pipe, 6 mm, between the venturi flow meter and my valve. But that functioned more like a lowpass and reduced the flow speed to much. The flow speeds are between 0 – 800 l/min. Pressure regulator and flow meter are able to handle this flow speed. How can I improve my measurement? Thanks in Advance.