In our video we show how it is possible to fabricate a flexible valve in-situ within a microfluidic channel. We used PEG diacrylate which we polymerised by UV irradiation through a photomask to obtain the desired shape. Then, we performed a full velocimetry study by flowing a 0.2% aqueous solution of 200 nm polystyrene particles. Taking advantage of the Ghost Particle Velocimetry technique, we obtained the speckle pattern via white light illumination and we analysed the flow field via cross correlation. Finally, we obtained the full flow field of the pulsed flow across the flexible valve.