Experiments using a zero net-mass flow actuator system and Particle Image Velocimetry PIV were performed on a NACA 4412 hydrofoil at Reynolds number of 22,000. The motivation of these studies is to analyze the changes caused by the actuation on the mean flow and pressure. The mean pressure field above the foil is obtained from the Reynolds Averaged Navier Stokes RANS equations using PIV measurements. The terms in the RANS equations involving velocities and their respective moments were extracted from the PIV data and the pressure gradient in each direction obtained as a balance. From these pressure gradients the pressure field was then obtained, both with and without open loop control. Fully attached, incipiently and fully separated cases were studied with and without actuation. For the actuation cases two different frequencies of actuation were tested.