Seals are used throughout the technology spectrum to prevent products form leaving their container or preventing foreign products to enter. With the sealing of rotary parts like shafts the seal needs to not only provide sealing capabilities, but also simultaneously allow for the desired movement without too much friction or wear. This is often accomplished using rubber rings in combination with lubricating oils. The focus of this thesis is on the design and physics of ferrofluid seals, which doesn't cause wear to the shaft and is inherently leak free. A major problem with ferrofluid seals is that when the medium to seal is (sea)water, the fluid tends to degrade over time and leads to failure of the seal. The liquid reacts with the particles or carrier, causing a deterioration of the ferrofluid's properties. Research shows a seal life time can be obtained of up to roughly 300 days, as opposed to rubber lip seals holding out for several years. A method described in this thesis is used to provide a longer life time of the seal. Analytical methods are used to determine the critical pressure and are compared with the setup to judge the performance of the setup.