then flow out of the seal and on to the rear face plate, which cools the system and prevents any excess heat from building up. This fluid cycle is continuously repeated while the seal is in operation. Applications Hydrostatic seals were first developed in the early 1960s to control the sealing of compressor air in the aircraft industry. Recently hydrostatic seals have only been used in the compressor industry because hydrodynamic seals have much greater application. The hydrostatic seal also has great potential in the chemical industry since it can be used to transport and seal chemicals. However, the chemical industry has set very strict regulations and the seal cannot be used for certain chemicals because of the constant seal leakage. Generations of hydrostatic seals First generation The first hydrostatic seal was developed to replace current hydrodynamic seals; previous hydrodynamic seals were costly to manufacture and were tedious to assemble. First generation hydrostatic seals used a two pressure system to establish equilibrium at the seal face. The seal face was developed to work under high pressure conditions, however the seal face began to warp and deteriorate during stress tests. Once ammonia ( the liquid used in the first hydrostatic seal ) was added, the two seal faces would make contact with each other and begin the erosion process. Cold water was then tested as the incompressible fluid, it has double the viscosity as ammonia, which showed favorable results. Since cold water had double the viscosity of ammonia, the water prevented the seals from making contact with each other, thus causing the system to run properly. First Generation: Issues - High pressure conditions - recycles fluid in a continuous cycle, may have stagnant fluids which cause blockage - Seal faces began to erode under certain circumstances Second Generation The second hydrostatic seal was an attempt to resolve first generation hydrostatic seal problems: erosion of seals, high pressure build up, and stagnant fluids. Second generation hydrostatic seals had a redesigned seal face; new face control grooves were added to help stabilize the seals while under extreme conditions. Prior to the face control grooves, the seal faces were not balanced and would begin to move under high pressure conditions. Due to the movement, the seal faces would become misaligned when the seals moved, and that caused the seal faces to deteriorate, resulting in an unusable seal. Second generation: Upgrades - attempt to fix