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Static. A static hydraulic seal is located in a groove and sees no movement - only sealing within its confined space, acting like a gasket. To achieve this the gasket should be under pressure. The pressure is applied by tightening of the bolts. Examples of static seals include O-rings, flange seals, and cover seals. Dynamic
A hydrodynamic seal is a type of mechanical seal. A hydrodynamic seal uses a dynamic rotor with grooves that act as a pump and create an air film that the opposing sealing surface will ride on. A hydrodynamic seal performs better than hydrostatic seals by providing greater film stiffness, lower leakage and lower lift off speeds.
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.
Pusher seals employ a dynamic secondary sealing element (typically an O-ring) which moves axially with the seal ring. Bellows seals employ a static secondary seal (such as an O-ring, high temperature graphite packing, or elastomeric bellows and axial movement is accommodated by contraction or expansion of the bellows.
Fluid bearings generally have very low friction—far better than mechanical bearings. One source of friction in a fluid bearing is the viscosity of the fluid leading to dynamic friction that increases with speed, but static friction is typically negligible. Hydrostatic gas bearings are among the lowest friction bearings even at very high speeds.
A seal is a device or material that helps join systems, mechanisms or other materials together by preventing leakage (e.g. in a pumping system), containing pressure, or excluding contamination. The effectiveness of a seal is dependent on adhesion in the case of sealants and compression in the case of gaskets .
Dynamic stretches are done to warm up before a workout and static stretches are done to cool down. Stretching reduces injury risk, relieves sore muscles and increases flexibility.
The physical sealing performance of square rings in static applications is superior to that of O-rings, however in dynamic applications it is inferior to that of O-rings. Square rings are usually used only in dynamic applications as energizers in cap seal assemblies. Square rings can also be more difficult to install than O-rings.