The clearance gap seal is a simple sealing form by using a small gap between the moving parts. The sealing effect depends on the gap size and pressure difference, the seal length and the surface quality of the part. Among them, the gap size and its uniformity have the greatest impact on the sealing performance.
Therefore, this seal has high requirements on the geometry and surface machining accuracy of the part. Since there is a gap between the mating parts, the friction is small, the heat is small, and the service life is long. Since no sealing material is used, the structure is simple and compact, and the size is small. The gap oil seal is generally used for dynamic sealing (dynamic sealing, refers to sealing coupling and There is relative motion), such as the seal between the plunger and the plunger hole of the hydraulic pump and the hydraulic motor; the seal between the valve body and the spool.
The disadvantage of the gap seal is that the gap cannot be completely prevented due to the presence of the gap, so it cannot be used where the leakage is prohibited. In addition, when the size is large, it is difficult to achieve the surface machining accuracy required for the gap seal, so for large diameters such as large hydraulic cylinders, gap seals are generally not used. Gap seals are only suitable for smaller diameter control devices such as control valves.
