Clearance (in a sealing system)

The space between components in a mechanical system which is present to allow for manufacturing, thermal, and dynamic variations in the size and position of the components. As measured, it is equal to the distance between the sealing surface and the entrance to the seal groove. In a radial sealing system, this will be the space between the O.D. of the shaft or piston and the I.D. of the bore. As the clearance in a system increases, the tendency of the seal to dislodge from the groove and enter into the clearance space also increases, especially in applications where pressure is present. Anti-extrusion measures should be considered in these cases. Care should be taken in radial applications to note whether clearances are being stated as radial clearances or as diametrical clearances.