The invention relates to a filter element for cleaning a fluid having a reinforced, pleated filter medium designed for radial flow. 
German Utility Model No.  DE 20 2004 003 326 U1 discloses a filter element for cleaning a fluid, which is formed as a hollow cylinder and comprises a pleated filter medium on a support grid, such that the fluid to be cleaned flows radially through the filter medium.  Conventionally, the fluid flows radially from the outside into such filters, and the interior represents the clean side, through which the filtered fluid is discharged in axial direction.  The end faces of the filter medium are sealed by cover disks, which axially terminate the filter medium in a liquid tight manner and stabilize and stiffen the filter element. 
As a rule, the pleated and annularly disposed filter medium is formed of a nonwoven or paper material, i.e., a material that has relatively little inherent stability, so that a support member is provided on the radial inside of the filter medium to increase stability.  In DE 20 2004 003 326 U1, a circumferentially extending, helically wound thread is glued to the outside and further stabilizes the folds of the filter medium particularly in circumferential direction.  This reinforcing thread extends on the peripheral side between the two axial end disks of the filter element. 
The relatively soft and unstable material of the filter medium has other disadvantages as well.  To mount or clean the filter element, an operator must grasp it, which involves the risk that pressure marks with radially pressed in folds or circumferential shifts of the filter folds occur at the peaks of the folds.  To prevent this, the filter element must either be grasped very carefully or grip protection means must be applied to the outer lateral surface, thereby increasing the structural complexity, however.