retainer. If a preloaded system is used the force between the cylinder shaft and piston head is initially the piston head retainer preload value. Once pressure has applied this force will reduce. The piston head and cylinder shaft shoulder will remain in contact unless the applied pressure multiplied by the piston head area exceeds the preload. The maximum force the piston head retainer will see is the larger of the preload and the applied pressure multiplied by the full piston head area. The load on the piston head retainer is greater than the external load, which is due to the reduced shaft size passing through the piston head. Increasing this portion of shaft reduces the load on the retainer. Side loading Side loading is unequal pressure that is not centered on the cylinder rod. This off-center strain can lead to bending of the rod in extreme cases, but more commonly causes leaking due to warping the circular seals into an oval shape. It can also damage and enlarge the bore hole around the rod and the inner cylinder wall around the piston head, if the rod is pressed hard enough sideways to fully compress and deform the seals to make metal-on-metal scraping contact. The strain of side loading can be directly reduced with the use of internal stop tubes which reduce the maximum extension length, leaving some distance between the piston and bore seal, and increasing leverage to resist warping of the seals. Double pistons also spread out the forces of side loading while also reducing stroke length. Alternately, external sliding guides and hinges can support the load and reduce side loading forces applied directly on the cylinder. Cylinder mounting methods Mounting methods also play an important role in cylinder performance. Generally, fixed mounts on the centerline of the cylinder are best for straight-line force transfer and avoiding wear. Common types of mounting include: Flange mounts—Very strong and rigid, but have little tolerance for misalignment. Experts recommend cap end mounts for thrust loads and rod end mounts where major loading puts the piston rod in tension. Three types are head rectangular flange, head square flange or rectangular head. Flange mounts function optimally when the mounting face attaches to a machine support member. Side-mounted cylinders—Easy to install and service, but the mounts produce a turning moment as the cylinder applies force to a load, increasing wear and tear. To avoid this,