Hydraulic Cylinder Failure

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Standard cylinders are not designed to take a side load. Care must be taken to ensure that binding does not occur during extension or retraction. A designer will use one of the mounting methods shown in Fig. 7.15 to prevent binding. Also, it is often necessary to provide guides to ensure that the load follows the prescribed pathway. As with any design, it is important to plan for a disturbance from an atypical direction, particularly for cylinders mounted on mobile machines. It is generally less expensive to protect from a side load than to replace a damaged cylinder.

cylinder-mounting-method

Long cylinders supported at one end become a slender column as they extend under load. Manufacturers typically provide a nomograph that can be used to select the rod size for a given stroke length. Sometimes, a longer cylinder bore and rod size must be selected to provide the needed structural strength. Fig. 7.16 gives the ANSI symbol for a cylinder where the diameter of the rod compared to the bore is critical to circuit function.

cylinder-ANSI-symbol

From mechanics of materials, the maximum load that can be carried by a column is

cal-1

The body of a cylinder filled with oil does not function like a solid column or a hollow column, thus Eq. (7.1) can be used for an approximation, but it is not a replacement for the information given in the design nomograph. It is always a good idea to get specific design help from the manufacturer’s technical support staff.

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