Hydraulic cylinders on mobile equipment have used, for the most part, solid rods. It is well known, however, that a circular cross-section does not result in optimal utilization of the material from a flexural rigidity standpoint, and long cylinders (e.g., on hydraulic cranes) have been designed by utilizing hollow rods. In some designs, these rods are subjected internally to the same pressure as the cylinder (‘wet’ rods), while in other designs they are non-pressurized (‘dry’ rods). The question naturally arises as to the superiority of one design over the other.
This paper presents comparative data on pressurized and non-pressurized hollow rod cylinders and solid rod cylinders, based on the analysis of the cylinder-rod combination as a stepped beam-column structural member having a non-linear rotational joint at the cylinder rod interface. It is concluded that, generally speaking, hollow rod construction results in better utilization of materials than solid rods, but pressurization does not result in any significant increase in structural capability.