Answer
In hydraulic cylinders, spiral rings often face dynamic axial loads that fluctuate with pressure cycles. The Safety Factor $SF$ is the ratio of the calculated Thrust Capacity $P_r$ to the Maximum Operating Load $P_{max}$. $SF = \frac{P_r}{P_{max}}$. For static loads, a $SF$ of $2$ is common. For dynamic or shock loads, the $SF$ should be increased to $3$ or $4$. The calculation must also account for the 'Groove Material Factor' $K_g = \frac{\sigma_{y,actual}}{\sigma_{y,ref}}$. If the housing is made of a lower-strength material (like 6061-T6 Aluminum), the effective thrust capacity of the assembly is significantly reduced. The formula becomes $P_{eff} = P_r \cdot \frac{\sigma_{y,housing}}{\sigma_{y,ring}}$, and the $SF$ must be applied to this lower $P_{eff}$ value.
