Vacuum Applications Beryllium Copper Bellows Nomenclature Bellows Movements Standard Tolerances Multiply or Laminated Bellows Neck Trims Explanation of Tabulated Data Ordering Instructions Multiply or Laminated Bellows Any standard-size bellows can be fabricated with multiply construction up to four plies of equal thickness. The maximum pressure, spring rate, and stability pressure are increased in direct proportion to the number of plies, but with the same axial deflection as a single ply. Multiply design permits a lower spring rate and a greater cycle life than a single ply configuration for an equivalent pressure. This type of construction is recommended for applications with vibration or rapid cyclic motion because of the inherent damping provided by the relative movement of the plies. Multiply construction in not recommended for vacuum application requiring a mass spectrometer helium leak test because of possible out-gassing from an undetectable leak in an inner ply. Refer to the individual topics in the Explanation of Tabulated Data for the methods used to calculate multiply bellows parameters.