Is it ideal to have almost zero movement in sustained condition while selecting a variable spring or otherwise certain movement ( in sustained condition ) should be ignored if it is serving the desired purpose.

That depends on the individual piping system. Typically a variable spring hanger is designed to balance the system in the Operating (hot) condition. Therefore depending on the relative stiffness of the hanger to the associated piping, you can see some displacement at the hanger location in the Sustained case.

(Rememeber, a variable spring hanger balances the system in only one position / condition. All other positions / cases are not balanced and you can expect some displacement at that location.)

Thanks alot Richard.

Regards,
Sarvesh Kumar