▁is ▁to ▁reduce ▁the ▁magnitude ▁of ▁mechanical ▁contact . ▁In ▁general , ▁face ▁treat ments ▁provide ▁a ▁means ▁of ▁modifying ▁the ▁pressure ▁distribution ▁between ▁the ▁se al ▁faces ▁through ▁hydro static ▁or ▁hyd rod ynamic ▁top ography . ▁ ▁Se al ▁face ▁top ography ▁refers ▁to ▁the ▁three ▁dimensional ▁aspects ▁of ▁the ▁se al ▁face ▁surface . ▁ ▁Bal ance ▁ratio ▁▁▁ ▁In ▁addition ▁to ▁the ▁spring ▁force , ▁the ▁se al ▁faces ▁are ▁pushed ▁together ▁through ▁pressure ▁acting ▁hydro stat ically ▁on ▁the ▁geometry ▁of ▁the ▁se al . ▁ ▁The ▁ratio ▁of ▁the ▁geometric ▁area ▁t ending ▁to ▁close ▁the ▁se al ▁faces ▁to ▁the ▁area ▁t ending ▁to ▁open ▁the ▁se al ▁faces ▁is ▁called ▁the ▁balance ▁ratio . ▁ ▁P ush er ▁or ▁bell ows ▁se al ▁ring ▁▁ ▁P ush er ▁se als ▁employ ▁a ▁dynamic ▁secondary ▁se aling ▁element ▁( typ ically ▁an ▁O - ring ) ▁which ▁moves ▁ax ial ly ▁with ▁the ▁se al ▁ring . ▁ ▁Bell ows ▁se als ▁employ ▁a ▁static ▁secondary ▁se al ▁( such ▁as ▁an ▁O - ring , ▁high ▁temperature ▁graph ite ▁pack ing , ▁or ▁el ast omer ic ▁bell ows ▁and ▁ax ial ▁movement ▁is ▁accommod ated ▁by ▁contra ction ▁or ▁expansion ▁of ▁the ▁bell ows . ▁ ▁Spring ▁design ▁ ▁Many ▁different ▁types ▁of ▁spr ings ▁are ▁used , ▁including : ▁ ▁relatively ▁large ▁single ▁co il ▁spr ings , ▁multiple ▁sets ▁of ▁small ▁co il ▁spr ings , ▁and ▁wave ▁spr ings . ▁