▁primary ▁ring ▁whereas ▁non - push er ▁secondary ▁se als ▁are ▁static ▁and ▁associated ▁with ▁bell ows ▁se al ▁rings . ▁ ▁Spr ings ▁ ▁In ▁order ▁to ▁keep ▁the ▁primary ▁se aling ▁surfaces ▁in ▁int imate ▁contact , ▁an ▁actu ating ▁force ▁is ▁required . ▁ ▁This ▁actu ating ▁force ▁is ▁provided ▁by ▁a ▁spring . ▁In ▁conj unction ▁with ▁the ▁spring , ▁ax ial ▁forces ▁may ▁also ▁be ▁provided ▁by ▁the ▁pressure ▁of ▁the ▁se aled ▁fluid ▁acting ▁on ▁the ▁se al ▁ring . ▁ ▁Many ▁different ▁types ▁of ▁spr ings ▁are ▁used ▁in ▁mechanical ▁se als : ▁ ▁single ▁spring , ▁multiple ▁spr ings , ▁wave ▁spr ings , ▁and ▁metal ▁bell ows . ▁ ▁Hard ware ▁ ▁The ▁term ▁" hard ware " ▁is ▁used ▁to ▁describe ▁various ▁devices ▁which ▁hold ▁the ▁other ▁components ▁together ▁in ▁the ▁desired ▁relationship . ▁ ▁For ▁example , ▁a ▁retain er ▁might ▁be ▁used ▁to ▁package ▁the ▁se al ▁ring , ▁secondary ▁se aling ▁element ▁and ▁spr ings ▁into ▁a ▁single ▁unit . ▁ ▁Another ▁example ▁of ▁hardware ▁is ▁the ▁drive ▁mechanism ▁which ▁is ▁necessary ▁to ▁prevent ▁ax ial ▁and ▁rot ational ▁sli pp age ▁of ▁the ▁se al ▁on ▁the ▁sh aft . ▁ ▁Class ifications ▁ ▁There ▁are ▁a ▁number ▁of ▁different ▁ways ▁in ▁which ▁“ se als ” ▁may ▁be ▁class ified . ▁ ▁Sometimes ▁a ▁reference ▁to ▁a ▁“ se al ” ▁may ▁be ▁to ▁a ▁se aling ▁system ▁whereas ▁other ▁times ▁the ▁reference ▁is ▁to ▁a ▁device ▁such