▁of ▁Dur am et all ic ▁about ▁ 1 9 4 2 . ▁ ▁By ▁ 1 9 5 4 , ▁mechanical ▁se als ▁were ▁used ▁with ▁such ▁regular ity ▁in ▁the ▁ref ining ▁and ▁process ▁indust ries ▁that ▁the ▁American ▁Pet role um ▁Institute ▁included ▁se al ▁specific ations ▁in ▁the ▁first ▁edition ▁of ▁its ▁Standard ▁ 6 1 0 , ▁" Cent rif ug al ▁P umps ▁for ▁General ▁Re fin ery ▁Services ". ▁ ▁By ▁ 1 9 5 6 , ▁many ▁of ▁the ▁concept ual ▁designs ▁and ▁application ▁gu idel ines ▁that ▁are ▁in ▁use ▁today ▁had ▁been ▁developed . ▁ ▁Com mer cially ▁available ▁designs ▁included ▁both ▁rot ating ▁and ▁station ary ▁flexible ▁elements , ▁bal anced ▁and ▁un bal anced ▁hyd ra ul ic ▁loading , ▁rub ber ▁and ▁metal ▁bell ows , ▁and ▁a ▁wide ▁variety ▁of ▁spring ▁designs ▁and ▁types . ▁ ▁Second ary ▁se aling ▁elements ▁included ▁O - r ings , ▁wed ges , ▁U - cu ps ▁and ▁various ▁pack ings . ▁ ▁Car bon - graph ite ▁was ▁widely ▁used ▁as ▁a ▁se al ▁face ▁material ; ▁the ▁m ating ▁se al ▁face ▁was ▁often ▁cast ▁iron , ▁Ni - res ist , ▁ 4 0 0 ▁series ▁st ain less ▁steel , ▁St ellite ▁or ▁al umin um ▁ox ide ▁although ▁t ung sten ▁car b ide ▁was ▁coming ▁into ▁use . ▁ ▁St ain less ▁steel ▁was ▁widely ▁used ▁for ▁spr ings , ▁retain ers , ▁sle e ves