▁cool ing ▁by ▁the ▁ambient ▁air , ▁but ▁smaller ▁models ▁may ▁have ▁no ▁special ▁cool ing ▁facilities ▁at ▁all . ▁C ool ing ▁arrang ements ▁will ▁improve ▁efficiency , ▁but ▁will ▁cost ▁more ▁to ▁manufact ure . ▁ ▁Bo ost ers ▁to ▁be ▁used ▁with ▁o xygen ▁must ▁be ▁made ▁from ▁o xygen - compatible ▁materials , ▁and ▁use ▁o xygen - compatible ▁lub ric ants ▁to ▁avoid ▁fire . ▁ ▁Power ▁sources ▁ ▁Bo ost ers ▁may ▁be ▁driven ▁by ▁an ▁electric ▁motor , ▁hyd ra ul ics , ▁low ▁or ▁high ▁pressure ▁air ▁or ▁manually ▁by ▁a ▁lever ▁system . ▁Those ▁power ed ▁by ▁com pressed ▁air ▁are ▁usually ▁linear ▁actu ated ▁systems , ▁where ▁a ▁p neum atic ▁cyl inder ▁directly ▁drives ▁the ▁compression ▁p ist on , ▁often ▁in ▁a ▁common ▁housing , ▁separated ▁by ▁a ▁se al . ▁A ▁high ▁pressure ▁p neum atic ▁drive ▁arrangement ▁may ▁use ▁the ▁same ▁pressure ▁as ▁the ▁output ▁pressure ▁to ▁drive ▁the ▁p ist on , ▁and ▁a ▁low ▁pressure ▁drive ▁will ▁use ▁a ▁larger ▁diameter ▁p ist on ▁to ▁multiply ▁the ▁applied ▁force . ▁ ▁Man ufact ur ers ▁High ▁pressure ▁gas ▁boost ers ▁are ▁manufact ured ▁by ▁H ask el , ▁Dra eg er ▁and ▁others . ▁R ug ged ▁and ▁uns oph istic ated ▁models ▁( K N - 3 ▁and ▁K N - 4 ) ▁were ▁manufact ured ▁for ▁the ▁Soviet ▁Ar med ▁Forces ▁and ▁sur plus ▁examples ▁are ▁now ▁used ▁by ▁technical ▁divers ▁as ▁they ▁are ▁relatively