▁solution ▁was ▁the ▁Schmidt ▁system ; ▁ ▁Layout ▁The ▁Schmidt ▁system ▁used ▁a ▁se aled ▁ult ra - high - press ure ▁circuit ▁that ▁simply ▁transferred ▁heat ▁to ▁a ▁high - press ure ▁circuit , ▁by ▁means ▁of ▁he ating ▁co ils ▁inside ▁a ▁high - press ure ▁bo iler . ▁If ▁this ▁latter ▁was ▁fed ▁with ▁ordinary ▁water , ▁scale ▁could ▁form ▁on ▁the ▁outside ▁of ▁the ▁he ating ▁co ils , ▁but ▁it ▁could ▁not ▁cause ▁over he ating ▁because ▁the ▁ult ra - HP ▁tub es ▁were ▁quite ▁capable ▁of ▁with standing ▁their ▁internal ▁steam ▁temperature , ▁though ▁not ▁the ▁fire box ▁fl ame ▁temperature . ▁ ▁Press ures ▁The ▁se aled ▁ult ra - high - press ure ▁circuit ▁ran ▁at ▁between ▁, ▁depending ▁on ▁the ▁rate ▁of ▁firing . ▁The ▁H P ▁bo iler ▁worked ▁at ▁appro x ▁, ▁and ▁the ▁low - press ure ▁bo iler ▁at ▁. ▁The ▁U HP ▁and ▁H P ▁bo ilers ▁were ▁of ▁a ▁water ▁t ube ▁design , ▁while ▁the ▁LP ▁bo iler ▁was ▁a ▁fire ▁t ube ▁bo iler ▁typical ▁for ▁steam ▁locomot ives . ▁The ▁LP ▁cyl ind ers ▁were ▁driven ▁with ▁a ▁mixture ▁of ▁the ▁H P ▁cyl inder ▁exhaust ▁and ▁the ▁LP ▁bo iler ▁output . ▁Both ▁H P ▁and ▁LP ▁bo ilers ▁had ▁super he aters . ▁ ▁Ex amples ▁The ▁French ▁PL 2 4 1 P , ▁the ▁German ▁H 1 7 - 2 0 6 ▁and ▁the ▁British ▁L MS ▁ 6 3 9