▁a ▁trade ▁secret . ▁Another ▁important ▁in vention , ▁one ▁which ▁W att ▁was ▁most ▁proud ▁of , ▁was ▁the ▁parallel ▁motion ▁which ▁was ▁essential ▁in ▁double - act ing ▁engines ▁as ▁it ▁produced ▁the ▁straight ▁line ▁motion ▁required ▁for ▁the ▁cyl inder ▁rod ▁and ▁p ump , ▁from ▁the ▁connected ▁rock ing ▁beam , ▁whose ▁end ▁moves ▁in ▁a ▁circular ▁arc . ▁This ▁was ▁pat ented ▁in ▁ 1 7 8 4 . ▁A ▁thro tt le ▁val ve ▁to ▁control ▁the ▁power ▁of ▁the ▁engine , ▁and ▁a ▁cent rif ug al ▁governor , ▁pat ented ▁in ▁ 1 7 8 8 , ▁to ▁keep ▁it ▁from ▁" running ▁away " ▁were ▁very ▁important . ▁These ▁improvements ▁taken ▁together ▁produced ▁an ▁engine ▁which ▁was ▁up ▁to ▁five ▁times ▁as ▁efficient ▁in ▁its ▁use ▁of ▁fuel ▁as ▁the ▁New com en ▁engine . ▁ ▁Because ▁of ▁the ▁danger ▁of ▁expl oding ▁bo ilers , ▁which ▁were ▁in ▁a ▁very ▁primitive ▁stage ▁of ▁development , ▁and ▁the ▁on going ▁issues ▁with ▁le aks , ▁W att ▁restricted ▁his ▁use ▁of ▁high ▁pressure ▁steam   – ▁all ▁of ▁his ▁engines ▁used ▁steam ▁at ▁near ▁atmos pher ic ▁pressure . ▁ ▁Pat ent ▁tri als ▁ ▁Edward ▁Bull ▁started ▁construct ing ▁engines ▁for ▁B oul ton ▁and ▁W att ▁in ▁Corn wall ▁in ▁ 1 7 8 1 . ▁By ▁ 1 7 9 2 ▁he ▁had ▁started ▁making ▁engines ▁of ▁his ▁own ▁design , ▁but ▁which ▁contained ▁a ▁separate ▁cond enser , ▁and ▁so