Thomas Newcomen made an improvement over Thomas Savery’s previous design. this engine, works with a atmospheric pressure to do the work. the engine pumped steam into a cylinder. the steam was then condensed by cold water which created a piston, creating strokes.
Watt solved the problem by creating the separate condenser. He added a chamber separate from the cylinder (which he also insulated), where steam would be cooled to create the necessary vacuum. This separation allowed the piston cylinder to remain the same temperature as the entering steam with no energy wasted heating it and the water inside. Additionally, the separate condenser could be kept at a much lower temperature and required less cooling.