Watt steam engine

The Watt steam engine (alternatively known as the Boulton and Watt steam engine) was the first type of steam engine to make use of a separate condenser. It was a vacuum or "atmospheric" engine using steam at a pressure just above atmospheric to create a partial vacuum beneath the piston. The difference between atmospheric pressure above the piston and the partial vacuum below drove the piston down the cylinder. James Watt avoided the use of high pressure steam because of safety concerns.