Separate Condenser
A Scottish instrument maker, James Watt, was given the job in 1763 of repairing a model Newcomen engine for the University of Glasgow, and noted how inefficient it was.
In 1765 Watt conceived the idea of a separate condensation chamber. Watt's idea was to equip the engine with a second, small cylinder, connected to the main one. In Watt's design, the cold water was injected only into the condensation chamber. This type of condenser is known as a jet condenser. Because the chambers were connected, this caused condensation without significant loss of heat. The condenser remained cold and under less atmospheric pressure than the cylinder, while the cylinder remained hot. When the piston, propelled by steam, reached the top of the cylinder, the steam inlet valve closed and the valve controlling the passage to the condenser opened. External atmospheric pressure pushed the piston towards the condenser.
A further improvement to the system of condensation was to dispense with the jet of cold water, and cool the condenser by immersing it in a cold water tank. This type of condenser is known as a surface condenser.
At each stroke the warm condensate was drawn off and sent up to a hot well by a vacuum pump which also helped to evacuate the steam from under the power cylinder. The still-warm condensate was recycled as feedwater for the boiler.
Watt's next improvement to the Newcomen design was to increase the power of the engine by sealing the top of the cylinder and injecting low-pressure steam into the upper part of the cylinder, instead of relying on atmospheric pressure. The power of the low-pressure steam would assist the vacuum created by the condensation, increasing the power of the down stroke, and the speed of the engine.
These improvements led to the fully developed version of 1775 that actually went into production.
Read more about this topic: Watt Steam Engine
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