The early vacuum steam engine had limited efficiency, but it was safer because its pressure was relatively low. When the material was damaged, the machine shrank inward instead of exploding outward.
Their efficiency is limited by external air pressure, cylinder deformation, combustion and boiling efficiency and condensation capacity. The theoretical maximum efficiency is limited by the relatively low boiling temperature of water at ordinary atmospheric pressure. The use of high temperature and high pressure steam greatly improves the efficiency of steam engines. But this kind of steam engine is much more dangerous than vacuum steam engine.
The explosion of boilers and machines caused many serious accidents. The safety valve has brought great improvement here. When the pressure is too high, the safety valve deflates and depressurizes. But the real guarantee of safety only depends on the experience and safety rules of construction, operation and maintenance.
Savery made the world's first practical steam pump, and obtained the British patent named "Friends of Miners" at 1698.
He first filled an egg-shaped container with steam, then closed the steam inlet valve and sprayed cold water outside the container to condense the steam in the container to form a vacuum. Open the water inlet valve, and the water at the bottom of the mine is sucked into the container through the water inlet pipe under the action of atmospheric pressure; Close the water inlet valve, reopen the steam inlet valve, and use steam pressure to press the water in the container out through the drain valve.
When the water in the container is drained and filled with steam, close the steam inlet valve and drain valve, and spray water again to condense the steam. In this way, the two egg-shaped containers work alternately and can continuously drain water.
Extended data:
Watt improved the steam engine;
In the early days, Watt's steam engine still used the balance bar and pull rod mechanism to drive the water pump. In order to remove the condensate and air from the condenser, Watt installed an air pump. He also installed an interlayer on the outer wall of the cylinder and heated the cylinder wall with steam to reduce condensation loss.
Watt's creative work made the steam engine develop rapidly. He turned the machine that can only carry water into a widely used steam engine, which doubled the thermal efficiency and greatly reduced the coal consumption. Therefore, Watt is a reformer of steam engine.
References:
Baidu encyclopedia-steam engine