Weale. Treatise on the Steam Engine.
An account of the accident in the boiler at Greenwich
(This accident took place in 1803 on the east bank of the Peninsula – somewhere on the riverbank near the Pilot Inn).
The introduction of -the new high pressure engines was checked, in consqence of a dreadful explosion which took place on the 8th September, 1803 in one of the first of these engines which was used near London. It had been set up in a- temporary manner to drain the foundations for a large building, which was thenerecting for a tide corn-mill on the banks of the river Thames, between Greenwich and Woolwich. The temporary engine was managed by a boy, who is said to have confined the safety-valve, by placing a prop of wood upon it and jambing it under a beam in the roof. He left the engine working in this state, and went away;: another workman afterwards stopped the engine, and the-steam having no escape, burst open the boiler very soon afterwards, with an explosion as violent as the blowing up of a gunpowder mill. The noise was heard at a great distance from the place; three people were killed on the spot, and three others dangerously wounded. The boiler was made of cast iron about four feet diameter, and nearly an inch thick; it was considered to have been capable of sustaining a pressure of 500 pounds per square inch. The safety-valve was of very insufficient dimensions, and was so constructed that it could be easily over loaded by design.
This accident excited much apprehension, and showed that the high pressure engines required great precaution in constructing their boilers, to proportion them in the strongest manner, and to prove their strength before using them, as is done with cannon; also to adapt the engines properly to their work, in order that they might be enabled to perform the required task, without forcing the steam to a dangerous elasticity. Mr. Trevithick, after being thus informed of the danger of explosions, took precautions to prevent such accidents in his other engines, by applying two separate safety-valves to each boiler, to give a double security, in case of one valve sticking fast, if ever it should become rusted into its seat, or if it should be overloaded -by ignorance or design; and to prevent any evil consequences from such mismanagement, it was proposed to inclose one of the’ two safety-valves within a box, which might be kept locked, and inaccessible the engine-keeper.
The strength of the boiler was proved previously to setting the engine to work for the first time, by forcibly injecting cold water into the boiler, with a small forcing pump, until it escaped through the safety valve, which had a heavy extra load .applied upon it for the time, in order to subject the boiler to a more severe internal pressure than the steam could ever occasion when in use. An ingenious expedient was also devised to avert the danger of the boiler being injured by the fire, in case the engine-man, by neglecting to feed the boiler with water, should allow .the part exposed to the fire to become dry withinside ; a small hole was bored through that part of the metal of the boiler, which would receive the most direct action of the fire, and the hole was filled up by riveting a plug of lead fast into it: this lead would effectually withstand the heat, so long as it continued to be covered with water; but immediately after the water had wasted below the level of the hole,: the lead would melt, and by letting out the steam into the furnace, would avoid danger of explosion, and the negligence of the engineman would be made known.
By these precautions Mr. Trevithick regained so much confidence, as to obtain some orders for high pressure engines in London; but not so many as he would have received, if the explosion at Woolwich had not deterred many persons from adopting his engines.
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