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At present, in our men-of-war, the boilers are proportioned for natural draft, burning about twelve pounds of coal per square foot of grate per hour, and for a steam-pressure of fifteen pounds per square inch.
Every minute or two he pulled the chain and yanked the furnace door open to throw in the coal, shutting the door again after each shovelful, to keep the fire hot. The fireman on a fast locomotive is kept extremely busy, for he must keep the steam-pressure up to the required standard 150 or 200 pounds no matter how fast the sucking cylinders may draw it out.
Under ordinary circumstances a three- to five-minute interval is sufficient in the case of all steam-pressure, vacuum including mercurial columns and barometer superheat and temperature readings. Gland and Hot-Well Regulation There are two highly important features requiring more or less constant attention throughout a test, namely the gland and hot-well regulation.
When raised the steam was cut off, and all that was then under the piston was condensed by a jet of cold water. The outside air-pressure then acted upon it and pushed it down again. In this down-stroke by air-pressure the work was done. The far end of the walking-beam was even counter-weighted to help the steam-pressure.
Riveros also sent word down to his engine-room staff that the very last knot was to be got out of his ship, and the effect of the increased steam-pressure was soon observable on the Blanco. At about a quarter to eight there was another change of tactics on the part of the Peruvians.
The machinery was under the floor. There have been thousands of miracles since then performed by natural agencies, and there have passed many ages since Hero's machine during which not to understand a thing was to believe it to be supernatural. From the time of Hero until the seventeenth century there is no record of any attempt being made to utilize steam-pressure for a practical purpose.
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