Chap. XXI. STEAM CONSIDERED AS A MOVING POWER.
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and each adjoining passage, increasing the diameter in the proportion of 10 to 8, therubbing surfaces remaining nearly the same, and the cone will be more eqxially pressed intothe socket. The most simple method in practice is to make use of two double-passaged cocks.
Plug Tree is a rod attached to the engine beam, and provided with tappets or projectingpieces which strike levers or handles of valves for the purpose of shutting or opening themat various intervals, as the rod descends or ascends. The handles turning on their axis actas levers, and thus move the cocks, slides, or valves, to which they are attached.
Vulves opened by Weights . — Pig. 2013. W is the weight, which acts upon an arm a on theaxis, and requires to be turned, that the valve may be moved : a spring-catch 6, held bythe suspended weight, closes the valve, which opens when the catch is disengaged, andthe handle c is moved by the tappet d: direct action from the beam itself is now used toopen these valves, and the weights are in great measure dispensed with, though they aresaid to open the valves more rapidly, which is important for working the engine, as theopening and closing the passages at the proper time constitute its effect.
A weight opening a valve may descend into a vessel of water, while the aperture bywhich the water escapes from under it may be increased or diminished at pleasure. Theweight uses its full force to open the valve, but when it be-gins to move, it is stopped by the water: in the ascent, avalve at the bottom of the vessel opens inwardly, and theengine has only to raise the weight again. This method isin constant use for opening valves of engines for the purposeof raising water. 1
Eccentric Rollers , to raise the valve-rods, are ingenious,though attended with some objections in their application.
Fig. 2012. shows a section of the steam pipes and valves ofFenton and Murray’s double engine, and fig. 2011. the com-municating rods : by the pipe C the steam enters : at a is athrottle-valve, which regulates its supply: a governor of two
Fig. 2011
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Fig. 2012. pbnton’s steam-pipb and valve.
bent levers e, e, turning upon its axis at^ has a rotary motion communicated to it by meansof a band passing from a pulley to a similar pulley at d. The upper part of the spindle has aslide n, which is connected by rods *,i, to the levers, which rises when the centrifugal forceof the governor is increased, and descends when it decreases; as the lever l is affectedby the rising or falling of the balls of the governor, so is the valve a attached to it.