166

MODERN STEAM PRACTICE.

piston; and in this way the outgoing stroke or descent of the pumprods may be very slow indeed. The plug rod, ascending, shuts offtlie equilibrium valve, thus stopping the further descent, or produc-ing only a slight motion, of the plunger and weight, until thecataract releases the exhaust and then the steam valve. It willthus be seen that for a part of the downward stroke the steam andexhaust valves are both open, and the exhaust remains so until theend of the stroke, when it is closed; while in the up stroke of thepiston the equilibrium valve is open, and all the rest shut off.

In order still further to explain this intricate valve gear, in Figs.102, 103, we give an example fitted to an engine at one of ourCornwall mines, the diameter of the steam cylinder being 90 inches.“ The action of the gear will be better understood if we describeeach stroke separately. First, the steam, or indoor stroke:—This isthe down stroke of the piston, and is produced by the admission ofsteam through a valve termed the steam valve, situated in the topnozzle, and which is actuated by means of the lever B fixed on anarbor carried in bearings in the two upright Castings at the sides,which are termed arbor posts. It is usual to connect the lever Bdirectly with the steam-valve lever—by means of a rod carried up-ward, instead of indirectly by means of a rod carried downwards, asin the example before us; the reason for the latter arrangement wewill explain as we go on. The lever B is attached by means of arod with a ‘treadle’ or weighted lever of wood situated under theengine-house floor; the treadle is connected to the steam-valvelever, so that when the lever B is raised it closes the steam valve.On the steam arbor, or the arbor carrying the lever B, is placeda quadrant K, which is supported by means of the catch U, whichcatch keeps the steam valve closed tili the cataract rod A shallhave released the quadrant K by means of the lever M, and thusallowed the weighted treadle to pull down the lever B and open thesteam valve. The cataract is actually the governor of the engine,and acts in the following way. (See illustrations of cataracts, Figs.104, 105, 106.) In this case a plunger is attached to the lever, onthe opposite side of the fulcrum is placed the cataract rod A, andon the plunger side of the fulcrum a weight. The plunger worksin a kind of force pump, fixed in a cistern full of water. When theplunger is raised water follows it up through the suction valve, andduring the down stroke the water thus drawn from the cistern isforced back again through a delivery valve which is capable of being