REGULATION OF STEAM.

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for the valve is suited for the under side of the top port and the upperside of the bottom port, while the exhaust takes place at the top andbottom edges of the steam-ports. The face on the cylinder is gene-rally made of brass, rivetted to the cylinder, with brass pins screwedinto the cast-iron. The valve-gear for paddle-wheel engines isgenerally fitted with a loose eccentric, revolving with the mainshaft, having all the necessary stops on the eccentric and the shaftfor the forward and backward movements, the eccentric rod endtaking a lever on the weigh-shaft, fitted with the usual gab forthrowing the valve out of gear, having a long lever handle on theweigh-shaft for working the valve by hand. As these valves are attimes very stiff to rnove, provision is made for securing a rope to theend of the lever, so that a number of men may be employed to shiftb them. The weigh-shaft is fitted with a lever for the valve rod, andanother for the back balance weight. This dass of valve was gene-rally used for the side-lever engine, and it is evidently desirablethat it should be capable of being easily and quickly handled, asmen pulling at a rope, perhaps when the vessel is pitching androlling about in a heavy sea, is inconvenient and dangerous. Awheel and pinion, therefore, is sometimes introduced to securegreater ease in working the valve.

The slide-valve for oscillating engines is generally of the sametype as is adopted for land engines, being fitted with a pack-ing ring on the back of the valve to relieve it from much of thesteam pressure. The valve mechanism being entirely different fromany other dass of engine, the eccentric is loose on the shaft, andfitted with all the necessary stops for the forward and backwardmovements, The eccentric rod is fitted with a gab at its end,working on a pin attached to an open curved link, made so as tosuit the oscillation of the cylinder; a rod passing upwards is forgedalong with the link, having means of guiding it at the top with abracket fitted to the head-stock or framing for the main-shaft, thelink itself being guided at the bottom with suitable slides, fitted tothe pillars for supporting the head-stock. This valve gear, in itssimplest arrangement, has a plain handle, fitted with a rod forattachment to the quadrant, with a means of throwing the gab on theeccentric rod out of gear; thus the valve can be moved very quicklyfor small engines. The cylinder is usually fitted with two valves,but sometimes with only one; the double arrangement is introducedto balance the cylinder.. The valve spindles have guide-bars forged