OSCILLATING- ENGINES.
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Other examples have no casings, butsimply a valve, seating, weight, and handle;while a fourth is an ordinary stop valve andlever.
Each valve of course has to perform, bydifferent modes, the same action or effect. Nowwith the example shown by Fig. 66—page236—mechanical action is certain when thevalve is released, and with that by Fig. 67,below, self action is caused; but should thevalve hang or leak, the vacuum will be im-paired, although space above the valve isallowed for the accumulation of water toTender the valve air tight.
SELF-ACTING 8NIFTING VALVE.
CYLINDER RELIEF VALVES.
When water accumulates in the cylinder acertain space is occupied by the fluid, andwhen the piston is at the full stroke, a compression of the volume must ensue. Now,
apart from considering whether the waterenters the cylinder either from the priming ofthe boilers or any other cause, immediateattention is now directed to the best means ofmeeting the evil alluded to. As the pistondrives the water in front of its travel, it isobvious that the position of the valves inquestion must be at the extremities of the
Fig. 68.
CYLINDER SPRING RELIEF VALVE.
cylinder. The above illustration, Fig. 68,is an ordinary example of a relief valve,spring, and seating, often fitted, and providedfor, on cylinders of oscillating engines.The nut on the upper extremity of the spindlerelieves the valve from the effect of the springif requisite. The positions of the illustrateddetails as at the bottom end of the cylinder,and a reverse position will be that for the topend. The spring is of course always actingon the valve, and the latter rises only whenthe pressure in the cylinder overcomes that ofthe spring. The valve is the disc kind, guidedbelow the seating by a spindle, and above bya bracket secured to the cylinder by threestuds and nuts. The bracket also receives the