MARINE ENGINES.

391

rod is screwed (Fig. 272), having a raised screwed part at both endsand double nuts; by this means the valve can be very accuratelyset at any time. The hole through the valve should be slightly

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oblong, to allow for the wear and close contact between the faces ofthe valve and cylinder. The valve rod, in some examples, is guidedat the end through a hollow brass pipe, or a stuffing box and gland,similar to the front end. In other arrangements the end of thevalve spindle is screwed into a nut recessed in the valve casing; thethrust is taken on the end of the nut, and the pull on projections