valve, and is packed with india-rubber con-tained in the packing ring. This latter ringis adjusted by set screws, and their loosenessis prevented by ratchets and springs, whichalso indicate—by the clicks—the movementof the screw. Messrs. Napier’s and Rennie’spractice is shown by Figs. 135 and 136, inpages 284 and 285. Both firms, it will benoticed, prefer the set screws outside thecasing, and the face ring is recessed in thecover. Messrs. Napier adopt spiral springsaround each screw, and two packing ringswith the packing between them. Exceptingthe springs, Messrs. Rennie’s mode is preciselysimilar. In page 285, Fig. 137 is alluded toas Messrs. Maudslay’s valve. They use anovel packing ring, shown at a large scale, insection, by Fig. 140. This is a face ring of
Pig. 140.
SPRING
MESSRS. maudslay’s packing ring ior slide valve.
Peculiar section packed with india-rubberPacking, and the ring enclosing the same isapported on curved springs of steel. Thisarrangement is self-adjusting, and the firm
have adopted it for some time without failurein any case. It will be seen, from theseexamples, that the back of the valve isunexposed to the steam; and to furtherrelieve the face surface, a communicationwith the condenser and the annular spacewithin the packing ring is sometimes intro-duced. By enlarging the face ring thesteam can be arranged to lift the valve, ifdesired, from the facing, and thus reverse thesituation of the friction. Another example ofself-adjusting packing of a more simple form,than Messrs. Maudslay’s is shown by Fig. 138,in page 286. Besides the Messrs. Dudgeon,Messrs. Penn have often used it, being simplya ring of metal packed with india-rubber underit.
SLIDE VALVE LINK MOTION.
It is, of course, well understood that theutility of the portion of the marine engine nowto be noticed is a combination of detail toproduce three effects at will—starting, stop-ping, and reversing. Now, were it only re-quisite to produce the means for starting andstopping, the mechanical appliances would bea simple matter; but when reversing must beaccomplished by the same gear, the simplicityand effectiveness of the arrangements demandcloser attention. In common with the otherclaims on marine engineers, they have notbeen behind in producing what was requisitein the present case ; each maker escaping eachother in design, but yet all accomplishingsimilar results.
The first example now brought into noticeis that by Messrs. Penn, lately fitted by themin H.M.S.S. “Northumberland,” represented
j