MARINE ENGINES.
439
while the guard is secured to the seating by a plain bolt and nutThe plan now universally adopted is to cast a number of thesecircular gratings in one large brass seating, which is bolted downover the oblong holes left in the casting; this brass plate isstrengthened with bars on the under side, and has a flange allround for the holding-down bolts, which are screwed in the castingas studs with nuts on the top; the guards are fastened down to thevalve gratings by a stud bolt passing through each guard, havinga nut bearing on the top of the guard; in other cases the stud is
formed with a collar to screw upagainst in the grating, whichcollar is somewhat deeper thanthe thickness of the india rubber,and the guard is bolted down onthe top of it. All the nuts onthese studs should have split pinspassing through the points of thebolts, to prevent the guards shak-ing loose. In some arrangementsthe valve seats are all bolteddown to one brass seating, havinga number of large holes left init and bored out for their recep-tion; and when the large plateis properly planed on the surface,and all the small gratings turned,the joints may be simply me-tallic, with a little thin red leadplaced between the surfacesbefore they are bolted down. Insome instances it is advisable toplace a number of valves in asmall space; with this object inview, as well as to decrease thecircumferential opening of the valves, and yet give a large areafor the passage of the water, the valve seating may be made inthe form of a square box, open at the bottom, with side flangesall round for bolting it to the condenser casting. With thisform one valve can be placed on the top and one on each side,making five valves in all; thus with this arrangement, and the same