438

MODERN STEAM PRACTXCE.

attained. Still further to diminish the noise, the lift of the india-rubber discs is limited bymeans of a curved guard, hav-ing a boss at the centre; thisboss rests on the seating, andis bored out for receiving oneend of the holding-down bolt,the other end passing througha cross piece of wrought iron,which bears on the under sideof the round hole over whichthe grating for the disc of indiarubber is placed. The holein the india-rubber disc shouldfit loosely round the bossformed on the guard, and inno case should the india rubberbe pressed down on the seat-ing. These gratings consistof annular rings and ribs ra-diating to the centre of theboss, thus forming a number ofoblong holes through whichthe water passes. The guardalso requires to be pierced withholes, as the discs of indiarubber have a tendency towork or close slowly, werenot the water acting on thetop surface and pressing itdownwards on the returnstroke. Some of these valveseatings are secured by brassstud bolts and nuts, withlugs cast on the seating forbolting them down over theholes left in the condenser

casting, the joint being made Fig . 32T. —Arrangement of Valves adopted for Air

with a ring of india rubber Pump -

a, Gräting. b, India-rubber valve. C C, Guards.recessed into the SCelting'J D r>, Studs for guards.

Fig. 320.—Single Valve for Air Pump .a, Valve seat. b, India-rubber valve. c, Guard.d, Holding-down bolt. e, Cross bar.

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