434

MODERN STEAM PRACTICE.

all the valves, as before described. The gratings for these valvesare formed of ribs radiating from the centre, having one or moreconcentric rings, keeping the area of each hole in the grating equalto about i square inch. The ribs on the guard radiate from thecentral boss, and the ends of the elongated apertures are roundedor left square as taste may dictate. Other forms of valves areoblong shaped, folding up against a flat guard, the india rubberbeing secured at the middle with stud bolts; the holes in thegratings being made hexagonal, formed around a circle I inch indiameter. This grating resembles a honeycomb, and may be saidto combine the greatest area with the least material, thus obtainingmore free way for the passage of the water—a very desirable pointto attain in designing pump valves. For this object a valve seathas been designed by the author in which five discs can be placedin about the same space as is usually occupied by one; the seatingis in the form of a square box open at the bottom, with a flangeall round for securing it to the condenser, one valve being placedon the top and one on each of the four sides. This plan can bemodified by making the valve seating cylindrical, the side valvebeing simply a band of india rubber, secured at one end to thecylindrical seating, and a round disc valve placed on the top. Theaction of the band valve is one of expansion and contraction as itopens and shuts with the reciprocating motion of the pump piston,or plunger if so fitted. It is scarcely necessary to state that india-rubber valves will work in any position, whether lying flat, or at anangle, or even inverted; the latter position is fast finding favour,where the passages of the pump are so arranged that the watergravitates into the pump chamber instead of being sucked ordrawn in.

The pistons for the circulating pumps of direct-acting horizontalengines are packed with a metallic ring; in some instances woodpacking has been adopted, lignum-vite being preferred. In othercases plungers instead of pistons are used. The plunger consistsof a cylinder of brass working in a central stufifing box, hemppacking being used in the form of a gasket. The cylinder formsas it were the pump barrel and piston, as in the double-actionpump: it is worked directly off the steam piston, with a small rodsecured to the cylinder with a single nut. It may be argued thatthe plunger is heavier than a plain piston, but it must be remem-bered that as it is surrounded with water, it partially floats as it were