i6o

MODERN STEAM PRACTICE.

The valve is a disc of leather, with top and bottom plates of wroughtiron, securely rivetted through and through, and it is held inPosition by a central bar of iron, with long projections on the

under side for taking the entirediameter of the valve. A key isdriven through the bar, drawing itup against the under side of theseating, which likewise pressesdown the bar placed on the top ofthe leather; thus the valve hinges,as it were, on the mid feather, andis perfectly water-tight. The valveis prevented from opening too farby pieces forged on the bar, and atthe top of the bar a bow is formed,for attaching a hook and chainwhen drawing the clack fromthe surface, as provision must bemade that the clack can be drawnwhen the water is above the valve-chest door. Some of these valveshinge on a bar, which passesthrough lugs forged on the top^ r plate and through holes in the

bow, for fishing the valve to whichthe bow is securely bolted; thereis also a wrought-iron piece at thecentre of the valve seating on whichthe valve hinges. There should bea slight play in the holes to suitthe varying thickness of the leatherforming the valve.

The working bücket (Fig. 97) is constructed similarly to theordinary clack valve with leather hinge, having means of attachingthe bar to the pump rods; and is packed with deep rings of gutta-percha, let into recesses formed on the outside circumference, andpressed against the barrel with hydraulic pressure, holes being boredfrom the top of the bücket for this purpose. This plan is muchmore preferable than the old mode of packing the bücket with aplaited gasket or ring of leather.

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Fig. 96.-—Clack Valve with Wrought-ironHinge Plates.

a, Clack seat. b, Leather disc. c c, Hingeplates. d, Round bar for hinge. E, Bow.f, Centre stud.