HEATING BY HOT WATER. 2138 
down these valves are both water and steam tight. The 
Fig. 154, 
“sluice” valves (Fig. 155) 
consist of a sliding disc, or 
sluice, actuated by a spindle, 
screw, and wheel, as before, 
butwhen screwed down fitting 
tightly against a planed 
face fitted in the casting 
(see Fig. 156). When 
properly made these are even superior to the serew- 
Fig. 155. 
Fig. 156. 
down or dise valves, the area of the opening being fully 
equal to that of the interior of the 
piping, and the passage also direct, with- 
out any diversion or obstruction of the 
current whatever. One of these forms 
must be employed wherever an abso- 
lutely tight stoppage has to be made, 
as in disconnecting one boiler from 
another one, or from the pipes, for 
the purpose of repairs, or wherever 
the water has to be kept back as well 
as the current checked. 
Fila. 167. 
