335 
Steam Engine. 
wards, by the side of the piston. To prevent any devia- 
tion of the quantity of oil by the working of the engine, 
means must be provided to restore it to the requisite 
height, as cocks, valves, Stc. regulated by a float or floats 
upon the surface of the oil, or by means of a pump or 
pumps worked by the engine itself, or otherwise. By 
the interposition of the oil, between the piston and the 
condenser, ail waste of steam, by passing the piston, is 
effectually prevented, and a consequent saving of fuel is 
effectedc 
JFoolf^s method of measuring the elastic force oj Stearm 
PLATE I, of this number exhibits a measured section 
of the self-acting and regulating steam valve. A A re- 
presents the upper part of the boiler, having its mouth or 
neck cylindrical, and closed by a well-fitted, but easily 
moving valve plug, B B C C, which is in fact a metallic 
tube, open at bottom and closed above, by a cap-piece B 
B, that by its chamfered rim or projecting part affords the 
accurate valve-closure when down. The interior parallel 
lines at D shew the place where a long perforation is made 
through the side of the cylindrical part of the valve plug 
from its cap, nearly down to the bottom ; which perfora- 
tion affords a passage for the steam, increasing in magni- 
tude as the elastic force causes the valve to rise. E is the 
side passage for conveying the steam to its place of ope- 
ration. F is the rod cr tail of the valve passing through 
a stuffing box above, and attached by a chain to the sec- 
tor G, and by its means moving the lever that carries the 
ball IL 
The above constitutes the whole of this simple and effec- 
tual contrivance, and its mode of operation scarcely needs 
to be described. As the steam becomes stronger it raises 
the valve, and escapes through D, and raises the weight 
H higher the more the pressure within exeeeds that of the 
working steam in the upper space F E. 
