REGULATION OF STEAM.

*25

of the port; and again 9S-r-38 = 2'5 inches, this is the linearopening of the port by the valve for a single port. As double-ported valves are generally adopted, the linear opening of each willbe i‘25 inches.

The steam ports in the cylinder are much in excess of this, thearea for the steam port being T \- of the cylinder area, and for thecentral exhaust yi of the cylinder area is generally allowed,—

=171 square inches for the steam port,

— 396 square inches for the exhaust port.

Thus we would have for steam port 171-1-38 = 4/5 for main steamport on cylinder, but as two are required the width of each will be2*25 linear inches. As double-ported arrangements have a bridge orstrengthening piece on the centre line of the steam port, say 1 inchbroad, we would have four steam ports in the cylinder, 19 incheslong and 2}^ inches wide. The exhaust or central port in the cylinderis 39^4 inches long, and say 10 inches wide, or nearly so, to givethe required area, care being taken that the passages into con-denser are not contracted.

SETTING OUT THE VALVE FACES.

5 2

5 2

u. *

inches.

We will suppose the lap of the valve is. lfä

The width of the outer steam ports on cylinder. 2%

The width of the outer exhaust port equals the half travel of valve.... 33^

The width of face on valve. 13^

The width of the inner steam port. 1 %

The lap of valve for inner steam port. 1%

The width of inside steam port on cylinder. 2%.

The width of face on cylinder. 1 3 ^

The half width of exhaust port. 5

20%

20 ^ X 2= 41 % inches, is the length of the slide valve.

The face on the cylinder between the outer and inner steam portsis found as follows:—

VALVE Ss

Fig. 68.

wMm,.

CYLINDER