146

MODERN STEAM PRACTICE.

foot of the denser steam in lbs., and multiply the square root of thequotient by 96. The product is the required velocity in feet persecond.

To find the pressure to which saturated steam is reduced when itflows freely, with a given velocity, from one vessel into another .—Multiply the square of the velocity in feet per second by the weightin lbs. of a cubic foot of steam of the initial total pressure, and dividethe product by 9216. The quotient thus found expresses the differ-ence of the initial and final pressures; subtract this quotient fromthe given initial pressure, and the remainder is the reduced totalpressure sought.

Of the loss of pressure generally which accompanies the movementsof steam. —It has been seen that a reduction of pressure, great orsmall, necessarily accompanies even the free motion of steam, thedifference being consumed in communicating that motion. By farthe heaviest losses are, however, due to the resistances of bends andsurface friction of pipes, &c. It has been found from experiment onstationary engines and boilers that the losses on various accountsfollow these general ratios.

The difference of pressures in the boiler and cylinder is—

ist. As the density of the steam, and as the square of the speedof piston.

2d. As the square of the ratio of area of piston to cross section ofsteam pipe.

3d. As a factor dependent on bends and friction.

The permanent difference of pressure caused by passing througha stricture in a pipe, otherwise of uniform diameter before andbehind the stricture, is as the density of the steam, and as thesquare of the difference of speeds through the larger and smallerparts of the pipe.

The friction of a fluid through a pipe appears to vary more orless—

ist. As the length directly.

2d. As the diameter inversely.

ßd. As the square of the velocity directly.

4th. As the density directly.