3H
MODERN STEAM PRACTICE.
This is when the valve is between the stud or pin and the weighton lever. When great exactness is required, subtract the weight
of valve and the effective Ieverage or weight of lever from the total(steam lbs.) pressure on the valve. Examples:—
Supposing the pressure of the steam in the boiler is 30 lbs. persquare inch above the pressure of the atmosphere, giving a total of288'6i lbs. on the valve—and the length from A to B is 35 inches,and from A to C 3^ inches—we have,
ab = 35
2 = we ight on B = say 28'86 lbs.,
288'6 x 3'5
B from A = say 35 inches,
B = 28'86
= total pressure on the valve = 288'6 lbs.,
which gives the total load on the valve; to be more accurate, theweight of the valve and the effective Ieverage must be subtractedfrom 288'6, the total (steam lbs.) pressure on the valve.
WATER-PRESSURE ENGINES.
In 1846 the first hydraulic crane was erected at Newcastle-on- Tyne , for discharging ships, the supply of water being obtainedfrom the mains connected with the town Service reservoirs. After-wards one was erected at Liverpool, and another at the new dockat Grimsby . The Liverpool crane, like the Newcastle one, wassupplied with water from the town mains; but at Grimsby a towerwas built with a tank into which the water was pumped by a steamengine. In the former cases the irregularity of pressure consequent