You will observe, therefore, that the plain
slide valve engine gives the most general satisfaction at about
two-thirds cut off and a very low economic result. The best of such
engines will require forty-five to fifty pounds of steam per horse
power per hour, and to generate this, assuming an evaporation of nine
pounds of water to a pound of coal, would require between five and six
pounds of coal per horse power per hour. And the only feature that the
valve has specially to commend it is its extreme simplicity and the
very little mechanism required to operate it.
Yet this is of considerable importance, and in consideration of some
special features at its latest cut off, the attempt has been many
times made to take advantage of these features. For instance, at 90 deg.
advance, the valve opens very rapidly indeed and fully satisfies our
requirements of a perfect valve. This is one good point, and in this
position also the exhaust and compression can be regulated very
closely and as desired without much lap, and as the opening of the
exhaust port comes with the eccentric at its most rapid movement the
release is very quick and as we would have it. This is only possible
at the most uneconomic position of the valve as regards cut off.
Pages:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25