210
OF THE PARTS OF
[sect. VII.
of the steam from the cylinder two similar slide-valves move on faces
attached to the eduction pipe, and may also be moved conjointly or separately:
but it is not always necessary that there should be two distinct slides and faces
within the induction pipe; in small double action engines the two steam
passages may be brought so close, that one steam slide working over both apertures
will answer the purpose. By this arrangement, each slide is pressed against the
face on which it moves, by the simple pressure of the steam, and thus any water
that may accumulate within the cylinder is driven back to the steam pipe, the
valves being lifted off their faces by its pressure. The eduction and steam-slides
being entirely distinct from each other, although set in motion by one eccentric,
and one set of hand-gear, may be adjusted to expand the steam through any
portion of the stroke, which is important when high pressure steam is employed.
Amongst other advantages of these valves may be mentioned, simplicity of action
and management, no trouble of packing and adjustment, and yet perfectly tight
with the least possible friction; also they are so constructed that each slide-valve
and face may be easily detached without affecting any one of the other principal
valves and faces. 1
The engines of the following steam vessels are fitted with Seaward’s patent
slide-valves, viz.
Volcano
Megaera
150 horse
150 -
power ]
j* Government Packets.
Naslednik
150 -
-
Russian Packet.
Vivid
Water Witch
190 -
190 -
- -1
j> Hull Packets.
Emerald
Duchess of Kent
140 -
130 -
-1
Ramsgate and Boulogne Packets.
Ruby-
Gem
100 -
80 -
: ;1
> Gravesend Packets.
Topaz
City of Kingston
70 -
100 -
: : J
f
Jamaica Packet.
Paris
190 -
-
Havre and Hamburgh Packet.
Rotary Valves.
452. Axis valves are the most simple of the valves moved by rotary motion.
A valve of this kind consists of a plate of metal fixed on an axis in the passage;
the axis crosses the centre of the plate, and is made to pass through an air-tight
aperture to the outside : they are extremely useful where perfect tightness is not
required, as in the throttle valve, for dampers and the like. Belidor applied an
axis valve to pump work, by putting the axis a little to one side of the centre;
1 For further description, see the Appendix.