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.