210 



OF THE PARTS OF 



[SECT. vn. 



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. l 



The engines of the following steam vessels are fitted with Seaward's patent 

 slide-valves, viz. 



The Volcano 

 Megsera 

 Naslednik 

 Vivid 



Water Witch 

 Emerald 

 Duchess of Kent 

 Ruby 

 Gem 

 Topaz 



City of Kingston 

 Paris 



horse power 



150 

 150 

 190 

 190 

 140 

 130 

 100 

 80 

 70 

 100 

 190 



f Government Packets. 

 Russian Packet. 



" | Hull Packets. 

 ? Ramsgate and Boulogne Packets. 



Gravesend Packets. 



Jamaica Packet. 



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. 



