VALVE. A device or appliance for control ling the flow of liquids, gas, or loose material through a pipe, chute, or other form of passage way. With the general use of steam, water, gas, and other fluids. a great variety of valves have been invented and are in daily use. These valves bear various trade names based on their purpose, the shape or motion of the valve, and the method of operation. Thus we have safety valves, globe valves, slide valves. screw valves, etc. Valves generally, whatever their specific names may be, can be included in a general classification with reference to the manner in which their motion is obtained, or in a general classification with re gard to the motion relative to the valve seat. In the first classification are: (1) Valves opened and closed by band; (2) valves operated by in dependent mechanism; (3) valves operated by mechanism connected with the machine whose operation they control; and (4) valves opened and closed by the motion of the fluid whose flow they control. Classified with regard to their motion relative to the valve seat there are: (1) valves which rotate in the opening, (2) valves which rise and fall perpendicularly from and to their seats, and (3) valves which open and close by sliding on and parallel to their seats. It obvious that the characteristics of the first and second classifications may be combined in one ral•e; thus a slide valve may be operated by hand like the ordinary hand screw gate valve, by separate mechanism like the hydraulic gate valves for water-works, or by mechanism con nected with the medium operated like the slide valve of a locomotive. The construction of some common forms of valves is as follows: A gap valve consists of a disk hinged at one side so as to open and close like the lid of a coffee pot. A
butterfly valve consists of a disk hinged at diametrically opposite edges and slit through the centre at right angles to the hinges so that the two flaps swing upward and away from each other when the valve opens. Another construction con sists in placing the hinges together on the dia metrical slit so that the two flap upward and toward each other. A disk valve consists of a circular disk seated on a grid and free to slide up and clown for a limited distance on a rod or bolt passing through a bole in its centre. Lift or poppet mitres consist of a disk with a flat or beveled edge seated on a circular disk; they operate by their own weight, like a disk valve, or by means of springs or rods. Slide Valves are of various forms. The D ealre and the piston valve, illustrated in the article on Loco MOTIVES, are examples. The gate valve used on water mains consists of a metal disk sliding be tween two seats inclined toward each other so as to form a wedge-shaped slot. This disk is also wedge-shaped to correspond with the slot, and is raised and lowered by a stem attached to its upper edge and screwed up and down by a hand wheel. Cocks consist of a conical plug seated in a conical casing: both plug and easing have a bole through them in the line of the pipe, and by turning the plug so that the holes coin cide the valve is opened. Valves are usually made of metal, cast iron, bronze, brass, and steel, combined with rubber, leather, or other flexible material to secure tightness. See Am COMPRESSOR ; GAS; LOCOMOTIVE; PUMPS AND PUMPING MACHINERY; STEAM ENGINE; WATER WORKS.