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Valves

valve, gate, fig, stem, wedge, operated, seats, gates, motion and screw

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VALVES (from Latin valve, folding doors), a mechanical appliance or device em ployed to control the flow of liquids, gases and loose material, such as sand and mud, through pipes, chutes or other forms of passages. They operate by the lifting and falling, sliding and swinging or rotating of lids, covers, balls or slides placed at the openings of or inserted in the pipe, tube or other form of passageway, as the case may be. They are usually made of metal, such as cast iron, steel, bronze and brass, often combined with leather, rubber or other flexible material, to ensure their tightness.

They are known and designated under a variety of trade and workshop names accord ing to the purposes for which they are used, the particular shape or the peculiar motion of the valve, and according to the method of their operation, thus introducing such terms as globe valve, slide valve, ball valve, safety, etc., which defy classification. On the other hand, all forms of valves may be conveniently grouped into several definite classes according to the motion of the valve relative to the valve seat and according to the manner in which that mo tion is produced.

Valves classified according to the motion of the valve relative to the valve seat are typi fied by (1) those which rotate in the opening; (2) those which lift and fall vertically from and to their seats; (3) those in which the flaps or lids are hinged to their seats and work with a swinging motion; and (4) those which open and close by sliding on and parallel to their seats. Valves classified according to the man ner in which their motion is produced may be defined as (1) those operated by hand; (2) those operated by independent mechanism; (3) those operated by mechanism actuated by the machines the operation of which is controlled by the valves; and (4) those operated by the motion of the liquid, gas or other fluid material, the flow of which is controlled by the valves.

It is quite• clear that the characteristics of these primary classifications may be combined in any one valve, as in the case of a slide valve which may. be operated in various ways: (1) by hand, as in the case of the ordinary screw gate valve ; (2) by independent mechanism, as in the case of the hydraulic gate valve; and (3) by mechanism connected with the operat ing medium, as in the case .of the slide valve of a locomotive.

Probably the most ancient form of valves are the leather flap valve, as shown at A, Fig. 1, and disc valve, shown at B, Fig. 1, commonly used in small pumps at the present time, and from which the present check and foot valve respectively are devised. The two most com mon types of valves in use to-day are the ((gate or and the the former so called because of the motion of the mechanism acting as a gate in opening and clos ing, and permitting when open a clear and unobstructed passageway for the fluid to pass through, the latter so called from the globular form of its casings. The gate valve is made in two types, "parallel seated" and "beveled seated," or "plug," and in sizes one-fourth to 96 inches, inclusive, and for all purposes, namely, water, steam, gas, oil, ammonia, etc., and for pressures varying from one pound to 5,000 pounds to the square inch; on these ac counts they are more widely used than globe valves.

Gate Valves are usually made with bronze seats, although babbitt is used in many instances. The parallel seated gate valve with inside screw, wheel type, is shown in Fig. 2, the internal mechanism of which consists of the stem C, two gates G and two beveled-faced wedges, J K, the wedges being entirely independent of the gates (or discs) and working between them. By the action of the stem, which works through the nut in the upper wedge, the gates descend parallel with their seats until the lower wedge strikes the stop (or boss) in the bottom of the case, the gates and upper wedge continuing their downward movement until the face of the bevel of upper wedge comes in contact with face of bevel of lower wedge. The gates being then down opposite port, or valve opening, the face of the upper wedge moves across the face of the lower wedge, bringing pressure to bear on the backs of both gates, from central bearings, thus forcing them apart and squarely against their seats. In opening valve the first turn of the stem releases the upper wedge from con tact with the lower wedge, thereby instantly releasing both gates (or discs) from their seats before they commence to rise. This style of valve is called the double-gate valve and when entirely opened gives a clear and unobstructed passageway. Fig. 3 represents the same type of be inspected and oiled, and the rising stem forms the best kind of an indicator. Fig. 4 is a bevel-seated gate valve, with inside screw of the double-faced solid wedge gate or plug type, in one piece, made wedge-shaped or taper ing, braced or ribbed, and by the action of the stem working through the nut in the top closes vertically between two inclined seats or sur faces in the body. To ensure perfect alignment valve with outside screw and yoke; in this case the upper end of the stem (or spindle) is threaded and the stem is operated by a nut held vertically in the yoke and turned by the hand-wheel, which is fastened to it. The stem rises without revolving, and the gates and wedges, being fastened to the lower end of the stem, rise with it. The operating screw is en tirely outside of the valve body, where it can with the stem the plug is guided by ribs or splines in the body, which engage with Frooves in the edges of the plug, and prevent it from turning and coming into contact with its seats while opening or closing. These ribs are of unequal width, to prevent the plug from being inserted wrongly after removal for repairs or otherwise. This style of valve when entirely open gives a clear and unobstructed waterway. Fig. 4 represents the same type of valve as Fig. 5, with outside screw and yoke and hand wheel, and is operated the same as Fig. 3. Fig. 6 is a parallel-seated gate valve, operated with slide stem and lever, permitting a quick opening and closing. Fig. 7 is a gate valve with motor attached, operated by electricity. Fig. 8 is a gate valve with hydraulic or pneu matic lift; in fhe former case the motive power being water to operate the cylinder, in the latter air.

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