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Lesson 30 choosing the right valve


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Lesson 30 choosing the right valve

  1. 1. 5/29/2014 Lesson 30: Choosing the Right Valve 1/22 Choosing the Right Valve What's So Important About Choosing the Right Valve? Valves have long been more than just a simple device for turning on and shutting off flow. Valve design has kept in step with industrial progress - the development of piping techniques, and the ever-growing list of fluids for processing, power, and finished product. Progress in valve design puts at the piping engineer's elbow a great variety of valve types, each with some special qualification for service. From these he may choose the right one to provide dependable and economical performance in each particular need. It's a case of carefully matching up the valve's service characteristics with the service requirements. It's a matter of knowing every detail of the job to be done - working pressure, temperature, fluid, volume of flow, corrosive elements, valve operating cycle, etc. Other equally vital considerations are the original valve cost, installation cost, and, of course, the cost of maintenance. Crane Co., as the world's leading valve manufacturer and supplier, helps customers with the problems of valve selection every day. With this vast background of experience, Crane presents here as a helpful refresher for specifiers and buyers, the more important elements involved in choosing the right valve for the right job. Principal Valve Types Gate Valve Commonly used in industrial piping, this type of valve, as a rule, should be used as a stop turn on and shut off the flow, as opposed to regulating flow. It gets its name from the gate-like disc which operates at a right angle to the path of flow. Globe and Angle Valves The flow through globe valves follow a changing course, thereby causing increased resistance to flow and considerable
  2. 2. 5/29/2014 Lesson 30: Choosing the Right Valve 2/22 pressure drop. Because of the seating arrangements, globe valves are the most suitable for throttling flow. The valve is named after its globular body. Angle valves, similar in principle and a companion line to the globe, are designed to permit a 90 degree turn in piping and are less resistant to flow. Check Valve Sometimes referred to as the non-return valve, the check valve stops backflow in the piping. Unlike the gate and globe valves, this simplest of types operates automatically. Ball Valve Unique in design, this valve controls the flow of a wide variety of fluids. It can be opened or closed in a quarter- turn of the operating handle. The name "ball" is derived from the ball-shaped disc located within the body. A hole through the center of this disc provides the straight-through flow which is characteristic of ball valves. Light and durable, these are the valves that are playing increasingly important roles in our nation's missile projects, as well as in industry and commercial buildings. Butterfly Valve Here's a valve that is extremely durable, efficient and reliable. The butterfly valve derives its name from the wing-like action of the disc which operates at right angles to the flow. Its chief advantage is a seating surface which is not critical. The reason for this being the disc impinges against a resilient liner to provide bubble tightness with low operating torque.
  3. 3. 5/29/2014 Lesson 30: Choosing the Right Valve 3/22 Basic Gate Valve Design it should be used Gate valves are by far the most widely used in industrial piping. That's because most valves are needed as stop valves - to fully shut off or fully turn on flow - the only job for which gate valves are recommended. Gate valves are inherently suited for wide-open service. Flow moves in a straight line, and practically without resistance when disc is fully raised. Seating is perpendicular or at right angle to the line of flow - meets it head on. That's one reason why gate valves are impractical for throttling service and for too frequent operation. For instance, a 6-inch gate valve holding fluid at 300 psi, puts a load of over 4 tons on one side of the disc, if there is only atmospheric pressure on the other. While seated tight, there's no wear or undue strain on disc or seats. But each time the valve is "cracked open," there's a threat of wire drawing and erosion of seating surfaces by the high-velocity flow. Repeated movement of disc near point of closure under high-velocity flow, may create a drag on seating surfaces and cause galling or scoring on downstream side. A slightly opened disc may cause turbulent flow with vibration and chattering of disc. A gate valve usually requires more turns - more work - to open it fully. Also, unlike many globe valves, the volume of flow through the valve is not in direct relation to number of turns of handwheel. Since most gate valves used have wedge disc with matching tapered seats, refacing or repairing of the seating surfaces is not a simple operation. CONCLUSION: Gate valves, while not designed for throttling or too frequent operation are generally ideal for services requiring full flow or no flow. Gate valves are not designed for throttling In a slightly opened position high-velocity flow will cause wire drawing and erosion of seating surfaces in gate valves.
  4. 4. 5/29/2014 Lesson 30: Choosing the Right Valve 4/22 Repeated movement of disc near point of closure under high-pressure flow may gall or score seating surfaces on downstream side. Slightly opened disc in turbulent flow may cause troublesome vibration and chattering. Basic Globe and Angle Valve Design ...highly essential to piping Unlike the perpendicular seating in gate valves, globe valve seating is parallel to the line of flow. All contact between seat and disc ends when flow begins. These are advantages for more efficient throttling of flow, with minimum wire drawing and seat erosion. The directly proportionate relation of size of seat opening to number of turns of handwheel, a distinctive feature of plug-type globe valves, permits close flow regulation. An operator can gauge the rate of flow by the number of turns of the wheel. Shorter disc travel - with fewer turns required to operate globe valves - saves considerable time and work - also wear on valve parts. Whatever wear occurs as the result of frequent or severe operation presents less of a maintenance problem than in gate valves. Seat and disc in most globe valves can be repaired without removing the valve from the pipe line. CONCLUSION: Globe valves, while not recommended where resistance to flow and pressure drop would be objectionable, are generally ideal for throttling, and preferable for frequent operation. Basic Angle Valve Design The angle valve effectively utilizes globe valve seating principle while providing for a 90 degree turn in piping. It is less resisting to flow than the globe valve it displaces. Requires fewer joints; saves makeup time and labor.
  5. 5. 5/29/2014 Lesson 30: Choosing the Right Valve 5/22 Gate Valve Seating Designs... Solid Wedge Disc The most widely used disc in gate valves - the solid wedge-shaped disc - with matching tapered body seating surfaces. Favored for its strong, simple design and single part. Can be installed in any position without danger of jamming due to misalignment of parts. Ideal for steam service, and well suited for water, air, oil, gas, and many other fluids. Most practical for turbulent flow because there's nothing inside to vibrate and chatter. Refacing of the tapered disc surfaces isn't easy, but there's little need for it is valve is used fully opened or fully closed. Might be subject to some sticking when subjected to extreme temperature changes where body contracts more than disc. For such conditions, Crane flexible wedge disc is recommended. Double Disc This parallel-faced double disc makes closure by descending between matching seats in valve body. As the valve is being closed, a lower spreader (or in some cases, a disc wedge) strikes a stop in the bottom of the body. Further closure brings the upper spreader into contact with the lower spreader so that the discs are forced outward against the seats. First opening movement releases discs, and continued operation raises them clear of seat openings. Widely used on water service, in waterworks and sewage disposal plants; also on oil and gas, in cross-country pipe lines. Generally unsuited for steam. Rapid expansion and high velocity of steam flow tend to vibrate loose internal parts in disc assembly,
  6. 6. 5/29/2014 Lesson 30: Choosing the Right Valve 6/22 hastening wear. Exposure of closed valve to rise in external temperature may cause dangerous increase in internal pressure, if non- compressible liquid is trapped between discs. Because discs and body seats are perpendicular and parallel, repairing or refacing to compensate for wear is easier than on a tapered wedge disc. Should be installed with stem above horizontal for best results. Many spreader mechanisms are subject to jamming when installed with stem below horizontal line. Their Service Characteristics Flexible Wedge Disc Developed especially to overcome sticking in high-temperature service with extreme temperature changes. The shape of the flexible disc can be likened to two wheels on a very short axle. The "axle" or spud at the center of the disc is amply strong to carry the two halves of the disc together at all times...and yet, it permits a degree of action between them. It is this "flexibility" that makes the disc tight on both faces over a wide range of pressures...prevents sticking during temperature changes, and assures minimum operating torque. Although each disc face can move independently of the other...up to two full degrees...the construction is one-piece. There are no loose parts to cause harmful vibration. Split Wedge Disc A 2-piece, wedge disc that seats between matching tapered seats in body. Spreader device is simple, and integral with disc halves. When closing, last turn of handwheel forces discs against the seats. When opening, the first turn releases the discs from the
  7. 7. 5/29/2014 Lesson 30: Choosing the Right Valve 7/22 seats. Seating Materials... Key to valve performance The seat and disc constitute the "heart" of a valve; do most of its work. The material from which these parts are made, therefore, becomes important. The tougher the service, the more severe the demand on seating. Valve manufacturers recognize this fact by providing a wider choice of seating materials as valves go up the pressure-temperature scale or are offered for more rigorous service. For relatively low pressure and temperatures and for ordinary fluids, seating materials are not a particularly difficult problem. Bronze and iron valves usually have bronze or bronze-faced seating surfaces, or iron valves may be all iron. Nonmetallic "composition" discs are available for tight seating on hard-to-hold fluids such as air or gasoline. As pressures and temperatures increase or as the service becomes severe, careful consideration must be given to many factors, no one which can be overemphasized to the detriment of others. Long, trouble-free life requires the proper combination of hardness, wear- resistance, resistance to corrosion, erosion, galling, seizing, and temperature. Nor does it follow that a satisfactory combination in one instance will serve equally well in all others. Type of valve is a limiting factor, too. Selection of seating materials for corrosive fluids, regardless of pressure-temperature, is almost endless. Included are many types of alloys, as well as linings or coatings of many kinds. Valve Catalog your best guide Safest policy in specifying seating materials is in close adherence to valve manufacturer's recommendations, usually found in catalogs, otherwise supplied on request.
  8. 8. 5/29/2014 Lesson 30: Choosing the Right Valve 8/22 Globe Valve Seating Designs.. Plug Type Disc Long taper with corresponding seat, giving a wide area of seating contact, makes the plug-type disc superior to all others for severe throttling service, such as blow-off, soot-blower, boiler feed. Because of wide seat bearing, most cuts and nicks by dirt, scale, and other foreign matter in flow are seldom big enough to cause leakage. Plug disc shape, in proper combination of metals for service, is most effective in resisting erosive effects of close throttling. Construction permits replacement of seat if necessary. Conventional (ordinary) Disc A good seating design for many not-too-severe services, but not for close throttling. Disc has relatively narrow contact with body seat - virtually a line bearing. This narrow metal area, in closely throttled high-velocity flow, is subject to erosion and wire-drawing. Deposit of particles of foreign matter on seat makes tight closure virtually impossible. Yet uniform deposit on seat, such as coking action in oil refineries, is more easily broken down by the narrow bearing. It makes a tight metal-to-metal contact easier than a wide seat. Seat and disc can be conveniently serviced.
  9. 9. 5/29/2014 Lesson 30: Choosing the Right Valve 9/22 Needle Point Disc and Seat Needle point valves are designed to give fine control of flow in small-diameter piping. Their name is derived from their sharp- pointed conical disc and matching seat. They come in globe and angle patterns, in bronze and steel, and find usage on steam, air, water, oil, gas, light liquid, fuel oil, and similar services. Stem threads are finer than usual so that considerable movement of stem is required to increase or decrease opening through seat. Usually, these valves have reduced seat diameter in relation to pipe size. Their Service Characteristic Composition Disc A useful design in bronze and iron valves for adaptability to many services and for quick repairs. Discs available in compositions suitable for steam, hot water, cold water, oil, air, gas, gasoline, and many other fluids. Disc change is quickly made with slip-on disc holder. Highly regarded for dependable, tight seating on hard-to-hold fluids such as compressed air. Flat face relatively "soft" disc seats against a raised crown in body. Small particles of foreign matter are imbedded in disc, preventing seat damage and leakage. Suited for all moderate pressure services except close regulating and throttling, which can rapidly cut out the disc.
  10. 10. 5/29/2014 Lesson 30: Choosing the Right Valve 10/22 Angle Valve Seating It is well to note and remember the angle valve when looking for globe valves. If there's a right angle turn in the line near where you need a valve, an angle pattern gives you important advantages. It's available with the same seating variations as shown here for globe valves: plug-type disc, conventional, and composition disc. Has considerably reduced turbulence, restriction of flow, and pressure drop because flow makes one less change of direction than in globe valve. Angle valve cuts down on piping installation time, labor, and materials, also reduces number of joints or potential leaks by serving as a valve and a 90 degree elbow. Disc-Stem Connections... important factor in valve selection In Gate Valves In a gate valve, the sole function of the stem is to raise and lower the disc. In doing its job, the stem should not be subject to corollary stresses and strains of service conditions on the disc. Thus, with gate valves, especially those used for higher pressure installations, a relatively loose disc-stem connection is desired. If the connection were rigid, any side thrust on the disc caused by pressure and flow, would readily be transmitted to the stem, and tend to strain and possibly bend it. A properly fitted loose connection relieves strain on the stem due to any lateral movement of the disc.
  11. 11. 5/29/2014 Lesson 30: Choosing the Right Valve 11/22 In Globe Valves The stem in a globe valve not only raises and lowers the disc, but also must help guide it squarely to its seat. Thus, unlike a gate valve, the globe valve disc-stem connection must be relatively close fitting to prevent any extreme lateral motion of the disc that would cause it to cock and seat improperly. But, once the disc and seat are joined, the disc must stop turning while seating is completed by the stem. This will avoid metal-to-metal friction between disc and seat that would be destructive to seating surfaces. The solution to this need is a swivel action in globe valve disc-stem connections, which permits true and tight seating without damage to seating surfaces. Variations in Stem Operations Although in many valve applications the type of stem operation makes little or no difference, in other cases it can be important. A simple example of the latter is the need for a self-indicator to show open or closed position, as in the case of rising stem valve, or, conversely, the need for a non-rising stem valve because of lack of head room. This shows how stem operating designs are adapted to service needs. Rising Stem with Outside Screw On both valves shown here, whether opened or closed, the stem threads always remain outside the valve body. They are not subjected to corrosion, erosion, sediment, or any elements in the line fluid that might damage stem threads inside the valve body. Being outside, they can be lubricated easily when necessary. Rising Stem with Inside Screw
  12. 12. 5/29/2014 Lesson 30: Choosing the Right Valve 12/22 This is the simplest and most common stem construction for gate, globe, and angle valves in the smaller sizes. Stem turns and rises on threads inside the valve. Position of handwheel indicates position of disc - opened or closed. Non-rising Stem with Inside Screw Generally used on gate valves only, this stem does not rise, but merely turns with handwheel. In turning, the stem threads raise or lower the disc. Since stem only rotates, packing wear is less. Ideal where head room is limited. Sliding Stem is Often Useful The sliding stem valve is useful where quick opening and closing are wanted. A lever takes the place of the handwheel, and stem threads are eliminated. Available in both gate and globe valves. Stuffing Box Designs Featured on CRANE Valves Stuffing box must effect a tight seal around the stem to retain pressure inside piping system. Stem must be tight without binding. Packing is subject to wear and must be periodically compressed and eventually replaced. 1. Packing Nut without Gland Used on low-pressure and small-size valves. With wheel and packing nut removed, this type is easier to repack than ordinary gland type on valves with small diameter stem. 2. Packing Nut with Gland Conventional type packing nut with loose gland. Gland has small lip at top edge so that it can be pried out with screwdriver tip if
  13. 13. 5/29/2014 Lesson 30: Choosing the Right Valve 13/22 jammed all the way down. 3. Bolted Gland Deep stuffing box with two-piece ball-type gland and flange with swing-type eye bolts. Construction maintains an even load on the packing and prevents binding on the stem even when the gland bolt nuts are pulled up unevenly. 4. Injection Type Add new packing with the twist of a wrench, even under full rated line pressure, and with the disc in any position! No need to backseat the disc. The specially designed ball check valve eliminates possibility of packing extrusion. When the packing reservoir is empty, simply back out the adjustment screw and insert a new pack stick. 5. Lantern Type Superior construction for larger-size high pressure-temperature valves. Cooling chamber with lantern spacer and three rings of packing below to wipe stem clean before it passes into the sealing rings above. Two-piece ball-type gland and flange with swing- type eye bolts. Bonnet and Bonnet Joint Characteristics ...of gate, globe, and angle valves
  14. 14. 5/29/2014 Lesson 30: Choosing the Right Valve 14/22 Which is best? In choosing valves, the service characteristics of the bonnet joint should not be overlooked. Bonnets and bonnet joints must provide a leakproof closure for the body. There are many modifications, but the three most common types are screwed-in bonnet, screwed union ring bonnet, and bolted bonnet. Screwed-in Bonnet The simplest and least expensive construction, frequently used on bronze gate, globe, and angle valves, and recommended where frequent dismantling is not needed. When properly designed with running threads, and carefully assembled, the screwed-in bonnet makes a durable pressure- tight seal, suited for many services. On modified steel valve designs such as the lip-seal valve with a weld around the periphery of the body-bonnet juncture, the screwed-in bonnet withstands even high pressures and temperatures. Screwed Union Ring Bonnet A good choice for quick dismantling and reassembly - yet a strong, well-reinforced joint. Convenient where valves need frequent inspection or cleaning - also for quick renewal or changeover of disc in composition disc valves. Separate union ring applies direct load on bonnet to hold a pressure-tight joint with body. Turning motion used to tighten ring is spent between shoulders of the ring and bonnet. Hence, the point of seal contact between bonnet and body is less subject to wear from frequent opening of the joint. Contact faces are less likely to be injured in handling. Union ring gives the body added strength and rigidity against internal pressure and distortion. While ideal on smaller-size valves, it is impractical on large sizes. Bolted Bonnet Joint A practical and commonly used joint for larger-size valves or for higher pressure applications.
  15. 15. 5/29/2014 Lesson 30: Choosing the Right Valve 15/22 Adaptable to all types of gasketing. Multiple bolting, with small diameter bolts, permits equalized sealing pressure without the excessive torque needed to make large threaded joints. Only small wrenches are needed. Has practically no limitation for size. Only the highest pressures and temperatures tax its capacity to permanently hold tight. Lip-Seal Bonnet Joint Crane's lip seal design features simplicity. The body and bonnet are screwed together until a firm metal-to-metal contact is made between the smoothly machined, flat surfaces on the shoulder of the bonnet and the top of the body. The shoulder of the bonnet is smaller in diameter than the mating area of the body, thus permitting the use of a fillet form of seal weld around the periphery of the connection. Dismantling is accomplished by grinding off the fillet weld and unscrewing the bonnet. The design makes possible compact, relatively lightweight valves ideal for high pressure-temperature services. Absolute tightness, full seating area, and freedom from bonnet joint maintenance are other advantages. CRANE Pressure-Seal Bonnet Joint Newest and most effective bonnet joint, developed by Crane, for sealing the highest pressures and temperatures, especially in steam service. Tightness of seal does not depend on nuts, bolts, and threads as in conventional bonnet joints. Instead, Crane Pressure- Seal bonnet joint utilizes line fluid pressure to seal the joint. The greater the pressure, the tighter the seal. The actual joint is inside the valve, and is sealed with a wedge-shaped seal ring. Internal fluid pressure acting on the entire underside area of the bonnet, is concentrated at the smaller contacting area of the wedge-shaped ring to make a pressure- tight metal-to-metal joint. Available in gate, globe, angle, check and stop-check valves.
  16. 16. 5/29/2014 Lesson 30: Choosing the Right Valve 16/22 Basic Check Valve Design The Swing Check...companion for gate valves Swing checks work automatically as shown here. But whether used in a horizontal line or vertical line for upward flow, they will not function properly unless installed with pressure under the disc. Flow through swing checks is in a straight line and without restriction at the seat, similar to a gate valve. This similarity in effect on flow is the reason for generally using swing checks in lines in combination with gate valves. The Lift Check...companion for globe valves Lift checks also operate automatically by line pressure. They should be installed with pressure under the disc. Like the globe valve with its indirect line of flow, the lift check is restricting to flow. For this reason it is generally used as a companion to globe valves. Basic Ball Valve Designs The advantages of quarter-turn ball valves are well established. Straight-through flow, minimum turbulence, low torque, tight closure and compactness are only a few of many reasons for their wide popularity among users. Reliable operation, easy maintenance and long-life economy justify their extensive application. Industrial, chemical, petrochemical, refinery, pulp and paper, gas transmission, water works and sewage, and power plants are utilizing ball valves where other types of valves have proven inadequate. Crane Co. manufactures a broad line of ball valves for practically any service requirement; listed below are basic designs.
  17. 17. 5/29/2014 Lesson 30: Choosing the Right Valve 17/22 Capsule types Both the Hydro Gem and the Gem Valve feature a top-entry capsule design providing easy "in-line" maintenance, if ever required. The Crane "GEM" ball valve can be readily and practically adapted to a variety of installations on gas, water, and oil lines where fluid temperature is reasonably constant. The nature of its construction together with the replaceable capsule assembly make this valve ideal for tight spot installations. The Buna N two-piece capsule encasing the ball can be replaced without removing the valve from the line with only a screwdriver or small wrench. This inexpensive bronze valve is available in small sizes with screwed or solder-joint ends. It is designed without a packing nut in sizes 3/4-inch and smaller, and with a packing nut in larger sizes. HYDRO GEM valves offer many of the same fine features as the Gem valve. However, to better meet the demands of "fluctuating temperature" applications, Hydro Gem valves feature a synthetic elastomer capsule compounded especially for water service. This elastoer...ethylene-propylene-terpolymer (commonly known as "EPT")...retains its resiliency and stability over a broad temperature range. All sizes have a bonnet gasket and packing box. Hydro Gem valves are an ideal choice for almost any water application within their pressure-temperature range. They are particularly suitable in water services subject to temperature fluctuations...and are unexcelled for use in hydronic heating/cooling systems. End entry type Crane TORK-SEAL ball valves are the low-cost dependable choice for tough applications in chemical, petroleum, and industrial installations. One-piece body coupled with end entry design virtually eliminates all potential leakage to atmosphere. Internally-loaded TFE (tetrafluoroethylene) seats, one on each side of the ball, are securely retained in the body by one or two threaded ferrules, depending on size. Unique stuffing box design utilizes a packing nut, spring washers, and a gland to maintain a sustained pressure on the packing...assures a tight stem seal. Available in a wide range of sizes in stainless steel, carbon steel or bronze...and with screwed, 150- pound flanged, or 300-pound flanged ends. Cartridge type Crane "Accesso" ball valves are excellent shutoff valves for steam, water, and oil, as well as for a wide variety of flammable and hazardous liquids and gases. They control the flow of a multitude of products in industrial and process piping in chemical plants,
  18. 18. 5/29/2014 Lesson 30: Choosing the Right Valve 18/22 petroleum lines, utility installations, power plants and general industrial plants. They feature cartridge type seating assemblies which simplify fast-in-line maintenance service. Furnished with screwed ends in stainless steel, carbon steel or bronze in sizes 1/4 through 2- inch. Basic Butterfly Valve Designs The Crane "MONARCH" butterfly valve incorporates the most desirable engineering features with the best suited materials into a valve that is efficient, durable, and reliable. Crane provides a selection of sizes from 2 through 24-inches with a choice of three body styles, molded-in or cartridge seats, five types of operators and a variety of component material combinations. Butterfly valves have widespread usage, and with an ever increasing number of new applications being determined, their popularity is rapidly increasing. In paper mills and cement mills, chemical and food processing plants, water filtration plants, petroleum product lines, air conditioning and water fact, practically anywhere there is a flow of fluid there is a use for Crane "MONARCH" valves. These valves are rated for temperatures up to 180°F and are bubble-tight at pressures up to 200 psi for 2 through 12-inch sizes --150 psi for 14 through 24-inch sizes. The Buna-N seat is scientifically dimensioned to give maximum resiliency under the seating land of the disc. Other seat materials also are available. This permits optimum disc impingement for greater seat tightness, without overstressing the liner. The disc edge is precision ground, finished and hand polished to assure long life and trouble-free operation. All Crane "MONARCH" butterfly valves are compact and space saving. They are easily installed in new piping or readily used as replacements in existing piping. Wafer Type Body The wafer type valve is designed for quick installation between pipe flanges. No gasket is needed because the molded-in seat is lapped over into a recess in both faces of the body ends. This portion of the seat is a labyrinth type of heavy multiple ribs of buttressed design and serves as a seal between the valve and pipe flanges. Bolt holes are provided in the body of valves 14-inch and larger to facilitate
  19. 19. 5/29/2014 Lesson 30: Choosing the Right Valve 19/22 alignment with pipe flanges. Wafer Lug Type Wafer lug type valves, except for their lugs completely around the body, are the same design as wafer type valves. In some lug type designs, the lugs are simply drilled to match ANSI (American National Standard Institute) 150-Pound Steel (and 125-Iron) drilling templates. Crane drills and taps the lugs so that when the valve is closed, upstream piping can be left intact while downstream piping is dismantled for cleaning, revamping, etc...or, if the valve is utilized for pipe-end applications, only one pipe flange is necessary. Two-Flange Type Body The two-flange type valve, except for body and seat design, is the same as the wafer type. The seat is not lapped over the body ends, and a gasket is required as a seal between the pipe flanges and body flanges. The Common Materials of Which Valves Are Made selection of valves starts here It pays to know the range of materials from which valves are usually made, and to understand the pressure, temperature, and structural limitations of each material. It may be highly unsafe to use materials for services beyond their recommended maximum. Valves commonly used in industry fall into the four general material groups shown below. Variants in each of these groups have individual service characteristics. Bronze
  20. 20. 5/29/2014 Lesson 30: Choosing the Right Valve 20/22 Crane Steam Bronze is widely used in valves and fittings for temperatures up to 450°F. It is an alloy of copper, tin, lead, and zinc. Crane Special Bronze is a high-grade copper-base alloy used in piping equipment for higher pressures and for temperatures up to 550°F. Iron Crane Cast Iron is regularly made in three grades - Cast Iron, Ferrosteel, and High Tensile Iron. These metals are recommended for temperatures up to 450°F. Cast Iron is commonly used for small valves having light metal sections. Crane Ferrosteel, stronger than cast iron, is used for valves having medium metal thicknesses. High Tensile Iron has even greater strength, and is used principally for large size castings. Malleable Iron Malleable Iron used in valves is characterized by pressure tightness, stiffness, and toughness, the latter property being an especially valuable one for piping materials subjected to stresses and shock. Steel Steel is recommended for high pressures and temperatures and for services where working conditions, either internal or external, may be too severe for bronze or iron. Its superior strength and toughness, and its resistance to piping strains, vibration, shock, low temperature, and damage by fire afford reliable protection when safety and utility are desired. Many different types of steel - cast, forged, alloy - are both necessary and available because of the widely diversified services steel valves perform. Ductile Iron
  21. 21. 5/29/2014 Lesson 30: Choosing the Right Valve 21/22 Crane Nodular Cast Iron, also known as ductile iron is cast iron with the graphite substantially in spherical shape and reasonably free of flake graphite. This results in a cast iron having high strength and good ductility. The corrosion resistance of nodular iron is approximately the same as that of gray iron. Strength is about 3 times greater. Stainless Steel Crane Stainless Steel Castings are heat treated for maximum corrosion resistance, high strength, and good wearing properties. Seating surfaces, stems, and discs of stainless steel are well suited for severe services where foreign materials in the fluids handled could have adverse effects. Stainless steel has excellent resistance to wear, seizure, galling erosion, and oxidation. How to Read Service Rating Marks Nearly all Crane products are designated by the general or primary pressure class such as "25-Pound," "100-Pound," "125-Pound," etc. These should not be construed as a recommendation for use of the product at those pressures. The designations are descriptive of a general product class and do not necessarily imply that all items within a given class...or that all sizes of a given product...are rated for the same primary service pressure. Recommended pressure ratings for Crane products are included on the catalog page or pages pertaining to those products and, practically all products excepts gas stops are marked with the recommended basic working pressure. If the product is marked with numerals not followed by a letter suffix, the marking denotes the basic steam pressure rating at the maximum temperature indicated on the page describing the product. If the marking consists of numerals followed by the letters G, L, O, S, or W, either individually or collectively, it denotes the gas, liquid, oil, steam, or water service pressure rating, respectively, at the maximum temperature indicated on the page describing the product. Valves with leather or composition faced discs are exceptions to the foregoing. These valves use bodies which are regularly marked with a basic steam rating...but the valves should be used only for services for which the type of disc facing is recommended. Test pressure markings, where used, are followed by the word "TEST".
  22. 22. 5/29/2014 Lesson 30: Choosing the Right Valve 22/22 Below are a few Serve Rating Marks: