The Expanding Reach of Plastic Valves
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BACK TO BASICS As seen in the Spring 2013 issue of M A G A … Z I N E The Expanding Reach of Plastic Valves Although plastic valves are sometimes seen as a Executive Summary BY TIM MORAN specialty product—a top choice of those who SUBJECT: Valves are manufactured in a make or design plastic piping products for industrial systems or wide array of thermoplastic materials who must have ultra-clean equipment in place—assuming these valves don’t have many general uses is short-sighted. In reality, with special properties. Designers have plastic valves today have a wide range of uses as the expanding come up with a variety of ways to use types of materials and good designers who need those materials new kinds of plastic valves. S P mean more and more ways to use these versatile tools. R I N KEY CONCEPTS: G 2 0 1 PLASTIC’S PROPERTIES • Thermoplastic materials 3 The advantages of thermoplastic valves are wide—corrosion, • Options in valve types V chemical and abrasion resistance; smooth inside walls; light A weight; ease of installation; long-life expectancy; and lower life- • What these valves can do L V cycle cost. These advantages have led to wide acceptance of E • Design considerations plastic valves in commercial and industrial applications such as M water distribution, wastewater treatment, metal and chemical A TAKE-AWAY: These valves are critical in G processing, food and pharmaceuticals, power plants, oil refineries harsh and challenging environments, but A and more. Z I perform well in many situations today. N E 1 ©2013 Valve Manufacturers Association. All rights reserved. Reprinted with permission. Plastic valves can be manufactured When designing piping systems and from a number of different materials considering the impact on valve place - used in a number of configurations. The ment and valve supports, an important most common thermoplastic valves are consideration in thermoplastics is ther - made of polyvinyl chloride (PVC), chlo - mal elongation. Stresses and forces rinated polyvinyl chloride (CPVC), that result from thermal expansion and polypropylene (PP), and polyvinylidene contraction can be reduced or eliminat - fluoride (PVDF). PVC and CPVC valves ed by providing flexibility in the piping are commonly joined to piping systems systems through frequent changes in by solvent cementing socket ends, or direction or introduction of expansion threaded and flanged ends; whereas, PP loops. By providing this flexibility and PVDF require joining of piping sys - along the piping system, the plastic tem components, either by heat-, butt- valve will not be required to absorb as or electro-fusion technologies. much of the stress (Figure 1). Ⅺ Figure 1. Elongation or contraction occurs when Thermoplastic valves excel in corro - temperature increases or decreases. Because thermoplastics are sensitive sive environments, but they are just as to temperature, the pressure rating of a useful in general water service because valve decreases as temperature rises. they are lead-free 1, dezincification- transparent to sunlight and can expose Different plastic materials have corre - resistant and will not rust. PVC and the fluid to UV radiation. While a natu - sponding deration with increased tem - CPVC piping systems and valves should ral, unpigmented formulation of PVDF perature. Fluid temperature may not be be tested and certified to NSF [National is excellent for high-purity, indoor the only heat source that can affect a Sanitation Foundation] standard 61 for applications, adding a pigment such as plastic valves’ pressure rating—maxi - health effects, including the low lead a food-grade red would permit exposure mum external temperature needs to be requirement for Annex G. Choosing the to sunlight with no adverse effect on part of design consideration. In some proper material for corrosive fluids can the fluid medium. cases, not designing for the piping be handled by consulting the manufac - Plastic systems have design chal - external temperature can cause exces - turer’s chemical resistance guide and lenges, such as sensitivity to tempera - sive sagging due to lack of pipe sup - understanding the effect that tempera - ture and thermal expansion and contrac - ports. PVC has a maximum service tem - ture will have upon plastic materials’ tion, but engineers can and have perature of 140°F; CPVC has a strength. designed long lasting, cost-effective maximum of 220°F; PP has a maximum Although polypropylene has half the piping systems for general and corrosive of 180°F; and PVDF valves can main - strength of PVC and CPVC, it has the environments. The major design consid - tain a pressure up to 280°F (Figure 2). most versatile chemical resistance eration is that the coefficient of thermal On the other end of the temperature because there are no known solvents. expansion for plastics is greater than scale, most plastic piping systems work PP performs well in concentrated acetic metal—thermoplastic is five to six times quite well in temperatures below freez - acids and hydroxides, and it is also that of steel, for example. ing. In fact, tensile strength increases suitable for milder solutions of most acids, alkalis, salts and many organic chemicals. Ⅺ Figure 2. The pressure and temperature differences between plastic materials PP is available as a pigmented or unpigmented (natural) material. Natu - ral PP is severely degraded by ultravio - let (UV) radiation, but compounds that contain more than 2.5% carbon black pigmentation are adequately UV stabi - 3 lized. 1 0 2 PVDF piping systems are used in a G N I R variety of industrial applications from P S pharmaceutical to mining because of E PVDF’s strength, working temperature N I and chemical resistance to salts, strong Z acids, dilute bases and many organic A G solvents. Unlike PP, PVDF is not degrad - A ed by sunlight; however, the plastic is M 1 E Lead Free refers to the wetted surface of pipe, fittings V and fixtures in potable water systems that have a L weighted average lead content ≤0.25% per the Safe A Drinking Water Act (Sec. 1417) amended 1-4-2011 and V other equivalent state regulations. 2 ©2013 Valve Manufacturers Association. All rights reserved. Reprinted with permission. This article could not cover all of the plastic materials, types in thermoplastic piping as tem - PLASTICS of valves, valve options and system requirements available perature decreases. However, RESOURCES impact resistance of most plastics today. However, it illustrates just how broad the market is decreases as temperature falls, and and what promise it holds. Today, there are many plastics brittleness appears in affected piping specialty distributors and knowledgeable plastic professionals that can materials. As long as the valves and help users discover how plastic valves and piping systems can meet or adjoining piping system are undis - exceed their needs. Three of those sources are the Plastic Pipe and Fittings turbed, not jeopardized by blows or Association (www.ppfa.org), International Association of Plastic Distribu - bumping of objects, and the piping is not dropped during handling, adverse tors (www.iapd.org) and Plastic Piping Institute (www.plasticpipe.org). effects to the plastic piping are mini - mized. ufactured by several U.S. and foreign solutions, chlorinated hydrocarbons TYPES OF THERMOPLASTIC VALVES companies in sizes 1/2 inch through 6 and petroleum oils. Ball valves, check valves, butterfly inches with socket, threaded or flanged PVC and CPVC ball valves, 1/2-inch valves and diaphragm valves are avail - connections. The true union design of through 2 inches, are a viable option able in each of the different thermo - contemporary ball valves includes two for hot and cold water applications plastic materials for schedule 80 pres - nuts that screw onto the body, com - where the maximum non-shock water sure piping systems that also have a pressing elastomeric seals between the service can be as great as 250 psi at multitude of trim options and acces - body and end connectors. Some manu - 73°F. Larger ball valves, 2-1/2 inches sories. The standard ball valve is most facturers have maintained the same ball through 6 inches, will have a lower commonly found to be a true union valve laying length and nut threads for pressure rating of 150 psi at 73°F. design to facilitate valve body removal decades to allow for easy replacement Commonly used in chemical con - for maintenance with no disruption of of older valves without modification to veyance, PP and PVDF ball valves (Fig - connecting piping. Thermoplastic check the adjoining piping. ures 3 and 4), available in sizes 1/2- valves are available as ball checks, Ball valves with ethylene propylene inch through 4 inches with socket, swing checks, y-checks and cone diene monomer (EPDM) elastomeric threaded or flanged-end connections checks. Butterfly valves easily mate seals should be certified to NSF-61G for are commonly rated to a maximum with metal flanges because they con - use in potable water. Fluorocarbon non-shock water service of 150 psi at form to the bolt holes, bolt circles and (FKM) elastomeric seals can be used as ambient temperature. overall dimensions of ANSI Class 150. an alternative for systems where chem - Thermoplastic ball check valves rely The smooth inside diameter of thermo - ical compatibility is a concern. FKM on a ball with a specific gravity less plastic parts only adds to the precise also can be used in most applications than that of water, so that if pressure control of diaphragm valves. involving mineral acids, with the is lost on the upstream side, the ball Ball valves in PVC and CPVC are man - exception of hydrogen chloride, salt will sink back against the sealing sur - face. These valves can be used in the Ⅺ Figure 3. A flanged ball valve attached to a tank Ⅺ Figure 4.