Michael F. Crawley, Chief Executive of Macawber Engineering, Inc. USA presents a new concept in valve design for operating reliability. The Inflatek Valve's® unique seat sealing method heralds a new concept in valve design. A flexible, inflatable seat which is designed to entrap particles at the seat completely overcomes the main source of the valve seat wear. The valve was designed in the late '70's, and since then has seen diverse application in many industries with a present day valve installation population of some 7,000 valves. In recent times, the valve has been applied to retrofit and to new system designs in the chemical processing industry where conventional valve designs have not met operational or reliability requirements. The unique inflatable sealing action has been developed to satisfy applications in which a) Abrasive materials such as sand, coke breeze, and ground glass can be handled without coat wear. b) Pressure differentials with abrasive materials in fluid media may be sealed with up to 18 bar pressure differential and with full vacuum service. c) Perform upon applications with media temperatures up to 660°F. d) Perform in applications comprising combinations of the above conditions. In addition, in most applications, the valve may close and seal through a static column of powder or granular material in one action. The paper describes the valve design and its performance in a wide range of duties, and sets out to challenge the concepts of future valve designs utilizing the innovative principle of inflatable valve seats. Introduction This paper describes a unique valve concept which has been proven to demonstrate remarkable characteristics of reliability and wear resistance operating with abrasive bulk materials and pressure differentials. The device, known as the Inflatek Valve® was developed in the '70's and registered at the United States patent office. It incorporates a unique seat sealing method. The valve seat is a flexible and inflatable heavy membrane which is designed to entrap particles at the seat, to prevent their movement under the influence of a pressure differential, and therefore overcome the main cause of wear in valves handling bulk materials or dirty gases containing particulate. Although the valve introduces a new concept in seat sealing technique, it has been widely applied in many industries. The manufacturer claims 7,000 installations throughout the world since its introduction to North America in 1978 in diverse applications such as controlling filling of pressure vessels with hot bottom ash at 1200°F and supporting a pressure differential of 6 bar, to controlling filling of a pressure/vacuum chamber with magnesium powder. Many applications of the Inflatek Valve® are in retrofit situations where conventional valves have failed to provide reliable operations in pressure differential applications. This is typical of situations in which closing member design or seat design allows particulate movement across the seat face to cause accelerated wear. This is a situation common to conventional valves applied beyond their application ability normally for reasons of first cost economy. Fig. 1: The Incomparable Inflatek Valve® Valve Design Objectives The valve was designed to achieve two main objectives: a) To provide minimal or no seat wear when handling abrasive bulk materials, and closing action to support a pressure differential. b) To provide a closing and sealing action in one motion through a static or moving column of bulk materials. Subsequent development of the valve allowed additional objectives to be achieved which were: c) Achieve the above objectives when operating in applications at a constant temperature of 660°F. d) Achieve the above objectives when operating with both pressure and vacuum differentials in the same operating cycle. e) Provide a snap-open characteristic to the closing member of the valve for high gas pressure exhaust applications. f) Flow regulation with auto positioning capability in addition to flow stop requirements. Additional design objectives relating to valve performance and practical considerations were incorporated: g) Unrestricted flow through the valve when in the open position. h) Easy inspection and maintenance. i) Open choice of valve operators for any valve application. j) Wide range of construction materials for media compatability. k) Wide range of seal membrane materials for media compatability. l) Very low maintenance costs. The main components of the valve, i.e., dome, casting, top plate, do not require replacement or repair for several years. The inflatable seal is often only replaced once per year, or every two years, and is a low cost item. The history of valve design objectives implemented by the manufacturer was influenced by the initial application duty of the Inflatek Valve®. During its first years of introduction, the Inflatek Valve® was exclusively applied to high pressure pneumatic conveying systems in which the majority of materials handled were abrasive, such as coke breeze, lump coal, or sand, and in which pressure differentials were up to 7 bar. Recently the valve began to see application opportunities within the general valve market where the evident superior ability of the sealing technique became noticed. General applications in the chemical processing industry have subsequently caused the latter design objectives to be adopted with consequent strengthening of application capability. Valve Design The valve design is a masterpiece of simplicity. The closing member is a segment of a sphere (dome) with extended arms mounted to shafts (see Fig. 2). The shaft is driven 90° by an actuator which allows the crank-mounted dome to rotate entirely away from the inlet port of the valve body. Passage through the valve is therefore totally unobstructed.

In the closed position, the dome sits concentrically beneath the inlet port beneath which the inflatable seal assembly is positioned. The inflatable seal, which is a complete ring of an elastomer or rubber approximately 3/4" to 1" wide, covers the periphery of the dome. A controlled gap of about 1mm between the face of the dome and the face of the inflatable seal (seat) allows the dome to rotate into and away from the closed position. Particles from the media entering the valve are allowed to pass or remain between the seal and the surface of the dome. Closing the Inflatek Valve® automatically sequences the seal to inflate by initiating a limit switch when the dome drive shaft completes a 90° rotation to the closed position. Seal inflation is achieved by introducing compressed air or other gas through a small plenum behind the sealing ring. With sealing air pressures of 25 psi or 20% higher than the pressure differential across the valve closing member are applied, the seal inflates and engages the periphery of the dome component. Small particles that enter the gap between the seal face and the dome surface are entrapped by the expanding face of the rubber seal to prevent their movement and subsequent wear to the seat (see Fig. 3).

This technique of entrapping particles between the seat has been proven to considerably reduce the valve seat wear even when performing with the fine abrasive powders such as ground glass and coke breeze. The pneumatic seal and its operating action provides an additional benefit: As wear does occur on the seal face or the dome component, the expanding seal provides wear compensation automatically until a wear limit is reached. The wear limit is considerably greater than any other valve design. So confident are the manufactures of this unusual feature that they provide a 1 million cycle frequency between seal inspections on approved applications. The pneumatic seal or inflatable seat is a masterpiece of simple mechanical design. The seal component is a continuous ring with a special profile that provides both correct location and effective anchoring. There are no special fasteners or adhesives to complicate the process of assembly or replacement. The seal ring is beneath the top plate of the valve so that when the valve is used in its preferred direction of flow mode, the seal is completely protected from the flow of media through the valve. The manufacturer has developed an impressive array of seal materials utilizing various rubber compounds and elastomers to ensure temperature and chemical compatibility with media passing through the valve (Table 1). Table 1: Seal materials and temperature applications Abbreviation Technical Nomenclature Common Name Service Temp °F °C min max min max CR Chloroprene Rubber Rubber -65 230 -54 110 NBR Nitrile Butadiene Rubber Buna N/Nitrile -65 240 -54 116 *NR Natural Rubber Rubber -65 180 -54 82 *PGR Natural Rubber Pure Gum Rubber -65 180 -54 82 CIIR Chloro-Isobutylene Isoprene Rubber Chlorobutyl -65 250 -54 120 CSM Chloro-Sulfonyl Polyethylene HypalonTM -65 250 -54 120 EPDM Ethylene Propylene Diene Monomer Ethylene Propylene Rubber (NordelTM, RoyaleneTM) -65 300 -54 149 FPM/ FKM Fluorocarbon Elastomer VitonTM FluorelTM -40 400 -40 204 AFMU Tetrafluoro-ethylene Resin TeflonTM -120 450 -85 232 SI Dimethyl Polysiloxane Silicon -160 500 -107 260 One of the most impressive innovations of this remarkable valve is the use of water for cooling purposes in high-temperature applications. It was originally regarded by the valve designers to be a disadvantage to require an additional utility to the valve to enable its operation for high temperature duties. However, the choice between exotic materials of construction with experimental polymers for the seal over the addition of cooling channels and additional utility connections was not difficult. Water cooling has proven to be a wise and effective choice enabling a simple, effective and low-cost valve solution for some of the most demanding applications in the industry. Two temperature zone design steps are offered to ensure economic targeting of the product (see Fig. 4). Up to 355°F, the valve is provided with a water-cooling channel around the pneumatic seal area within the top plate. Up to 660°F temperature duty, the addition of a water-cooled dome component is provided. The water is introduced through a water channel in one shaft axis to the supporting leg of the dome, through the dome in which a chamber is provided, and exiting the valve in the same way through the other shaft, an unusual but simple and effective solution. The Inflatek Valve® is widely used in such high-temperature applications as ash handling for utilities and industrial coal-fired boiler plants, as well as many high-temperature chemical processes.

The simplicity and robustness of the valve and its shaft drive configuration allows any kind of type of valve actuator to be applied. This versatility has allowed the valve to be used in applications to solve special problems such as: Flow regulation by positioning the dome closing member as required by modulated signal from down-stream processes, added to the standard function of closing and sealing against substantial pressure differentials. Snap-open action to minimize gas velocities through the valve when operating with high-pressure exhaust applications, again added to the standard function of closing and sealing against substantial pressure differentials. This application has been satisfied for high-temperature dust laden gasses in which water cooling has been applied to both the valve sealing chamber and the dome component. The manufacturer has taken an unusual approach to the valve market with their unique design they have registered, packaging the features into a range of standard specifications with standardized variations in an attempt to seek out a volume market. They have taken the position of valve problem solvers with much of their market arising from retrofit situations and newly-designed applications in which "conventional" valves appear to be inadequate for reasons of temperature duty, abrasive media, or high pressure differential, or all three. The marketing philosophy appears to have worked well considering a first year sales volume of $1 million in 1992 without any sales promotion, and in a relatively depressed economy. Undoubtedly this good result was somewhat attributed to the vast installation reference list available to the manufacturer before they launched into the semi-special valve market with a new and independent product. The company offers a comprehensive range or sizes from 2" to 20", with all international connection standards available. The valves are manufactured at a facility possessing an ASME National Board license for pressure vessels. Considering the duty performance of the Inflatek Valves®, the manufacturing skills for pressure vessels are appropriate for the quality requirement of this new valve. Application Diversity The application capability of the basic valve design is unusually wide for many reasons stated earlier which are summarized as follows: Abrasive Media: Abrasive slurries, bulk powders, granules and dust-laden gasses cause rapid seat erosion and ineffective closure in conventional valve designs. The inflatable seal and its automatic wear compensation feature appears to overcome the wear problems associated with abrasive media. Pressure Differentials: Also cause accelerated seat wear in conventional valve designs, even though hardened seats may be used. Pressure differential causes untrapped particles in hard seat valves to move across the seat at high velocity which erodes hard seats and commences the wear process. The inflatable seal effectively entraps the particles and prevents particle movement and therefore wear. High Temperature: Thermal expansion prevents consistent valve seat action in hard seat valves. The inflatable seal provides seal action compensation throughout the temperature range. Valve performance on media temperature up to 700°F has been achieved. Close and Seal: The displacement action of the dome component and its spherical shape rotating within the valve housing allows closure through a solid column of bulk materials, followed by the seat sealing action of the inflatable seal. A New Challenge to Valve Design Philosophy With an impressive array of 7,000 tough installations, we should seriously consider the new philosophy of valve seat design represented by the Inflatek Valve®. Metal seats have always suffered from varying rates of wear, depending upon application and duty. The inevitable conventional wisdom concerning solutions to high-wear rates has been to provide tougher or harder seat materials, or exotic designer materials to tackle abrasion, temperature, and pressure differential. The philosophy has been to treat the symptom of the problem which is erosion from particulate movement across the seat. The Inflatek Valve® is the first valve that treats the cause of the problem. Entrapping particles at the seat and preventing their movement under the influence of a pressure differential is a unique approach to the problem. Evidence suggests that this philosophy is not only here to stay, but if we are to judge by the Inflatek Valve's® success, a technique we are likely to see a lot more of in valves and other mechanisms. Comparison with Conventional Valve Designs To place the Inflatek Valve® into the general family of valves now available, a comparison with conventional class valves is useful (see Table 2). The comparison is non-specific in terms of any single application study, but it does serve to provide a general representative comparison using general industry experience with all valve types. The Inflatek Valve® appears to provide application superiority against all conventional classes of valves. Table 2: Comparison with conventional valves and the Inflatek Valve for applications ability and general performance. Butterfly Valve Cone Valve Knife Gate Vee Ball Ball Valve Inflatek Valve Close and seal through static head of bulk materials No No No No No Yes Support pressure differential up to 1 bar Yes Yes No Yes Yes Yes Support pressure differential up to 14 bar No No No No Yes Yes Temperature capable to 660°F No No No No Yes Yes Good performance with abrasive materials No No No No No Yes Automatic compensation for wear No No No No No Yes Unobstructed flow through valve No No Yes Yes Yes Yes Add to this the manufacturer's aggressive, but apparently well-timed guarantee of one million cycles between inspections, and we have a new approach to valving that needs careful attention. The special advantages of the Inflatek Valve® are, however, available with an apparent disadvantage, and that is price. The conventional valve classes are lower in price, or as we say "first cost". However, if we adopt modern accounting philosophies for plant and equipment investment requirements, and consider life cycle cost, the low wearing and problem solving reputation of the Inflatek Valve® may well place this new and exciting product at the top of the list on all counts. Appendix: Examples of Inflatek Valve® Installations Valve Size Media Name Temperature °F Pressure Difference psig Operating Frequency cycles/h Owner Date of Installation Process 4" Sand 150 40 30 Harrison Steel 1980 Pneumatic Conveyor 8" Ash 660 60 60 Delco Remy 1978 Pneumatic Conveyor 8" TiO2 160 50 60 Ace Hardware 1983 Pneumatic Conveyor 8" Fructose 212 40 60 Pfizer 1988 Pressure / Vaccum Let Down 8" Rice Ash 335 30 90 Argi Electric 1985 Pneumatic Conveyor 4" Fly Ash 396 40 60 Reeves Bros. 1983 Pneumatic Conveyor 4", 6", 8", 10", 12" Alumina 180 60 30-120 Alcoa 1980 Retrofit Pneumatic Conveyor 8" Sugar / Dextrose 112 40 60 Allen Sugar 1991 Pneumatic Conveyor 8" Resin Powder 180 50 60 B.F. Goodrich 1984 Pneumatic Conveyor 8" SS Ultranox Crystal 200 50 60 General Electric 1987 Pneumatic Conveyor 8", 12" Lead Concentrate 396 60 15 Boliden Metals 1988 Pneumatic Conveyor 4" Ilmenite 396 60 60 Nord Rutile 1986 Pneumatic Conveyor 8" Litharge 200 50 60 Ferro Ind. 1990 Pneumatic Conveyor 8" Pebble Lime 180 40 60 First Miss Steel 1990 Pneumatic Conveor 8" Bottom Ash 396 30 60 Ford Motor Co. 1985 Pneumatic Conveyor 8" Coke Breeze 212 40 30 General Motors 1981 Pneumatic Conveyor 8" Paper Ash 535 30 60 Herman Bogot 1982 Pneumatic Conveyor 8" Bottom Ash 200 40 60 Galaxy Carpets 1982 Pneumatic Conveyor 8" Coke Breeze 200 50 60 J.I. Case 1980 Pneumatic Conveyor 8" Dolomite 212 35 120 Latrobe Steel 1991 Pneumatic Conveyor 8" Carbon 200 40 60 L.T.V. Steel 1987 Pneumatic Conveyor 8" Bottom & Flyash 535 40 100 Mallinckrodt 1983 Pneumatic Conveyor 8" Bottom Ash 396 50 120 Minnesota Corn 1983 Pneumatic Conveyor 8" Copper Concentrate 212 60 60 P.T. Inco 1990 Pneumatic Conveyor Retrofit 8" Bottom & Flyash 535 50 90 State of Illinois 1981 Pneumatic Conveyor