Elastic seat gate valve

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Introduction to elastic seat gate valves: The moving part of an elastic seat gate valve is the gate, whose movement direction is perpendicular to that of the fluid. Such valves can only be operated in the fully open or fully closed position; they cannot be used for regulation or throttling. The gate has two sealing surfaces. In the most common design of gate valves, these two sealing surfaces are wedge-shaped; the wedge angle varies depending on the valve parameters, usually being 50 degrees, and it is 2°52'''' when the temperature of the medium is not high. The gate of a wedge-type gate valve can be made as a single piece, known as a rigid gate ； It is also possible to create a gate that can undergo slight deformation, in order to improve its workability and compensate for any deviations in the angle of the sealing surface that occur during processing; such a gate is known as an elastic gate. Elastic seat gate valves are also known as lift stem gate valves (also called visible stem gate valves). Typically, a trapezoidal thread is present on the lift rod; through the nut at the top of the valve and the guide groove on the valve body, rotational motion is converted into linear motion, that is, the operating torque is transformed into an operating thrust. When the valve is opened, the flow path is completely unobstructed when the lift height of the gate plate equals 1:1 of the valve’s diameter; however, this position cannot be monitored during operation. In actual use, the apex of the valve stem is used as a reference point – that is, the position at which it can no longer be moved – and this is considered its fully open position. To account for locking due to temperature changes, it is common to turn the valve to its full-open position and then reverse it by 1/2–1 turn as the position for a fully open valve. Therefore, the fully open position of the valve is determined by the position of the gate (i.e., its travel). I. General Requirements 1.1 The specifications and categories of elastic seat gate valves shall meet the requirements of the pipeline design documents. 1.2 The model of the elastic seat gate valve shall indicate the relevant national standard number requirements. If it is a corporate standard, relevant specifications for the model should be indicated. 1.3 The operating pressure of the elastomeric seated gate valve should be ≥ the operating pressure of the pipeline; provided that it does not affect the price, the pressure that the valve can withstand should be higher than the actual operating pressure of the pipeline ； On either side of a resilient seated gate valve when it is closed, it should be able to withstand 1.1 times the working pressure of the valve without leaking ； With the valve open, the valve body shall be able to withstand a pressure twice the working pressure of the valve. 1.4 The manufacturing standards for elastic seat seal gate valves shall specify the corresponding national standard numbers; if it is a corporate standard, the relevant corporate documents shall be attached to the purchase contract. Valves of this type should generally be installed horizontally in pipelines. II. Specifications for elastic seat gate valves 2.1 The material of the valve body should be mainly ductile iron, cast steel, stainless steel, or 316L; the grade of the material as well as the actual physicochemical test data of the iron should be specified. 2.2 Valve stem material: stainless steel valve stems (2CR13) are preferred; for large-diameter valves, valve stems with a stainless steel core should also be used. 2.3 The material of the nut is cast aluminum brass or cast aluminum bronze, with hardness and strength both greater than those of the valve stem. 2.4 The material of the valve stem bushing shall have a hardness and strength that are not greater than those of the valve stem, and it shall not cause electrochemical corrosion with the valve stem and valve body when exposed to water. 2.5 Material of the sealing surface: ① There are various types of elastic seat gate valves, and the sealing methods as well as material requirements vary accordingly ； ②For ordinary wedge-type gate valves, the material of the copper ring, its fixing method, and the grinding method should all be specified ； ③Physical, chemical, and hygiene test data of the rubber-lined material used in the elastic seat seal gate valve ； 2.6 Valve stem packing ① Since elastic seat gate valves in piping systems are usually not opened and closed frequently, it is required that the packing remain inactive for several years, do not age, and maintain its sealing properties over time ； ②The valve shaft packing should also maintain good sealing performance under frequent opening and closing ； ③Given the above requirements, the valve shaft packing is designed to remain unchanged for life or for over a decade ； ④If the filler needs to be replaced, the design of the pneumatic valve should take into account measures for replacement under water pressure. III. Operating mechanism of elastomeric seat gate valves 3.1 The opening and closing direction when operating an elastomeric seat gate valve shall always be in a clockwise direction to close it. 3.2 Due to the pneumatic valves in the piping system, which are often operated manually, the number of operations should not be excessive; even for large-diameter valves, this should remain between 200 and 600 rotations. 3.3 To facilitate operation by a single person, under the working conditions of a plumber, the maximum opening and closing torque should be 240 N-m. 3.4 The operating end of the elastomeric seated gate valve should be equipped with square tenons, with standardized dimensions, and face downward so that it can be operated directly from the ground. Valves with wheels are not suitable for underground piping systems. 3.5 Display panel for indicating the degree of opening and closing of the elastomeric seat gate valve: ① The scale lines indicating the degree of opening and closing of the elastomeric seat gate valve should be cast on the gearbox cover or on the housing of the display panel after direction change; they must all face downward. The scale lines are coated with fluorescent powder to ensure visibility ； ②In cases where proper management is ensured, the material for the dial needle can be stainless steel plate; otherwise, painted steel plate should be used. Aluminum sheet must not be used for this purpose ； ③The dial needle is prominent and firmly fixed; once the opening and closing adjustment is accurate, it should be locked with rivets. 3.6 If the elastomeric seated gate valve is buried deep, and the distance between the operating mechanism and the display panel from the ground is ≥1.5 m, an extension rod should be provided and fixed securely, so that it can be observed and operated from the ground. In other words, the operation of opening and closing valves in the pipeline network should not be carried out by going down into the well. IV. Performance Testing of Elastic Seat Gate Valves 4.1 When valves of a certain specification are manufactured in bulk, an authoritative institution should be commissioned to conduct tests on the following performance parameters: ① The opening and closing torque of the valve under working pressure ； ②Number of consecutive opening and closing cycles under working pressure that can ensure a tight seal of the valve ； ③Detection of the flow resistance coefficient of valves under pipeline water conveyance conditions. 4.2 Before leaving the factory, the valve shall undergo the following tests: ① With the valve in the open position, the valve body shall be subjected to an internal pressure test equal to twice the working pressure of the valve ； ②With the valve closed, each side is subjected to 1.1 times the working pressure of the valve, with no leakage ； However, for butterfly valves with metal seals, the leakage rate is also no greater than the relevant requirements. V. Internal and external anti-corrosion treatment for elastomeric seated gate valves 5.1 On the interior and exterior of the valve body (including the gearbox), sandblasting should be carried out first to remove rust, followed by the application of electrostatic spraying of non-toxic powdered epoxy resin in a thickness of at least 0.3 mm. When it is difficult to use electrostatic spraying with non-toxic epoxy resin for extra-large valves, similar non-toxic epoxy paint should be applied by brushing or spraying. 5.2 The interior of the valve body as well as all parts of the valve disc must be fully protected against corrosion; they should not rust when immersed in water, and no electrochemical corrosion should occur between the different metals ； Secondly, the smooth surface reduces water resistance. 5.3 For the sanitary requirements of epoxy resin or paint used for anti-corrosion inside the valve body, test reports from relevant authoritative agencies shall be provided. The chemical and physical properties must also meet the relevant requirements. VI. Packaging and Transportation of Elastic Seat Gate Valves 6.1 Light blocking plates should be installed on both sides of the valve to secure it in place. 6.2 Valves of medium and small diameter should be tied with straw ropes and transported in containers. 6.3 Large-diameter valves also come with a simple wooden frame for solid packaging, to prevent damage during transportation. VII. Instruction Manual for Elastic Seat Gate Valves. Pneumatic gate valves are types of equipment, and the following relevant data should be specified in their instruction manuals: Valve specifications ； Model ； Work stress ； Manufacturing standards ； Valve body material ； Valve stem material ； Sealing material ； Valve stem packing material ； Material of valve stem bushing ； Internal and external anti-corrosion materials ； Operation start direction ； RPM ； Opening and closing torque under working pressure ； Name of the manufacturing plant ； Date of manufacture ； Factory serial number ； Weight ； Bore diameter, number of holes, and center hole spacing of the connection flange ； Indicate the control dimensions of length, width, and height in a graphical manner ； Valve flow resistance coefficient ； Effective opening and closing cycles ； Data related to the factory testing of valves, as well as precautions for installation and maintenance. VIII. Summary of standards for elastomeric seated gate valves: Standard number ANSI/NFPA T 3.21.4 R2-2000 – Pneumatic valves; NFPA/T 2.6.1 R2-2000 – Supplement: Pressure ratings for hydraulic components. Test fatigue and determine the pressure values of hydraulic and pneumatic valves with metal housings. BS 4151-1967: Method for the evaluation of pneumatic valve positioners with an input signal of 3 to 151 b/in pressure gauges. IX. Parameter Definitions 9.1 Nominal diameter: also known as mean outside diameter, it is denoted by the symbol DN; it represents the standard size for various pipes and piping fittings. Tubes and piping fittings of the same nominal diameter can be connected to each other, allowing for interchangeability. It is not the actual outer or inner diameter of the pipe; although its value is close to or equal to the pipe’s inner diameter, the nominal diameter (also known as nominal bore or nominal size) is used to standardize the connection dimensions of tubes and fittings. For example, welded steel pipes can be classified by thickness into thin-walled pipes, ordinary pipes, and thick-walled pipes. Its nominal diameter is neither the outer diameter nor the inner diameter, but rather a nominal size that is close to the inner diameter of ordinary steel pipes. For each nominal diameter, there is a corresponding outer diameter, while the inner diameter value varies depending on the thickness. The nominal diameter can be expressed in metric mm or imperial inches. Piping fittings are also indicated by nominal diameter, with the same meaning as welded pipes. 9.2 Nominal pressure: (Nominal pressure), denoted by the symbol PN, refers to the maximum operating pressure allowed when the component is used at a certain temperature. For control valves with carbon steel bodies, it refers to the maximum operating pressure permitted for use at temperatures below 200°C ； For cast iron valve bodies, it refers to the maximum operating pressure permitted for use at temperatures below 120°C ； For control valves with stainless steel valve bodies, it refers to the maximum operating pressure permitted for use at temperatures below 250°C. As the operating temperature rises, the pressure resistance of the valve body decreases. For example, a carbon steel control valve with a nominal pressure of 6.4 MPa (PN64) has a pressure resistance of 5.2 MPa at 300°C, 4.1 MPa at 400°C, and 2.9 MPa at 450°C. Therefore, the determination of the nominal pressure of a control valve must take into account not only the maximum operating pressure but also the maximum operating temperature and the material properties, rather than simply requiring that the nominal pressure be higher than the operating pressure.