SIST EN 13774:2014
(Main)Valves for gas distribution systems with maximum operating pressure less than or equal to 16 bar - Performance requirements
Valves for gas distribution systems with maximum operating pressure less than or equal to 16 bar - Performance requirements
This European Standard deals with metal isolating valves used for gas distribution systems with maximum operating pressure up to 16 bar, and which operate with fuel gases of the first, the second and the third family, in accordance with EN 437. The types of isolating valves to be considered are: plug and ball valves, gate valves, globe valves and butterfly valves. This standard does not apply to: - valves for domestic installations; - safety type pressure relief valves; - wellhead valves. In the case of power operated valves, the requirements for the power source are not covered by this European Standard. The valves covered in this European Standard operate in the following classes of temperature: - - 10 °C to 60 °C; - - 20 °C to 60 °C; - the range is stated by the purchaser for special design. This European Standard gives additional requirements to the relevant products standards. (See Annex B.) In case of contradictions between the standards mentioned in Annex B and this European Standard, EN 13774 prevails.
Armaturen für Gasverteilungssysteme mit zulässigen Betriebsdrücken kleiner oder gleich als 16 bar - Anforderungen an die Gebrauchstauglichkeit
Diese Europäische Norm gilt für Absperrarmaturen aus Metall, die in Gasverteilungssystemen mit einem höchsten Betriebsdruck von bis zu 16 bar verwendet werden und die mit Brenngasen der ersten, zweiten und dritten Familie nach EN 437 betrieben werden.
Die zu berücksichtigenden Bauarten von Absperrarmaturen sind: Kegel- und Kugelhähne, Schieber, Absperrventile und Klappen.
Diese Norm gilt nicht für:
- Armaturen für die Hausinstallation;
- Sicherheitseinrichtungen gegen Drucküberschreitung;
- Bohrkopfarmaturen.
Für kraftbetätigte Armaturen sind die Anforderungen an die Energieversorgung nicht in dieser Europäischen Norm festgelegt.
Armaturen nach diesem Dokument arbeiten in den folgenden Temperaturklassen:
- –10 °C bis 60 °C;
- –20 °C bis 60 °C;
- für Sonderausführungen wird der Temperaturbereich vom Käufer angegeben.
Diese Europäische Normenthält zusätzliche Anforderungen gegenüber den einschlägigen Produktnormen.
Bei Widersprüchen zwischen den vorgenannten Normen gilt diese Norm vorrangig.
Appareils de robinetterie pour les systèmes de distribution du gaz avec une pression maximale de service inférieure ou égale à 16 bar - Exigences de performance
La présente Norme européenne s'applique aux robinets d'isolement métalliques utilisés pour les systèmes de distribution du gaz avec une pression maximale de service jusqu’à 16 bar inclus, et fonctionnant avec des gaz combustibles de la première, de la seconde et de la troisième famille conformément à l'EN 437.
Les types de robinets d'isolement à prendre en compte sont les robinets à tournant sphérique, cylindrique et conique, les robinets-vannes, les robinets à soupapes et les robinets à papillons.
La présente norme ne s'applique pas aux :
- appareils de robinetterie destinés aux installations domestiques ;
- soupapes de sécurité ;
- robinets de tête de puits.
Dans le cas d’appareils de robinetterie motorisés, les exigences du moteur ne sont pas couvertes par la présente norme.
Les appareils de robinetterie auxquels s'applique cette norme, fonctionnent dans les classes de températures suivantes :
- - 10 °C à 60 °C ;
- - 20 °C à 60 °C ;
- la plage est établie par le client pour une conception spéciale.
La présente Norme européenne définit des exigences supplémentaires pour les normes de produits citées en références.
En cas de contradiction avec les normes mentionnées ci-dessus, la présente norme prévaudra.
Ventili za plinske razdelilne sisteme z največjim delovnim tlakom, manjšim ali enakim 16 bar - Zahteve glede uporabnosti
Ta evropski standard obravnava kovinske izolirne ventile, ki se uporabljajo za plinske razdelilne sisteme z največjim delovnim tlakom do 16 barov in ki delujejo z gorivnimi plini prve, druge in tretje družine, v skladu s standardom EN 437. Vrste obravnavanih izolirnih ventilov so: ventili s svečko in krogelni ventili, zasuni, zaporni ventili in zaporne lopute. Ta standard se ne uporablja za: – ventile za gospodinjske napeljave; – varnostne razbremenilne ventile; – ventile za ustja vrtin. V primeru ventilov s pogonskim mehanizmom zahteve za vir napajanja niso zajete v tem evropskem standardu. Ventili iz tega evropskega standarda delujejo v naslednjih temperaturnih razredih: – –10 °C do 60 °C; – –20 °C do 60 °C; – obseg, ki ga navede dobavitelj za posebno izvedbo. Ta evropski standard vsebuje dodatne zahteve za ustrezne standarde za proizvode (glej dodatek B). V primeru neskladij med standardi iz dodatka B in tem evropskim standardom ima prednost standard EN 13774.
General Information
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Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Armaturen für Gasverteilungssysteme mit zulässigen Betriebsdrücken kleiner oder gleich als 16 bar - Anforderungen an die GebrauchstauglichkeitAppareils de robinetterie pour les systèmes de distribution du gaz avec une pression maximale de service inférieure ou égale à 16 bar - Exigences de performanceValves for gas distribution systems with maximum operating pressure less than or equal to 16 bar - Performance requirements75.200Petroleum products and natural gas handling equipment23.060.01Ventili na splošnoValves in generalICS:Ta slovenski standard je istoveten z:EN 13774:2013SIST EN 13774:2014en,fr,de01-januar-2014SIST EN 13774:2014SLOVENSKI
STANDARDSIST EN 13774:20031DGRPHãþD
SIST EN 13774:2014
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 13774
February 2013 ICS 23.060.01 Supersedes EN 13774:2003English Version
Valves for gas distribution systems with maximum operating pressure less than or equal to 16 bar - Performance requirements
Appareils de robinetterie pour les systèmes de distribution du gaz avec une pression maximale de service inférieure ou égale à 16 bar - Exigences de performance
Armaturen für Gasverteilungssysteme mit zulässigen Betriebsdrücken kleiner oder gleich 16 bar - Anforderungen an die Gebrauchstauglichkeit This European Standard was approved by CEN on 28 December 2012.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre:
Avenue Marnix 17,
B-1000 Brussels © 2013 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN 13774:2013: ESIST EN 13774:2014
EN 13774:2013 (E) 2 Contents Page Foreword . 4 1 Scope . 5 2 Normative references . 5 3 Terms and definitions . 7 4 Symbols and abbreviations . 8 5 Requirements, type tests and production tests . 8 5.1 Type testing . 8 5.1.1 Test samples . 8 5.1.2 Test documents . 8 5.1.3 Certification body . 9 5.2 Materials . 9 5.2.1 Shell . 9 5.2.2 Obturator . 10 5.2.3 Stem or shaft . 10 5.2.4 Springs . 11 5.2.5 Seals . 11 5.2.6 Lubricants . 11 5.3 Design . 11 5.3.1 General . 11 5.3.2 Strength design . 12 5.3.3 Stems or shafts . 12 5.3.4 Shell tappings . 12 5.3.5 Bolt holes for assembly purposes . 13 5.3.6 Manufacturing apertures. 13 5.3.7 Sealing systems . 13 5.3.8 Extended drain, vent and sealant lines . 13 5.4 Dimensions. 14 5.4.1 Threaded ends. 14 5.4.2 End connections . 15 5.4.3 End-to-end dimensions . 15 5.5 Operability and endurance . 15 5.5.1 Operability . 15 5.5.2 Endurance . 16 5.6 Strength of stops . 16 5.7 Mechanical resistance against excessive actuating forces . 16 5.8 Resistance of the obturator to static differential pressure . 16 5.9 Shell strength . 16 5.10 External leak tightness . 17 5.11 Internal leak tightness . 17 5.12 Resistance to wear (optional test) . 17 5.13 Reference flow rate (optional test) . 18 5.14 Cleanliness . 18 5.15 Storage . 18 6 Marking . 18 Annex A (normative)
Test methods for valves . 20 A.1 Accuracy of measurements and stability . 20 A.2 Test method 1: operability and operating forces test . 20 A.2.1 General . 20 SIST EN 13774:2014
EN 13774:2013 (E) 3 A.2.2 Operability test . 20 A.2.3 Endurance test . 20 A.3 Test method 2: strength of stops . 21 A.3.1 General . 21 A.3.2 Procedure . 21 A.4 Test method 3: resistance of the obturator to static differential pressure . 21 A.5 Test method 4: wear test . 21 A.5.1 General . 21 A.5.2 Procedure . 21 A.6 Test method 5: internal leak tightness test for DIB valves . 22 A.6.1 General . 22 A.6.2 Procedure . 22 A.6.3 Test conditions . 23 A.7 Test method 6: strength test on torque/thrust . 23 A.7.1 General . 23 A.7.2 Measured breakaway torque/thrust . 23 A.7.3 Performance of test . 24 A.7.4 Acceptance criteria . 24 Annex B (informative)
European Standards for valves. 25 Annex C (informative)
Summary of tests on product and type tests . 26 Bibliography . 29
SIST EN 13774:2014
EN 13774:2013 (E) 4 Foreword This document (EN 13774:2013) has been prepared by Technical Committee CEN/TC 69 “Industrial valves”, the secretariat of which is held by AFNOR. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by August 2013, and conflicting national standards shall be withdrawn at the latest by August 2013. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights. This document supersedes EN 13774:2003. This document has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association. The following is a list of the main changes compared to the previous edition: a) the Scope has been modified; b) the Normative References (Clause 2) have been updated; c) requirements of type tests and production tests (Clause 5) have been completely revised, in particular: 1) requirements for “strength design” (5.3.2), for “extended drain, vent and sealant lines” (5.3.8), for “end-to-end dimensions” (5.4.3), for “mechanical resistance against excessive actuating forces” (5.7) have been added; 2) requirements for “resistance to wear” (5.12) and for “reference flow rate” (5.13) became optional; 3) requirements for “bending resistance” and for “resistance to liquid agents” have been deleted; d) the annex on analysis of the technical file and recording of the initial conditions has been deleted; e) the annex on test methods for valves (Annex A) has been updated; f) the annex on additional characteristics on request from the purchaser has been deleted; g) the annex on resistance to bending moment applied via the stem or the shaft has been deleted; h) the annex providing the European Standards for valves (Annex B) has been updated; i) the annex giving a summary of tests on product and type tests (Annex C) has been added; j) the Bibliography has been updated. According to the CEN/CENELEC Internal Regulations, the national standards organisations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom. SIST EN 13774:2014
EN 13774:2013 (E) 5 1 Scope This European Standard deals with metal isolating valves used for gas distribution systems with maximum operating pressure up to 16 bar, and which operate with fuel gases of the first, the second and the third family, in accordance with EN 437. The types of isolating valves to be considered are: plug and ball valves, gate valves, globe valves and butterfly valves. This standard does not apply to: valves for domestic installations; safety type pressure relief valves; wellhead valves. In the case of power operated valves, the requirements for the power source are not covered by this European Standard. The valves covered in this European Standard operate in the following classes of temperature: - 10 °C to 60 °C; - 20 °C to 60 °C; the range is stated by the purchaser for special design. This European Standard gives additional requirements to the relevant products standards. (See Annex B.) In case of contradictions between the standards mentioned in Annex B and this European Standard, EN 13774 prevails. 2 Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 19, Industrial valves — Marking of metallic valves EN 377, Lubricants for applications in appliances and associated controls using combustible gases except those designed for use in industrial processes EN 549, Rubber materials for seals and diaphragms for gas appliances and gas equipment EN 558, Industrial valves — Face-to-face and centre-to-face dimensions of metal valves for use in flanged pipe systems — PN and Class designated valves EN 682, Elastomeric Seals — Materials requirements for seals used in pipes and fittings carrying gas and hydrocarbon fluids EN 736-1:1995, Valves — Terminology — Part 1: Definition of types of valves EN 736-2:1997, Valves — Terminology — Part 2: Definition of components of valves SIST EN 13774:2014
EN 13774:2013 (E) 6 EN 736-3:2008, Valves — Terminology — Part 3: Definition of terms EN 764-1:2004, Pressure equipment — Part 1: Terminology — Pressure, temperature, volume, nominal size EN 1092-1, Flanges and their joints — Circular flanges for pipes, valves, fittings and accessories, PN designated — Part 1: Steel flanges EN 1092-2, Flanges and their joints — Circular flanges for pipes, valves, fittings and accessories, PN designated — Part 2: Cast iron flanges EN 1092-3, Flanges and their joints — Circular flanges for pipes, valves, fittings and accessories, PN designated — Part 3: Copper alloy flanges EN 1555-1, Plastics piping systems for the supply of gaseous fuels — Polyethylene (PE) — Part 1: General EN 1555-2, Plastics piping systems for the supply of gaseous fuels — Polyethylene (PE) — Part 2: Pipes EN 1555-3, Plastics piping systems for the supply of gaseous fuels — Polyethylene (PE) — Part 3: Fittings EN 1759-1, Flanges and their joint — Circular flanges for pipes, valves, fittings and accessories, Class designated — Part 1: Steel flanges, NPS 1/2 to 24 EN 1759-3, Flanges and their joints — Circular flanges for pipes, valves, fittings and accessories, Class designated — Part 3: Copper alloy flanges EN 10204, Metallic products — Types of inspection documents EN 10226-1, Pipe threads where pressure tight joints are made on the threads — Part 1: Taper external threads and parallel internal threads — Dimensions, tolerances and designation EN 12117, Plastics piping systems — Fittings, valves and ancillaries — Determination of gaseous flow rate/pressure drop relationships EN 12266-1:2012, Industrial valves — Testing of metallic valves — Part 1: Pressure tests, test procedures and acceptance criteria — Mandatory requirements EN 12516-1, Industrial valves — Shell design strength — Part 1: Tabulation method for steel valve shells EN 12516-2, Industrial valves — Shell design strength — Part 2: Calculation method for steel valve shells EN 12516-3, Valves — Shell design strength — Part 3: Experimental method EN 12516-4, Industrial valves — Shell design strength — Part 4: Calculation method for valve shells manufactured in metallic materials other than steel EN 12570, Industrial valves — Method for sizing the operating element EN 12627, Industrial valves — Butt welding ends for steel valves EN 12982, Industrial valves — End-to-end and centre-to-end dimensions for butt welding end valves EN 13942, Petroleum and natural gas industries — Pipeline transportation systems — Pipeline valves (ISO 14313:2007 modified) EN ISO 228-1, Pipe threads where pressure-tight joints are not made on the threads — Part 1: Dimensions, tolerances and designation (ISO 228-1) SIST EN 13774:2014
EN 13774:2013 (E) 7 EN ISO 8434-1, Metallic tube connections for fluid power and general use — Part 1: 24 degree cone connectors (ISO 8434-1) ISO 272, Fasteners — Hexagon products — Widths across flats ASME B1.20.1, Pipe Threads, General Purpose (Inch) 3 Terms and definitions For the purposes of this document, the terms and definitions given in EN 736-1:1995, EN 736-2:1997,
EN 736-3:2008 and EN 764-1:2004 and the following apply. 3.1 gas distribution system pipeline system including piping above and below ground and all other equipment necessary to supply the gas to the consumers 3.2 external tightness
shell tightness tightness of the gas-containing envelope with respect to the atmosphere 3.3 internal tightness seat tightness tightness ensured between the valve inlet and outlet by the closure device in the closed position 3.4 volume rate of flow volume of fluid discharged by the valve per time unit 3.5 reference flow rate rate of the air flow in cubic metres per hour, as measured at 0 °C at the absolute pressure of 1 013 mbar, discharged by the valve and creating therein a specified pressure drop, at a specified air pressure upstream of the valve 3.6 maximum allowable pressure pmax maximum pressure at which any part of a valve continuously operates at a specified operating temperature 3.7 maximum operating pressure MOP maximum pressure in a system operated continuously under normal operating conditions Note 1 to entry: "Normal operating conditions" means no malfunctioning of the equipment or disruption to the gas flow. 3.8 maximum strength torque maximum torque applied to the stem or the shaft, with the obturator either totally open or totally closed, which causes no alteration to the functional capability of the valve SIST EN 13774:2014
EN 13774:2013 (E) 8 3.9 maximum operating torque maximum torque applied on the stem or shaft of a valve to ensure its operation under the maximal allowable pressure (pmax) and at any operating temperature 3.10 operating cycle full operating from the closed position to the opened position and back to the closed position 3.11 block and bleed facility equipment put together with the valve as to assume two functions: isolation and bleed 3.12 double-isolation-and-bleed valve
DIB single valve with two seating surfaces, each of which, in the closed position, provides a seal against pressure from a single source, with a means of venting/bleeding the cavity between the seating surfaces Note 1 to entry: This feature can be provided in one direction or in both directions. 4 Symbols and abbreviations ta : mean ambient temperature (+ 20 °C ± 5 °C); tmax : maximum value of use temperature (+ 60 °C); tmin : minimum value of use temperature; pmax : maximum allowable pressure. 5 Requirements, type tests and production tests 5.1 Type testing 5.1.1 Test samples Qualification of the range shall be achieved by testing the smallest valve, the largest valve limited by DN 500 and one chosen in the middle of the range. For valves greater than DN 500, the DN 500 qualifies the range up to DN 1 000. This applies only where the materials, design and construction does not change within the range. For resistance to wear, qualification shall be achieved by testing only the smallest of the range. For each valve to be tested, one sample should be provided, and tested in accordance with the qualification test program. 5.1.2 Test documents The manufacturer shall produce a technical file containing the following documents: a) detailed drawings, including dimensions, tolerances, surface conditions and relevant calculations for pressure containing parts and principle parts; b) detailed drawings of the isolating valve with sectional drawings of all important parts; SIST EN 13774:2014
EN 13774:2013 (E) 9 c) general arrangement drawings showing relative positions and sizes of vents/drains, gearboxes, and other external parts, together with overall dimensions; d) manufacturing details including welding and testing procedures; e) installation, operating and maintenance procedures; f) description of the isolating valve with details on type, construction, materials, surface treatment and marking; detailed sectional arrangement drawings showing all parts with reference numbers and materials identified to published standards including reference to the elastomers and to the suppliers; g) details of technical characteristics including performance details. The manufacturer shall state the reference flow rate at full opening; h) material certificates in accordance with EN 10204 shall be supplied with the samples: 1) Type 3.1 for the body and obturator, 2) Type 2.2 for the stem or shaft. 5.1.3 Certification body All tests shall be certified by an independent accepted body. 5.2 Materials 5.2.1 Shell Requirements Type tests Production tests 5.2.1.1 General Materials in accordance with EN 12516-1, EN 12516-2 or EN 12516-4 shall be used, except grey cast iron, taking into account the relevant standards for shell design strength. Other metallic materials may only be used if their mechanical characteristics, temperature stability and resistance to corrosion are at least equal to those specified in the above cited standards.
The technical data concerning the materials used shall be available from the valve manufacturer.
_ 5.2.1.2 Steel weldings ends For welding ends of valves, the maximum carbon equivalent CEVmax shall not exceed: CEVmax = 0,45 for grades with specified minimum yield strength not exceeding 360 N/mm2; CEVmax = 0,48 for grades with specified minimum yield strength above 360 N/mm2; unless otherwise agreed between purchaser and manufacturer. 5%%%6%%maxVMoCrMnCCEV++++=
SIST EN 13774:2014
EN 13774:2013 (E) 10 Requirements Type tests Production tests 15%%NiCu++ where
% is the percentage by weight of the ladle content of: C Carbon; Mn Manganese; Cr Chromium; Mo Molybdenum; V Vanadium; Cu Copper; Ni Nickel. Unless otherwise agreed between manufacturer and purchaser, the carbon content shall not exceed 0,21 %. The sulphur content shall not exceed 0,030 %, and the phosphorus content shall not exceed 0,035 %. The sum of sulphur and phosphorus as a total of the ladle analysis shall be smaller than or equal to 0,050 %. 5.2.1.3 PE ends Materials in accordance with EN 1555-1 shall be used.
5.2.2 Obturator Requirements Type tests Production tests Materials in accordance with EN 12516-1, EN 12516-2 or EN 12516-4 shall be used. The technical data concerning the materials used shall be available from the valve manufacturer. _ 5.2.3 Stem or shaft Requirements Type tests Production tests Stem or shaft shall be made from metallic materials and shall be corrosion resistant or permanently protected against corrosion. The technical data concerning the materials used shall be available from the valve manufacturer. _
SIST EN 13774:2014
EN 13774:2013 (E) 11 5.2.4 Springs Requirements Type tests Production tests Springs necessary for operation and leak tightness shall be made of corrosion resistant materials or their permanent resistance to corrosion shall be made by means of design. Protection of the surface is not permissible. The technical data concerning the materials used shall be available from the valve manufacturer. _ 5.2.5 Seals Requirements Type tests Production tests Seals made of elastomers shall meet the requirements of EN 682 or EN 549. When seals made of thermo plastic materials, e.g. PTFE, PA are used, the part in contact with the flow shall be of non-regenerated material. When seals made of thermoplastic materials are used, the sealing system shall be designed in such a way to compensate a possible creep of the seal. Reinforcement with carbon or fibreglass is allowed. The technical data concerning the materials used shall be available from the valve manufacturer. _ 5.2.6 Lubricants Requirements Type tests Production tests Lubricants used in gas containing parts shall meet the specifications of EN 377. The technical data concerning the materials used shall be available from the valve manufacturer. _ 5.3 Design 5.3.1 General Requirements Type tests Production tests Isolating valves shall be free from sharp edges. A visual inspection shall be carried out to verify conformance to the requirements. The requirement is to be verified through a visual inspection of each valve. SIST EN 13774:2014
EN 13774:2013 (E) 12 5.3.2 Strength design Requirements Type tests Production tests The design and dimensions of the valves shall be such as to withstand safely all stresses occurring under operating conditions. The shell design shall meet the requirements of EN 12516-1 or EN 12516-2 or EN 12516-3 or EN 12516-4. Alternatively, by agreement, the requirements of EN 13942 shall be met. NOTE The tabulation method, EN 12516-1, is similar in approach to ASME B16.34 in that the designer can look up the required minimum wall thickness dimension of the valve body from a table. The calculations or the elevated pressure test report shall be included in the technical file the manufacturer shall produce. See 5.1.2. – 5.3.3 Stems or shafts Requirements Type tests Production tests Stems or shafts shall be of anti-blow out design. The stem seal fasteners shall not be considered as being the sole anti-blow out method. The stem shall be protected against water and dust ingress. A visual inspection shall be carried out to verify conformance to the requirements. The requirement is to be checked through
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