SIST EN 13959:2005

Anti-pollution check valves - DN 6 to DN 250 inclusive family E, type A, B, C and D

The purpose of this European Standard is to specify:
-   field of application of Anti-pollution Check Valves;
-   backflow prevention properties, dimensional and physio-chemical properties, and properties of general hydraulic, mechanical and acoustic design to which Anti-pollution Check Valves of nominal sizes DN 6 to DN 250 inclusive shall conform;
-   Family E, type A, controllable Anti-pollution Check Valve (with test port);
-   Family E, type B, non-controllable Anti-pollution Check Valve, including Cartridge Check Valve;
-   Family E, type C, controllable Anti-pollution Double Check Valve (with test ports);
-   Family E, type D, non-controllable Anti-pollution Double Check Valve, including Cartridge Double Check Valve;
-   test procedures and requirements for verifying the backflow protection properties of stop valves, draw-off taps etc. which incorporate a check valve function. Stop valves, draw off taps etc, need also to comply with a recognised standard;
-   marking;
-   presentation at delivery.
This standard specifies the characteristics of Anti-pollution Check Valves of DN 6 up to and including DN 250 that are suitable for use in drinking water systems. For application feasibility see Table 1.
Table 1 - Nominal size vs Conditions of use
Nominalsize(DN)   Max. Operatingtemperature   Max. Operating pressure   Installation
DN <= 50                   65 °C + 90 °C, 1 hour   1 000 kPa (10 bar)                   Any position
DN > 50                   65 °C                                   1 000 kPa (10 bar)                   Horizontal only
Anti-pollution Check Valves covered by this standard are of Pressure Class PN 10.
The field of application of EN 1717 is limited to 10 bar, flanges could be drilled in PN 16 pattern.
Anti-pollution Check Valves of PN 16 shall satisfy the requirements of standard EN 13959 and comply with tests which characterise the PN of the device.

Rückflussverhinderer - DN 6 bis DN 250 - Familie E, Typ A, B, C und D

Clapets de non-retour antipollution - DN 6 a DN 250 inclus - Famille E, Type A, B, C et D

Protipovratni ventili za preprečevanje onesnaževanja – DN 6 do DN 250, vključno z družino E, vrste A, B, C in D

General Information

• Status: Published
• Publication Date: 28-Feb-2005
• ICS: 23.060.50 - Check valves
• Technical Committee: IOVO - Water supply and waste water engineering
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Mar-2005
• Due Date: 01-Mar-2005
• Completion Date: 01-Mar-2005
• Directive: 89/106/EEC - Construction products
• Mandate: M/EXP - Expected mandates in CPD field.
• Ref Project: EN 13959:2004 - Anti-pollution check valves - DN 6 to DN 250 inclusive family E, type A, B, C and D

Standards Content (Sample)

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Rückflussverhinderer - DN 6 bis DN 250 - Familie E, Typ A, B, C und DClapets de non-retour antipollution - DN 6 a DN 250 inclus - Famille E, Type A, B, C et DAnti-pollution check valves - DN 6 to DN 250 inclusive family E, type A, B, C and D23.060.50Blokirni ventiliCheck valvesICS:Ta slovenski standard je istoveten z:EN 13959:2004SIST EN 13959:2005en01-marec-2005SIST EN 13959:2005SLOVENSKI
STANDARD



SIST EN 13959:2005



EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 13959October 2004ICS 23.060.50 English versionAnti-pollution check valves - DN 6 to DN 250 inclusive family E,type A, B, C and DClapets de non retour antipollution DN 6 à DN 250 - FamilleE, Type A, B, C et DRückflussverhinderer - DN 6 bis DN 250 - Familie E, Typ A,B, C und DThis European Standard was approved by CEN on 22 July 2004.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the Central Secretariat or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the officialversions.CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2004 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 13959:2004: ESIST EN 13959:2005



EN 13959:2004 (E) 2 Contents page Foreword.3 Introduction.4 1 Scope.5 2 Normative references.6 3 Terms and definitions.7 3.1 Anti-pollution check valves.7 3.2 Flanged anti-pollution check valves; class a and class b.7 3.3 Combined product.8 4 Nominal size.8 5 Designation.8 6 Marking and technical documents.9 6.1 Marking.9 6.2 Technical documents.9 7 Symbolization.10 8 General design characteristics.10 8.1 Overall length and diameters of check valves.10 8.2 End connections.12 8.3 Test and drain ports.12 8.4 Other characteristics.13 9 Physio-chemical characteristics.14 9.1 Materials.14 9.2 Nature of materials.14 10 Test Arrangements.15 10.1 Sequence of testing.15 10.2 Apparatus.16 11 Hydraulic and mechanical characteristics.17 11.1 High velocity (stage 1).17 11.2 Flow rate/pressure loss (stage 2).18 11.3 Mechanical strength of the body (stage 3).19 11.4 Bending moment (stage 4).20 11.5 Pressure tightness under a low reverse pressure differential (stage 5).22 11.6 Pressure tightness under a high reverse pressure and verification that the check valve
has not jammed (stage 6).24 11.7 Pressure differential at which the check valve closes (stage 7).25 11.8 Compatibility with products used for disinfection of networks (stage 8).25 11.9 Endurance (stage 9).26 11.10 Pressure tightness under a low reverse pressure differential (stage 10).28 11.11 Pressure tightness under a high reverse pressure and verification that the check valve
has not jammed (stage 11).28 11.12 Pressure differential at which the check valve closes (stage 12).28 12 General working characteristics.29 12.1 Resistance to corrosion.29 12.2 Acoustic characteristics.29 13 Presentation at delivery.30 Annex A (informative)
Numbers of test devices/tests.31
SIST EN 13959:2005



EN 13959:2004 (E) 3 Foreword This document (EN 13959:2004) has been prepared by Technical Committee CEN/TC 164 “Water supply”, 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 April 2005, and conflicting national standards shall be withdrawn at the latest by April 2005. This standard has been worked out in reference EN 1717, Protection against pollution of potable water in wa-ter installations and general requirements of devices to prevent pollution by backflow. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic, Den-mark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxem-bourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. SIST EN 13959:2005



EN 13959:2004 (E) 4 Introduction In respect of potential adverse effects on the quality of water intended for human consumption, caused by the product covered by this document: a) this document provides no information as to whether the product may be used without restriction in any of the Member States of the EU or EFTA; b) it should be noted that, while the adoption of verifiable European criteria, existing national regulations concerning the use and/or the characteristics of this product remain in force. SIST EN 13959:2005



EN 13959:2004 (E) 5 1 Scope The purpose of this document is to specify:  field of application of anti-pollution check valves;  backflow prevention properties, dimensional and physio-chemical properties, and properties of general hydraulic, mechanical and acoustic design for anti-pollution check valves of nominal sizes DN 6 to DN 250 inclusive;  family E, type A, controllable anti-pollution check valve (with test port);  family E, type B, non-controllable anti-pollution check valve, including cartridge check valve;  family E, type C, controllable anti-pollution double check valve (with test ports);  family E, type D, non-controllable anti-pollution double check valve, including cartridge double check valve;  test procedures and requirements for verifying the backflow protection properties of stop valves, draw-off taps etc. which incorporate a check valve function. Stop valves, draw off taps etc, need also to comply with a recognised standard;  marking;  presentation at delivery. This document specifies the characteristics of anti-pollution check valves of DN 6 up to and including DN 250 that are suitable for use in drinking water systems. For application feasibility see Table 1. Table 1 — Nominal size vs Conditions of use Nominal size (DN) Max. Operating temperature Max. Operating pressure Installation DN ≤ 50 65 °C + 90 °C, 1 h 1 000 kPa (10 bar) Any position DN > 50 65 °C 1 000 kPa (10 bar) Horizontal only
Anti-pollution check valves covered by this document are of pressure class PN 10. In case of devises with pres-sure class PN 16, the anti–pollution check valves has to comply with the tests which characterise the PN of the devise. The field of application of EN 1717 is limited to 10 bar, flanges could be drilled in PN 16 pattern. SIST EN 13959:2005



EN 13959:2004 (E) 6 2 Normative references The following referenced documents are indispensable for the application of this document. For dated refer-ences, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 558-1, Industrial valves — Face-to-face and centre-to-face dimensions of metal valves for use in flanges pipe systems — Part 1: PN-designated valves. EN 1092-1, Flanges and their joints — Circular flanges for pipes, valves, fittings and accessories, PN desig-nated — Part 1: Steel flanges. EN 1092-2, Flanges and their joints — Circular flanges for pipes, valves, fittings and accessories, PN desig-nated — Part 2: Cast iron flanges. EN 1092-3, Flanges and their joints — Circular flanges for pipes, valves, fittings and accessories, PN desig-nated — Part 3: Copper alloy flanges. EN 1254-1, Copper and copper alloys — Plumbing fittings — Part 1: Fittings with ends for capillary soldering or capillary brazing to copper tubes. EN 1254-2, Copper and copper alloys — Plumbing fittings — Part 2: Fittings with compression ends for use with copper tubes. EN 1254-3, Copper and copper alloys — Plumbing fittings — Part 3: Fittings with compression ends for use with plastics pipes. EN 1254-4, Copper and copper alloys — Plumbing fittings — Part 4: Fittings combining other end connections with capillary or compression ends. EN 1267, Valves - Test of flow resistance using water as test fluid. EN 1717, Protection against pollution of potable water in water installations and general requirements of de-vices to prevent pollution by backflow. EN ISO 3822-1, Acoustics — Laboratory tests on noise emission from appliances and equipment used in water supply installations — Part 1: Method of measurement (ISO 3822-1:1999). EN ISO 3822-3, Acoustics — Laboratory tests on noise emission from appliances and equipment used in water supply installations — Part 3: Mounting and operating conditions for in-live valves and appliances (ISO 3822-3:1997).
EN ISO 5167-3, Measurement of fluid flow by means of pressure differential devices inserted in circular cross-section conduits running full — Part 3: Nozzles and Venturi nozzles (ISO 5167-3:2003). EN ISO 6509, Corrosion of metals and alloys — Determination of dezincification resistance of brass (ISO 6509:1981). ISO 9227, Corrosion tests in artificial atmospheres — Salt spray tests. SIST EN 13959:2005



EN 13959:2004 (E) 7 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 Anti-pollution check valves [ul5]3.1.1
family E, type A, controllable anti-pollution check valve (with test port) controllable single check valve, consisting one closing element, is mechanical protection device to permit flow in one direction only. It will open automatically when the pressure in the direction of flow upstream of the valve is greater than the pressure downstream. In case when the pressure is higher downstream or no flow condi-tion exists the valve is closed by anticipation acting under a force, for example of a mechanical assembly or a spring. For verification needs this type of check valve has a test cock upstream of the closing element 3.1.2
family E, type B, non-controllable anti-pollution check valve non-controllable single check valve, consisting one closing element, is a mechanical protection device to per-mit flow in one direction only. It will open automatically when the pressure in the direction of flow upstream of the valve is greater than the pressure downstream. In case when the pressure is higher downstream or no flow condition exists the valve is closed by anticipation acting under a force, for example of a mechanical as-sembly or a spring. A family E, type B, non-controllable anti-pollution check valve is constructed in two formats:  With housing (final product);  Without housing (called cartridge check valve) 3.1.3
family E, type C, controllable double anti-pollution check valve (with test ports) controllable double check valve, consisting of two independent acting closing elements, is a mechanical protection device to permit flow in one direction only. It will open automatically when the pressure in the direction of flow upstream of the valve is greater than the pressure downstream. In case when the pressure is higher downstream or no flow condition exists the valve is closed by anticipation acting under a force, for example of a mechanical assembly or a spring. For verification needs this type of check valve has a test cock upstream of each closing element 3.1.4
family E, type D, non-controllable anti-pollution double check valve non-controllable double check valve, consisting two independent acting closing elements, is a mechanical pro-tection device to permit flow in one direction only. It will open automatically when the pressure in the direction of flow upstream of the valve is greater than the pressure downstream. In case when the pressure is higher downstream or no flow condition exists the valve is closed by anticipation acting under a force, for example of a mechanical assembly or a spring. A family E, type D, non-controllable anti-pollution double check valve is constructed in two formats:  With housing (final product);  Without housing (called cartridge double check valve) For the purpose of this document, "anti-pollution check valves" are hereafter referred to as "devices" 3.2
flanged anti-pollution check valves; class a and class b controllable check valves need to be accessible for inspection, test and replacement. To assist their repair, flanged check valves may be provided with an inspection hatch and for designation pur-poses two classes are specified:  Class a : with an inspection hatch; SIST EN 13959:2005



EN 13959:2004 (E) 8  Class b : without an inspection hatch; The installation of either a class a device or a class b device depends on national installation requirements 3.3
combined product a combined product is an end product which incorporates beside the check valve function other function(s)
EXAMPLES stop valves, draw-off taps etc. which incorporate a check valve function 4 Nominal size For the purpose of this document the nominal size DN as given in Table 6 relates to flow characteristics. The dimensions of the end connections shall be either equal to or one DN smaller, or one DN greater than the nominal size of the device, except for the flanged devices of which the connecting size shall correspond to DN. The DN-range covered by this document for single check valves (type A and B) and double check valves (type C and D) is DN 6 to DN 250 inclusive. Limitations are given in the applicable tables. 5 Designation Devices are designated by:  its name;  its family (E);  its type (A, B, C and D);  its class (a or b for flanged devices only, see 3.2 and 8.4.2.1);  its nominal size (DN) (see Table 6);  its pressure class (PN);  its connections: type and size (not applicable to cartridge check valves);  its housing material (not applicable to cartridge check valves);  its surface finish (possible coating);  the acoustic group (up to DN 32 inclusive only);  reference to this document. Examples of designation Non-controllable anti-pollution check valve, family E, type B, DN 20, G ¾ × G ¾, bronze, I, EN 13959. Controllable anti-pollution check valve, family E, type A, class a, DN 100, Flanged, Pressure class 10, Epoxy coated ductile iron, EN 13959. SIST EN 13959:2005



EN 13959:2004 (E) 9 6 Marking and technical documents 6.1 Marking Devices shall be marked permanently and visibly on housings, or on a fixed identification plate. In the case of car-tridge check valves marking shall be on the cartridge itself. This information shall be on the upper side, or on each lateral side of the device. The indications are to be inde-lible and obtained by moulding, engraving or similar procedures. The marking shall indicate: a) name, manufacturer's brand or logo; b) arrow indicating normal direction of flow; c) letter indicating family and type of the device; d) nominal size (DN); e) nominal pressure (PN); f) maximum operating temperature in degrees Celsius (°C); g) acoustic group (up to DN 32 inclusive only); h) manufacturer’s reference; i) reference to the present standard; j) dezincification resistance. In the countries where the use of products made of dezincification resistant materials is not required, the dezincification resistant products according to EN ISO 6509 as well as the products, which do not contain zinc, are allowed to be marked << DR >>. In countries where the use of dezincification resistant materials is required, the dezincification resistant products as well as the products, which do not contain zinc, shall be marked <>. For all devices marking a), b), c) and d) are obligatory. For flanged devices e) is also obligatory. In case there is no marking for g), the device has to be considered as not classified acoustically. Where space permits the other information shall be marked in the following order: f) to j). Cartridge check valve shall be marked with a), b) and d). Other markings are optional. 6.2 Technical documents Each package and/or each batch and/or each catalogue of the supplier/manufacturer should contain Techni-cal Product Information (TPI) which shall be written in a commonly spoken language of the country in which the product is sold. If the TPI is not supplied it shall be available on request. TPI shall provide the following information:  designation and purpose of the product; SIST EN 13959:2005



EN 13959:2004 (E) 10  installation instructions;  (brand) name and address of supplier / manufacturer;  instructions for maintenance, if any;  spare part list, if any;  nature of materials. 7 Symbolization The graphic representation of the device is as follows (see Figures 1 and 2):
EA with test port
EB without test port NOTE Applies also for cartridge check valves. Figure 1 — Check valve symbols
EC with test port
ED without test port NOTE Applies also for Cartridge Double Check Valves. Figure 2 — Double check valve symbols 8 General design characteristics 8.1 Overall length and diameters of check valves 8.1.1 General Where necessary, the overall lengths and diameters of check valves are specified for each type in 8.1.2 to 8.1.5. 8.1.2 Check valves with threaded ends or compression ends The overall lengths of check valve housings with threaded ends or compression ends or with ends suitable for connection with capillary unions shall be determined by the manufacturer. SIST EN 13959:2005



EN 13959:2004 (E) 11 8.1.3 Flanged check valves The overall length of flanged check valves EA shall be in accordance with EN 558-1 (series f1 and f48) and is given in Table 2. Table 2 — Nominal size vs overall length (face to face) of flanged check valves Nominal size (DN) 40 50 65 80 100 125 150 200 250 Short (f48) 180 200 240 260 300 350 400 500 600 Length (mm) Long (f1) 200 230 290 310 350 400 480 600 730
Alternative face-to-face dimensions within the scope of EN 558-1 are permissible by agreement with the customers. 8.1.4 Cartridge check valves The cartridge check valves mounting dimensions for retention and leak tightness shall be determined and provided by the cartridge supplier, with the exception of one kind of water meter cartridge check valves (see Figure 3), having dimensions given in Table 3.
Figure 3 — Water meter cartridge check valve Table 3 — Dimensions of water meter cartridge check valves Dimensions in millimetres DN 15 20 25 40 D1 (max) 18,3 22,1 28,5 40,3 L (max) 19,5 25,5 38,5 50,0
D2
0 20,0 -0,15
0 25,0 –0,15
0 32,0 –0,2
0 46,0 –0,3 h 3,0 ± 0,1 7,0 ± 0,1 8,0 ± 0,1 10,0 ± 0,1
8.1.5 Double Check Valves The overall length of this type of check valve is left to the discretion of the manufacturer. SIST EN 13959:2005



EN 13959:2004 (E) 12 8.2 End connections 8.2.1 General End connections for check valves are specified for each type in 8.2.2 to 8.2.4. 8.2.2 Threaded end connections Threaded end connections shall comply with EN 1254, parts 1, 2, 3 and 4. End connections shall be designed so that when a pipe or fitting is connected to the threaded portion of the check valve body it shall not adversely affect the operation of the valve. Direct soldering or brazing of piping to check valve is not permitted. Any such connections shall be by means of unions with nuts and capillary tailpieces. 8.2.3 Flanged end connections Flanged end connections shall comply with EN 1092, parts 1, 2 and 3. Other requirements to end connections of flanged check valves: a) the inlet and outlet flanges shall be of the same size; and b) the flanges shall be of the same DN as the device. 8.2.4 Other connections Other end connections are not precluded providing: a) they comply with current national standards; b) the device complies with all other requirements of this standard. 8.3 Test and drain ports EA and EC check valve bodies shall include:  a test port fitted with a plug on the inlet side (EA and EC) and a test port with a plug in the intermediate chamber (EC), so as to permit the leak-tightness of the check valve(s) to be verified in-situ.  for flanged check valves a quarter-turn test cock fitted to the test port. Check valve bodies may also include:  a drain port with a plug on the outlet side, to facilitate downstream draining in-situ. Internal parts shall not obstruct the test and drain ports. Controllable check valves shall have test port(s) and optional drain ports according to the specification as shown in Figure 4 and Table 4. The bores of test and drain ports shall have over their full length a minimum cross-section of 12,56 mm2. Their smallest dimension shall be 4 mm. SIST EN 13959:2005



EN 13959:2004 (E) 13
Figure 4 — Test and drain ports Table 4 — Dimensions of test and drain ports Nominal size DN Thread size a a (mm) ≤15 G é or G ¼ > 6,5 15 < DN ≤ 50 G ¼ > 6,5 > 50 G ê or G ½ > 13 a Thread shall be in accordance with EN 1254-4.
The test and drain ports shall be produced so that the plug can be adequately sealed. 8.4 Other characteristics 8.4.1 Double check valves The components of the two check valves shall not interfere with each other in all operating conditions. 8.4.2 Flanged check valves 8.4.2.1 Accessibility When installed, controllable check valves shall be accessible for inspection, test and replacement. To assist their repair, flanged check valves may be provided with an inspection hatch and for designation pur-poses, 2 classes are specified:  Class a : with an inspection hatch;  Class b : without an inspection hatch. Inspection hatches shall be adequately sized to permit maintenance. The installation of either a class a device or a class b device depends on national installation requirements. 8.4.2.2 Flanged check valves with inspection hatch Class a devices which retain water with the inspection hatch removed shall be fitted with a drain port at the bottom of the chamber. SIST EN 13959:2005



EN 13959:2004 (E) 14 8.4.3 Replaceable components Replaceable components to be used on site shall be in the form of a sub-assembly and be designed so that they can only be re-assembled in the check valve housing without error in the correct positions (with no risk of insertion reversal etc). Cartridge check valves are excluded from this requirement. These devices shall be replaced entirely. They are considered to be sub-assemblies. 9 Physio-chemical characteristics 9.1 Materials The materials and the coatings used, liable to come normally or accidentally in contact with potable water, shall satisfy the EC regulations concerning water quality. And therefore they:  shall be corrosion resistant in accordance with ISO 9227;  shall be prone to the least scaling possible;  shall be in conformity with the European Standards and regulations;  shall be compatible among themselves and  with the water distributed;  with the fluids or matter liable to come into contact with them;  with the products normally used for disinfection of installations; potassium permanganate and sodium hypochlorite. 9.2 Nature of materials a) The choice of materials is left to the discretion of the manufacturer.
NOTE This standard does not cover non-metallic housings. Copper-zinc alloys containing more than 10 % zinc are subject to dezincification when submitted to water capable to dezincification. In countries where the use of products made of dezincification resistant mate-rials is required, the products have to guarantee a dezincification depth less than 200 µm in any direction, they have to be tested in accordance with standard EN ISO 6509 and have to be marked in compliance with the indications under section ”Marking” (see 6.1 of this document). b) Neither the materials nor coatings used shall, by normal or accidental contact with drinking water, cause any risk of affecting or modifying the water up to a temperature of 90 °C. The suitability of the water for human consumption is defined by national regulations. c) The manufacturer shall state in his technical and sales literature the nature of the materials and the coat-ings selected. d) The materials, and in particular copper alloys, for which recommendations or international standards exist, shall comply with the relevant recommendations or international standards. SIST EN 13959:2005



EN 13959:2004 (E) 15 10 Test Arrangements 10.1 Sequence of testing The test device shall be tested in a position so that the inlet/outlet and obturator axis is in one horizontal plane. The test sequences on samples is suggested in Annex A. The hydraulical and mechanical testing sequence is as follows: Stage 1 High velocity test. See 11.1 Stage 2 Flow rate and pressure loss test. See 11.2 Stage 3 Mechanical strength of body. See 11.3 Stage 4 Bending moment test (incl. 1,6 MPa body pressure and 3 cmwc reverse pressure). See 11.4 Stage 5 Pressure tightness under a low reverse pressure differential (3 cmwc reverse pressure). See 11.5 Stage 6 Pressure tightness under a high reverse
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