General Technical Approval

DIBt 

General 

Technical 

Approval 

German Institute for Construction 

Engineering 

PUBLIC-LAW INSTITUTION 

Approval body for construction products and types 

of construction 

German Construction Industry Inspection Authority 

Member of the European Organisation for Technical Approvals 

EOTA and of the Member of the European Association for 

Technical Approval in Construction UEAtc 

Phone: +49 30 78730-0 

Fax: +49 30 78730-320 

E-Mail: dibt@dibt.de 

Date: 

Reference 

27 July 2009 I 54-1.65.25-63/08 

Approval number: 

Duration of validity until: 

Z-65.25-220 30 June 2014 

Applicant: 

Klenk GmbH 

Eichelstraße 15, D-88285 Bodnegg-Rotheidlen 

Object of approval: 

Flexible double-walled pipe for transport of water-hazardous liquids during 

transfer and filling procedures (system conceived and made by the company 

Klenk) 

The Construction Inspection Industry Authority hereby approves the above-specified product. 

This General Technical Approval comprises eight pages, including five Annexes (five additional 

pages). It replaces the General Technical Approval certificate No. Z-65.25-220 dated 8 June 

1999 issued by the Construction Inspection, which had last been extended on July 20, 2004. 

German Institute for Construction and Engineering | An Institution of the German Federation and of the Federal States 

DIBt | Kolonnenstraße 30 L | D-10829 Berlin | Phone: +4930 78730-0 | Fax: +4930 78730-320 | E-Mail: dibt@dibt.de j www.dibt.de

DIBt 

General Technical Approval Page 2 of 8 | 27 July 2009 

Z-65.25-220 

I. GENERAL PROVISIONS 

1 This General Technical Approval provides evidence that the approved product is suited for application and 

use within the meaning of the building and construction regulations enacted by the different Federal States. 

2 This General Technical Approval does not replace the permits, licences and certifications otherwise required 

by the German law for the execution of building and/or construction projects. 

3 This General Technical Approval is granted without prejudice to the rights, particularly private property rights, 

of any third parties. 

4 The manufacturer and distributor of the approved product must, without prejudice to more extensive 

regulations contained in the SPECIAL PROVISIONS stated below, provide the user of the approved product 

with copies of the General Technical Approval by pointing to the fact that the General Technical Approval has 

to be available at the place where the approved object or system is used. On request, the involved authorities 

are, likewise, to be provided with copies of the General Technical Approval. 

5 The General Technical Approval many be reproduced only in whole. The publication of the Approval in 

excerpts is subject to the German Construction Industry Inspection Authority's prior consent (Deutsches 

Institut für Bautechnik, DIBt). Texts and drawings publicized in promotional literature must not be contrary to 

the specifications laid down in this General Technical Approval. All translations of the General Technical 

Approval must contain the hint phrase "Translation of the original German version not reviewed by the 

German Construction Industry Inspection Authority (DIBt)". 

6 The General Technical Approval is granted subject to revocation at any time. The terms of the General 

Technical Approval can subsequently be altered and/or amended, particularly if new technical knowledge 

requires doing so.

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Z-65.25-220 

II. SPECIAL PROVISIONS 

1 Object of approval and scope of application 

(1) This General Technical Approval concerns and relates to flexible double-walled (jacketed) hose 

lines with leak detection, a system conceived and made by the company Klenk, bearing the type 

designation DWSL and comprising an associated intermediate layer serving as a spacer element and a 

hose connection fitting consisting of connection fittings, nipples and sleeves or hose connecting pieces 

existing on the hose side, including connection parts, such as clamps, hose screw connections or 

flanges or tanker couplings and the material needed for sealing them. The flexible pipes are 

manufactured including inner hoses in sizes from DN 15 up to DN 75 and lengths of up to 50m. They 

are suited for connection to a vacuum leak detector that allows to detect negative pressures of up to 

-550mbar and alarm vacuum levels of at least -325mbar (as for the design of the flexible double-walled 

pipe, please refer to Annex 1 hereto). 

(2) The leak detector reacts and warns optically and acoustically if, in consequence of leaks in the 

walls of the flexible double-walled pipe, the pressure level in the monitored space rises. 

(3) The flexible double-walled pipes are admitted for the conveying of water-hazardous liquids during 

transfer and/or filling operations at pumping pressures of up to 10bar. 

(4) The flexible double-walled pipes are admitted for use within a temperature range from -20°C up to 

+60°C on condition that evidence is furnished with regard to their suitability in regard to all materials 

and liquids that, during the transfer of the related water-hazardous liquid, could get in touch with each 

other in a certain section of the admissible overall temperature range. 

(5) The General Technical Approval is hereby granted without prejudice to the provisos on testing or 

other law sectors, such as the Directive 97/23/EC (Pressure Equipment Directive), the eleventh 

regulation on the device safety law (regulation on placing devices and safety systems in circulation for 

hazardous areas - explosion protection regulation and the ordinances on § 18 of the German 

Occupational Safety and Health Act, the German Ordinance on Industrial Safety and Health and the 

German Ordinance on Hazardous Substances). 

(6) Owing to this General Technical Approval, the assessment in regard to the approved product's 

compliance with the regulations of the Federal Water Act, including the type-approval procedure 

required by the German Water Management Law (§ 19 h WHG 1 ) are inapplicable. 

(7) The validity period of this General Technical Approval (see page 1) relates to the utilisation of the 

approved product, meaning its installation, mounting or incorporation and not to its possible later use. 

2 Provisions concerning the construction of the product 

2.1 General 

The flexible double-walled pipes (jacketed hose lines with leak detection), a system conceived and made 

by the company Klenk, bearing the type designation DWSL, have to comply with the SPECIAL 

PROVISIONS as defined in this decision, including the data and details deposited with the German 

Institute for Construction Engineering. 

1 

Federal Water Act (Water Management Law, WHG) of 19 August 2002

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Z-65.25-220 

2.2 Characteristics and structure 

(1) The inner and outer hoses correspond to the type D or SD (i.e. with or without spring steel wire 

equipment) as specified in the standard DIN EN 12115 2 and the TRbF 131/2 3 (TRbF = Technical 

Regulations for Combustible Liquids). They must be suited for use within the scope of applications 

defined in above section 1. 

The same materials are used for both the inner and outer hoses. The hose material for the realisation 

of the internal layer according to Table 4 of standard DIN EN 12115 is to be chosen so that its 

suitability in view of the materials and the admitted liquid getting in touch with each other while 

conveying it through the pipe, is ensured. The same applies also in regard to the operating temperature 

of the pipe. The materials used for the manufacture of the hose fittings must, likewise, be suited for use 

in connection with the liquid to be conveyed. 

(2) The monitored space is realised using an intermediate layer consisting of thermoplastic 

poly(ether)ester elastomers following the specifications laid down in DIN EN 12115. This material is 

commonly known as Hytrel®. This intermediate layer consists of a plastic net that has been pulled over 

the inner hose. 

(3) The metal fittings and joints are made in compliance with DIN EN 14420 4 and tested as specified 

in DIN EN 12266 5 . 

(4) The sealants are made in compliance with DIN 3771, parts 1 to 5 6 and must meet the 

requirements specified in DIN ISO 1817 7 . 

(5) The mounting of the flexible double-walled pipe is to be realised in compliance with the mounting 

instructions deposited with the German Institute for Construction Engineering. 

(6) Proof of the functional reliability of the approved product has been furnished in compliance with the 

requirements specified in DIN EN 12115 and in the "Approval Principles specified for Leak Detectors 

for Double-walled (Jacketed) Pipes (ZG-LAGR)" issued by the German Institute for Construction 

Engineering (DIBt) in August 1994 and in the Technical Regulations for Combustible Liquids (TRbF) 

131, part 2, No. 5.7, in DIN EN ISO 8031 8 , DIN EN 14420, parts 1 to 6, and DIN 28450, DIN EN 1266- 

1/-2, DIN 3771, parts 1 to 5, plus DIN ISO 1817 with respect to the nominal size combinations 

according to Annex 2 hereto, 

2 DIN EN 12115:1999-08 Rubber and thermoplastics hoses and hose assemblies for liquid or gaseous 

chemicals – Specification; 

3 TRbF 131-2:1992-08 Technical Regulations for Combustible Liquids – Hose lines 

4 DIN EN 14420-1:2007-0 Hose fittings with clamp units - Part 1: Requirements, survey, designation and 

testing; 

DIN EN 14420-2:2005-05 Hose fittings with clamp units - Part 2: Hose side parts of hose tail; 

DIN EN 14420-3:2005-05 Hose fittings with clamp units - Part 3: Clamp units, bolted or pinned; 

DIN EN 14420-4:2007-04 Hose fittings with clamp units - Part 4: Flange connections; 

DIN EN 14420-5:2005-05 Hose fittings with clamp units - Part 5: Threaded connections; 

DIN EN 14420-6:2007-04 Hose fittings with clamp units - Part 6: TW tank truck couplings; 

5 DIN EN 12266-1:2003-06 Industrial valves - Testing of metallic valves - Part 1: Pressure tests, test 

procedures and acceptance criteria - Mandatory requirements; 

DIN EN 12266-2:2003-05 Industrial valves - Testing of metallic valves - Part 2: Tests, test procedures and 

acceptance criteria - Supplementary requirements; 

6 DIN 3771-1:1984-12 Fluid systems; O-rings; dimensions as in ISO 3601/1; 

DIN 3771-2:1984-12 

Fluid systems, O-Rings; testing, marking; 

DIN 3771-3:1984-12 

Fluid systems; O-rings; materials, field of application; 

DIN 3771-4:1984-12 

Fluid systems; O-rings; quality acceptance criteria; 

DIN 3771-5:1993-11 

Fluid systems; O-rings; methods for calculation and dimensions of housings; 

7 DIN ISO 1817:2008-08 Rubber, vulcanized - Determination of the effect of liquids (ISO 1817:2005) 

8 DIN EN ISO 8031:1997-08 Rubber and plastics hoses and hose assemblies - Determination of electrical 

resistance and conductivity (ISO 8031:2009);

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Z-65.25-220 

2.3 Manufacture and marking 

2.3.1 Manufacture of the approved product 

2.3.2 Marking 

The manufacture of the approved product must take place in the plants and/or factories, the names of 

which have been made known to and deposited with the German Institute for Construction Engineering 

(Deutsches Institut für Bautechnik, DIBt). 

The applicant must provide the flexible double-walled (jacketed) pipes with the conformity mark 

(Ü-mark) as required by the ordinances on conformity marks enacted by the different Federal States 

and must affix said mark(s) to the fittings existing at the end of the hose (flexible pipe). 

The application of any such marks is admitted only if the requirements specified in below section 2.4 

have been met. The flexible double-walled pipes need, apart from the marking required by 

DIN EN 12115, to be provided with the following indications in addition: 

- The type designation 

- The name of the manufacturer 

2.4 Proof of conformity 

2.4.1 General 

The applicant must furnish proof that the approved product complies with the provisions set out in this 

General Technical Approval with regard to applicant's factory by providing a corresponding declaration 

of conformance, which must base on the factory's production control and an initial type test performed 

by a recognised inspection agency authorised to perform such tests. 

2.4.2 Factory production control 

(1) The applicant, in his capacity as its manufacturer, must establish and carry out a factory production 

control system in his own works and must, beyond that, furnish proof that the assembled components, 

elements and parts of the flexible double-walled pipe comply with the construction documents that 

have been deposited with the German Institute for Constructional Engineering (DIBt). Factory 

production control in the above sense means permanent supervision and control of all steps needed 

for the production of the approved product. The purpose of the factory production control by routine 

item testing is to ensure that the flexible double-walled pipes comply with the specifications defined in 

this General Technical Approval. 

(2) The factory production control of the approved product is to be carried out in the applicant's 

manufacturing works by submitting all components and/or individual parts to an incoming control on the 

basis of acceptance test certificates as required in section 3.1 of DIN EN 10204 9 , which need to be 

prepared based on the following tests and controls: 

a) The inner and outer hoses of the flexible double-walled pipe are to be subjected to the tests and 

controls required by DIN EN 12115, DIN EN ISO 8031 and EN ISO 1402. 

If using flexible double-walled pipes for the conveyance of types of liquids, the flash point of which is 

below 55°C, proof with regard to the electrical characteristics of these liquids is to be furnished as 

required by DIN EN 12115. 

b) The intermediate layer is to be submitted to the AD test (dimension test) and the AR test 

(examination of the material certificates) as provided by DIN 3230-3 10 . 

c) Verification if the sealants tested in compliance with DIN 3771-3 and DIN ISO 1817 are suited for 

use within the scope of application indicated on the delivery note. 

9 DIN EN 10204:2005-01 Metallic products - Types of inspection documents. 

10 DIN 3230-3:1982-04 Technical delivery conditions for valves - Compilation of test methods.

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Z-65.25-220 

(3) The flexible double-walled pipes must, in addition to the controls and tests provided in Table 6 in 

the standards DIN EN 12115 and EN ISO 1402 11 , be subjected to at least the following tests and 

controls specified in DIN 3230-3: 

- AD test (dimension test) and AR test (examination of the material certificates); 

- BN test, including proof of compliance with the admissible leak rate 1 (test of the hose connection 

with water for leakproofness at the maximum allowable operating pressure (10bar)); 

- BQ test (test of the hose connection with water for leakproofness at the 1.5-fold maximum 

allowable operating pressure). 

In addition to the incoming controls, the connection fittings, including nipples and associated sealants, 

are, in the applicant's factory, to be subjected to the following tests and controls required by DIN 3230- 

3; 

- AD test (dimension test) and AR test (examination of the material certificates); 

Prior to using it for the first time, the flexible double-walled hose pipe assembly needs to be subjected 

to a leak test as provided by DIN EN 12266-1. The medium to be used for testing is gas. The test is to 

be realised by maintaining, at normal ambient temperature, test pressures of (6 ± 1) bar in the inner 

hose and of (6 ± 1) bar in the monitored space for at least 60 seconds. No bubbles must rise to the 

surface of the water if plunging the hose assembly into the water or, if coated with a special leak 

detection liquid, no continuous formation of bubbles must occur. 

(4) The results of the factory production control need to be recorded and analysed. The recordings 

must, at least, contain the following details: 

- Designation of the approved product; 

- Type of test or control; 

- Date of manufacture and testing of the approved product; 

- Results of the controls and/or tests; 

- Signature of the person responsible for the factory production control. 

The applicant must keep all recordings on file for at least five years. If requested to do so, they need to 

be submitted to the German Institute for Construction Engineering (DIBt) and/or the responsible 

supreme building control authority. 

Once the test results are insufficient, the applicant must immediately take all measures required in 

order to eliminate the related fault and/or insufficiency. 

Inner and outer hoses, intermediate layers, connection fittings, nipples, sleeves and associated 

sealants that fail to meet the requirements, are to be handled in such a manner that they cannot be 

confused with conforming components of the same kind. After elimination of the fault and/or 

insufficiency, the corresponding test or control must, as far as technically feasible and required as 

evidence that the fault and/or insufficiency has been eliminated, be repeated immediately. 

2.4.3 Initial type test of the approved product by a recognised inspection agency 

Within the limits of the initial type test, the requirements specified in DIN EN 12115, DIN EN 14420-1 

and in the "Approval Principles for Leak Detectors suited for use with Double-walled Pipelines" issued 

by the German Institute for Construction Engineering (DIBt) of August 1994, the Technical Regulations 

for Combustible Liquids (TRbF 131-2), in DIN EN 12266-1/2, DIN 3771-34 and DIN ISO 1817 have to 

be met. Once the results of the tests performed on samples from the current production underlying the 

General Technical Approval have been furnished, these will replace those obtained in the course of the 

initial type-testing procedure. 

EN ISO 1402:1996-09 

Rubber and plastics hoses and hose assemblies - Hydrostatic testing

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Z-65.25-220 

3 Design-related provisions 

(1) The utilisation of the flexible double-walled pipe and the associated intermediate layer is limited to 

the types of water-hazardous liquids of the suitability category A listed in the chemical resistance chart 

specified on the supplementary sheet 1 to DIN EN 12115 12 as suitable for use with the corresponding 

material. The approved product may also be used for the conveyance of other types of waterhazardous 

liquids if proof has been furnished that, if handled at the provided temperatures, these 

liquids meet the requirements specified in the Technical Regulations for Combustible Liquids (TRbF) 

131, part 2, No. 5.4. 

(2) To ensure the flexible double-walled pipe is monitored as required, the vacuum leak detector 

admitted for use with the related type of liquid specified in the Technical Description 13 is to be 

connected. Regarding the connection and operation of the vacuum leak detector, the instructions 

contained in the Technical Descriptions need to be followed and adhered to. 

(3) When using the product in exceptional cases for suction operations as admitted in below section 4, 

par. (7), the vacuum leak detector must be temporarily put out of operation. 

4 Utilisation-related provisions 

(1) The approved product is to be used in compliance with the specifications set out in the "Technical 

Description". Only specialised companies within the meaning of § 19, par. I, of the German Water 

Management Act (WHG) may be charged with the installation, maintenance and repair and/or cleaning 

of the approved product. They need to possess the knowledge required for the installation of leak 

detectors in compliance with the TRbF 503 (directive concerning the supervision of the installation of 

leak detectors, version dated May 1987) and must have been trained by the applicant. This training is 

to be repeated annually. Each time after an inspection of the leak detector, the expert charged with 

doing this work must issue a corresponding installation and test certificate. 

(2) No specialised companies need to be charged with the execution of the works and activities 

specified in above sub-section (1), if they, as an exception under German Federal State Law, are 

exempted from the obligation to register as certified specialists or if the manufacturer of the approved 

product carries out these works and/or activities using his own qualified staff. In such a case, the 

application of the occupational safety and health requirements remains unaffected. 

(3) Leak detection systems working on the vacuum principle only may be connected to the flexible 

jacketed pipe. In the case of a leakage, the leak detector must be able to withstand overpressures of up 

to 10bar or must trigger automatic (self-acting) shut-off valves (magnetic valves, f. ex.) to prevent its 

components from being exposed to inadmissible pressure levels. 

(4) The vacuum leak detector must comply with the applicable legal provisions and its suitability for 

use with the flexible double-walled pipe within the scope of application it has been designed for must 

have been proven. At the latest when reaching a negative pressure of -325mbar, the vacuum leak 

detector must trigger an alarm. Once such an alarm is triggerd, the leak detector must deactivate the 

vacuum pump to discontinue the vacuuming procedure. 

(5) The liquids provided for being transferred must not have a tendency to thicken or to separate solid 

materials and their kinematic viscosity should not exceed 5000cSt at +4°C. 

Supplementary sheet 1 to 

12 DIN EN 12115:2001-05 Rubber and thermoplastics hoses and hose assemblies for liquid or gaseous chemicals - 

Specification; 

13 

Technical Description of the double-walled hose line manufactured by the applicant as examined by TÜV-Nord 

Systems GmbH & Co. KG on June 19, 2009.

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Z-65.25-220 

(6) The flexible double-walled pipe must, at one of its ends, be provided with a nozzle for the 

connection of the leak detector. The other end of the flexible double-walled pipe needs to be provided 

with a control-screw that allows to check if the leak detection medium can pass freely. 

(7) Only in exceptional cases may the flexible double-walled pipe be used for suction operations. This 

is admissible if, as specified in DIN EN 12115, the possible negative suction pressure with respect to 

the actually applied hose, suffices to ensure the vacuum stability in an acceptable manner. 

(8) The bolts used for the fixing of the flexible double-walled pipe, including connection fittings and 

nipples need to be protected against accidental loosening. 

(9) If using the approved product for the conveyance of types of liquids, the flash point of which is 

below 55°C, or if using it in explosion hazardous areas, the requirements for its electrical conductivity 

characteristics specified in DIN EN 12115, including the guidelines issued by the employers' liability 

insurance association for preventing ignition hazards resulting from electrostatic charge, need to 

followed an complied with. The manufacturer is obliged to provide corresponding evidence. If using the 

metal insert of the pipe for connecting it with the hose fitting, proof is to be furnished that, while 

integrating the pipe into an overall system, the electrical contact between the metal inserts and the 

hose or pipe fitting(s) is absolutely perfect and works faultless. 

(10) Regarding each flexible double-walled pipe, a corresponding installation and test certificate is to 

be produced. 

5 Provisions regarding use, maintenance and care, including recurring 

checks and inspections 

(1) The applicant must include the Technical Description in his delivery. 

(2) The usability of the approved product is to be reconsidered and checked recurrently at reasonable 

intervals, but at least once every year. During the first start-up / commissioning of the flexible doublewalled 

pipe system and also the recurring functional checks, the unobstructedness and free passability 

of the monitored space between the inner and outer hose is to be checked by opening the controlscrew 

provided for this purpose and checking the pressure change occurring within the monitored 

space. It is the responsibility of the operator to decide in what manner and at what intervals the checks 

are to be made within the above-specified timeframe. 

(3) The admissible leak detectors connected to the monitored space between the inner and outer hose 

need to be checked in compliance with the Technical Description established for the corresponding 

device type. 

(4) All checks, inspections or tests prescribed under different laws shall remain unaffected. 

Eggert 

Certified

Pages 9 to 12 (non editable technical drawings) 

As for the translation of the texts on these drawings, please refer to the separately attached 

MS Word document or corresponding printout.

Annex 2 to the General Technical Approval No. Z-65.25-220 dated 27 July 2009 

Technical characteristics and materials used with combined nominal hose sizes 

Type name 

designating 

the combined 

nominal hose 

sizes 

Sizes of 

inner hoses 

Sizes of 

outer hoses 

Monitored 

space, 

volume in 

litres / m 

Design of connection 

and drawing No. 

Metals used with the fittings 

DWSL 1 DN 15 DN 32 0.424 With union joint Screw connections made of brass (Ms58) or stainless steel 

(1/2") (1 ¼") Piece list dated 29/10/2008 Pinned clamp fitting made of aluminium 

Drwg No. 1-2-5/1_0 Stainless steel socket (connecting piece on the hose side) 


(3/4") (1 ½") Piece list dated 29/10/2008 Pinned clamp fitting made of aluminium 



(3/4") (1 ½") Piece list dated 29/10/2008 Screwed clamp fitting made of aluminium 



(1 ½") (2 1/2") Piece list dated 29/10/2008 Screwed clamp fitting made of aluminium 


DWSL 5 DN 40 ON 65 1.080 With union joint Screw connections made of brass (Ms58) or stainless steel 

(1 ½") (2 1/2") Piece list date 29/10/2008 Screwed clamp fitting, pinned, made of aluminium 



(2 ½") 

") 

(4") Piece list dated 29/10/2008 Screwed clamp fitting made of aluminium 


DWSL 7 DN 50 DN 75 0.89 With tanker coupling Made of brass (Ms58) or stainless steel 

DWSL 8 (2") (3") Piece list dated 18/03/2009 Screwed clamp fitting, pinned, made of stainless steel or aluminium 

Drwg No. 7-8NM_0 Stainless steel socket (connecting piece on the hose side) 

7-8/3_0 

7-8/2_0 

With flange connection 

Piece list dated 28/10/2008 

Drwg No. 7-8/F_0 

7-8/1_0 

7-8/2_0 

DWSL 9 DN 75 DN 100 1.075 With tanker coupling Made of brass (Ms58) or stainless steel 

plus 

DWSL 10 

(3") (4") Piece list dated 28/10/2008 

Drwg No. 9-10/VM_0 

Pinned clamp fitting made of stainless steel or aluminium 

Stainless steel socket (connecting piece on the hose side) 

9-10/3_0 

9-10/2_0 

With screwed flange connection 

Piece list dated 28/10/2008 

Drwg No. 9-10/F_0 

7-8/1_5 

7-8/2_0

General Technical Approval

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