Articles| Firma Klinger

Dipl.-Ing. Norbert Weimer Management - Business Unit Manager Gasket Plates

New conformities and approvals for drinking water sealing according to KTW-BWGL

The KTW-BWGL has introduced a new regulation that significantly impacts the handling of sealing materials in drinking water. The effects specifically on commonly used fiber-based (FA) sealing materials and the resulting consequences for practical applications are substantial. For instance, manufacturers of FA sealing plates are no longer allowed to use their previous formulations for products intended for use in drinking water applications under this regulation. The KLINGER Group provides a solution to address these new challenges with its fiber-based gaskets

The German Federal Environment Agency (UBA) has established requirements for various components in the field of drinking water supply. In the realm of fiber-reinforced soft gaskets, the KTW-BWGL (Assessment Basis for Plastics and other Organic Materials in Contact with Drinking Water) is authoritative. Products and components made of organic materials are evaluated concerning the raw materials used (pre-materials) and their transfer of substances into drinking water.
The UBA's positive list includes the raw materials permitted for the production of elastomers in contact with drinking water. This list also applies to fiber-reinforced sealing plates bound with elastomers (FA - fiber-based sealing plates). Part 1 of the list comprises fully evaluated substances (monomers, fillers, plasticizers, aging inhibitors, processing aids, cross-linking agents, etc.). Part 2 of the positive list includes substances that have not been fully evaluated. The use of these partially evaluated substances was accepted only until December 31, 2021.
While a transition period allows for some leeway, the switch to new sealing materials composed solely of fully evaluated substances is inevitable.

The supply chain must respond

For manufacturers of fiber-reinforced (FA) sealing plates, this situation implies that the existing formulations for products intended for use in drinking water applications are no longer permissible in this application area. It is regrettable that the previously accustomed versatility is no longer guaranteed due to the limitation of possible ingredients. This particularly affects downstream processors, such as stampers and technical distributors, who need to reorganize their practices concerning the utilization of sealing plates during stamping and regarding the storage for various applications (e.g., drinking water, gas, temperature ranges) – both in terms of inventory management and cost calculation.
Likewise, it could pose a challenge for valve, pump, and device manufacturers if the production entails an inability to assign different sealing materials to various application areas (e.g., appliances requiring seals for both gas and heating or drinking water), and the concept of a "one-size-fits-all" seal is no longer available. Despite the transitional provisions, all of this underscores the importance for end-users and the supply chain to proactively seek a well-functioning alternative. In response to these challenges, the KLINGER Group now provides a solution to alleviate this problem.





Klingersil c-4400

klingersil c-4240











Compressive sand strength DIN 52913

50 MPa, 16h/175°C




Stability according to KLINGER 50 MPa

Thickness decrease bei 23°C




Stability according to KLINGER 50 MPa

Thickness decrease bei 200°C





DIN 28090-2

mg/(s x m)



Thickness swelling ASTM F 146

ÖL IRM 903: 5h/150°C




Thickness swelling ASTM F 146

Fuel B: 5h/23°C





DIN 28090-2




Flat gaskets based on fibres

The sealing type FA (fiber-based sealing materials) is frequently utilized in drinking water systems. It is primarily affected by the new KTW-BWGL regulation due to the binder (elastomer) it contains. On one hand, it serves as the standard seal for the drinking water sector, but on the other hand, it faces significant restrictions in terms of raw material selection under this regulation. The reduction in allowed ingredients for the production process is so substantial that the rolling and vulcanization process demands the highest level of expertise to manufacture a sealing plate under these conditions.
According to information from KLINGER, the company currently offers the only available product in the market that complies with the requirements of the KTW-BWGL, namely the sealing KLINGERSIL C-4240 (Image 1)

Image 1: Manufacturers of FA gasket sheets have to change their previous formulations for products intended for drinking water applications – including the flat gaskets of the KLINGER Group.

Reliability is also important in assembly

In the field of drinking water installation, two distinct application areas can be identified. In one scenario, the technician, equipped with a service vehicle, visits customers and, under often challenging conditions, replaces or installs components on-site, relying on their experience and craftsmanship. The other application area involves the industrial production of composite components and devices, ranging from water filters, valves, and pumps to heating appliances. Here, precise assembly conditions and high repeatability of assembly processes are expected.
Therefore, the sealing material must possess consistent quality to ensure industrial manufacturing with a consistent performance. Additionally, it must have a broad application range to facilitate manual assembly under various conditions. KLINGER has developed the KLINGERSIL C-4240 sealing plate, which behaves similarly to their previous sealing materials. This behavior allows users to implement the new sealing material without specific adjustments. The compression behavior and stability are as desired by the user. A comparison with the previous KLINGERSIL C-4400 illustrates this (Table 1).
Despite the challenges in producing a well-vulcanized product due to extremely reduced cross-linking chemistry, the results are promising. Examining the pressure resistance curve according to DIN 52913 reveals the stability of the sealing material's behavior: the adaptation process to the applied pressure only lasts until the test temperature is reached, after which the material remains stable throughout the rest of the testing duration (Image 2).
The compression set curve according to EN 13555 also demonstrates a uniform deformation progression without a "Crashpoint" up to a limit load of 200 MPa. To put it in perspective, the material's capability to withstand a load of 5 tons on a 3/4" gasket with dimensions of 24 x 16 mm gives a better understanding of its performance (Image 3).

What approvals and certificates does the new sealing material offer?

In recent years, the process of testing sealing materials at institutes and organizations to obtain corresponding certificates has become quite time-consuming. Therefore, information on these certifications becomes available gradually for a new product. After completing the assessment for drinking water hygiene according to the Elastomer Guideline and DVGW Worksheet W 270 in 2021, KLINGER was able to provide proof of tightness for use in gas applications in 2022. The DIN-DVGW type approval certificate according to DIN 3535-6 for use in gas applications is available.
As of the year 2023, KLINGER has also secured the English drinking water approval from WRAS and a statement of compliance with EU Regulation 1935/2004. Even conformity with the redesigned BfR is confirmed.
For manufacturers of devices for hot water generation, having these certifications is a significant advantage. It can be challenging to distinguish between seals for drinking water and seals for the gas-carrying parts in mass production. Similarly, the wide range of approvals and conformities is beneficial for stampers and technical distributors, allowing them to make better use of the sealing plates due to the additional application possibilities

Users need to initiate a changeover process

For responsible manufacturers and distributors of valves, pumps, and devices in the field of drinking water applications, the urgency to initiate the transition process towards the officially required sealing quality is increasing. Especially for industrially produced components, devices, and systems, action must be taken now to successfully complete the transition process before the final deadline. Even for components and devices requiring new certifications, the necessary evidence can be easily provided with KLINGERSIL® C-4240.

Dipl.-Ing. Norbert Weimer

Management - Business Unit Manager                                Gasket Plates

65510 ldstein
Tel.: +49 6126 4016 20