The special features of drinking water seals

Drinking water seals play a crucial role in ensuring the safety and quality of drinking water. (Source: AdobeStock / HappyRichStudio)

Drinking water seals play a crucial role in ensuring the hygiene and integrity of the drinking water system. These specialised seals are designed to prevent contaminants from entering the water system while ensuring that water does not leak under the various pressure conditions within the system.

The choice of material for drinking water seals is of crucial importance, as not all materials are suitable for contact with drinking water. The materials must not only fulfil mechanical requirements such as pressure resistance and flexibility, but must also be chemically inert so as not to release any harmful substances into the water. Commonly used materials include special elastomers and plastics that have the relevant certifications confirming their suitability for contact with drinking water.

Drinking water seals must meet the highest hygienic standards. This means that the materials from which they are made must be resistant to microbial growth. Bacteria, mould and algae can multiply rapidly in humid environments and it is therefore important that the seals are designed to minimise such risks. Materials with antibacterial properties or those that allow easy cleaning and disinfection are often chosen for this purpose.

Mechanical load capacity

Drinking water seals must be able to withstand the various pressure conditions to which they are exposed. This includes not only the normal operating pressure, but also potential pressure peaks that can be caused by the rapid closing of valves or pump starts, for example. The mechanical resilience of the seals is therefore a key factor in the longevity and reliability of the entire drinking water system.

The KTW-BWGL stands for “Assessment basis for plastics and other organic materials in contact with drinking water” and is a set of regulations published by the Federal Environment Agency (UBA) in Germany.

The installation of drinking water seals requires a high degree of precision in order to avoid leaks and potential contamination. Seals often need to be adaptable to complex shapes and different pipe diameters. Ease of installation and maintenance, without compromising the integrity of the drinking water, is also an important consideration. In addition, seals must be designed to provide long-term sealing performance without regular replacement, which not only increases the reliability of the system but also reduces operating costs.

Environmental and health protection

In addition to the direct requirements for drinking water seals, the protection of the environment and human health also plays an important role. The materials used must not release any harmful substances into the water and must also be environmentally friendly. Regulation and monitoring by the relevant authorities and certification bodies ensures that only seals that meet the strict guidelines for drinking water systems are used.

The Federal Environment Agency (UBA) has drawn up specific specifications for a large number of components in the drinking water supply. The KTW-BWGL (Assessment basis for plastics and other organic materials in contact with drinking water) serves as a decisive standard for soft fibre seals. This guideline evaluates products and components made of organic materials with regard to the raw materials used and the potential of these substances to migrate into drinking water.

The raw materials that may be used for the production of elastomers in contact with drinking water are listed in the UBA's positive list. This list also applies to fibre-reinforced sealing sheets bonded with elastomers (FA - fibre-based sealing sheets). Part 1 of the list contains the fully evaluated substances (monomers, fillers, plasticisers, anti-ageing agents, processing aids, cross-linking agents, etc.). The positive list Part 2 lists substances that have not been fully evaluated. The use of these partially evaluated substances was only accepted until 31 December 2021. A transitional period still allows some time, but the switch to new sealing materials consisting only of fully assessed substances is inevitable.

Drinking water seals must fulfil special requirements for water bubblers. (Source: AdobeStock / Alex)

The supply chain must respond

For the manufacturers of FA sealing sheets, this situation means that the previous formulations for products intended for drinking water applications may no longer be used in this area of application. It is painful that the previously familiar range of applications is no longer guaranteed due to the restriction of possible ingredients. This particularly affects further processors, such as punchers and technical dealers, who have to reorganise themselves with regard to the utilisation of the sealing sheets during punching and with regard to storage for different areas of application (e.g. drinking water, gas, temperature ranges, etc.) (storage and calculation).

It could also become a problem for valve, pump and appliance manufacturers if it is not possible to allocate different seal materials to different areas of application in production (e.g. heating appliances with seals for gas as well as heating and drinking water) and the “one for all seals” is no longer available. Despite the transitional regulation, all this means that users and the supply chain should look for a well-functioning alternative at an early stage.

Seals for water treatment and sparkling water devices

In water purification and sparkling water appliances, the transition between the valve of a carbon dioxide cartridge and the pressure-reducing valve on the appliance itself must be reliably sealed. A seal manufacturer developed a now patented seal made of high-performance polyurethane for a customer. Thanks to its special geometry, this not only equalises the different valve dimensions on the various gas cartridges. It also ensures a high level of tightness under permanent pressure.

When developing the appliance, the customer initially faced a technical challenge. The valves of common carbon dioxide gas cartridges are not fully standardised and have different connection heights. To ensure that all valve variants fit together with the appliance without any problems, a seal with a special design is required that seals reliably despite this high tolerance range.

Freudenberg Sealing Technologies developed a now patented seal made of high-performance polyurethane for a customer. (Source: Freudenberg Sealing Technologies)

“After the customer contacted us, we gradually got to grips with the special requirements that such a seal has to fulfil”, reports Ulrich Wüstenhagen, Product Development Pneumatics at Freudenberg Sealing Technologies. “It quickly became clear that this project required both our material expertise and our development know-how and experience in the manufacture of such products.”

Material found for seal

Due to the tight time frame, there was not much room for extensive test series. By utilising the existing development and material expertise in-house and in close cooperation with the appliance manufacturer, the experts at Freudenberg Sealing Technologies not only found the optimum seal design in a very short time, but also a suitable material: the high-performance polyurethane 93 AU V167 is hard-wearing and has excellent tensile strength in addition to high elongation at break. It is highly elastic, wear-resistant and approved for food contact in accordance with Regulation 10/2011 of the European Union. It also fulfils the requirements of the FDA and 3-A Sanitary Standards.

The company's own service provider Freudenberg Xpress® supplied the first CNC-turned prototypes and then took over the production of two pilot series of around 1,000 CNC-turned seals each. In the next step, the expertise of the specialists at Freudenberg Sealing Technologies was required for the production and sampling of an injection mould, from which the series parts are now supplied directly in a cost-effective, “ready-to-use” form. “Thanks to a very pragmatic approach, together with our customer we managed to come up with a customised solution in a short space of time, which has now even been successfully patented”, summarises Wüstenhagen. “So that tap water can be enjoyed without hesitation anywhere in the world in future.”