Enamelling – secret ingredient for successful use
Today, more than 130 million m³ of purest drinking water flow annually through a 1,700 km long pipeline network from Lake Constance to the Odenwald forest. The 183 members of the Zweckverband Bodensee-Wasserversorgung (towns, municipalities and other special-purpose water supply associations) supply 320 municipalities with around 4 million inhabitants with drinking water from Lake Constance – safely and reliably, day and night, 365 days a year and has been for 60 years. The valves installed there, with pipe diameters of up to DN 1600, are designed for pipeline pressures of up to 30 bar and are partly equipped with drop-weight actuators. They are used, among other things, for pipe rupture, overflow and leakage protection.
Treatment of raw water with ozone
The high-quality raw water of Lake Constance is disinfected during the treatment process by the addition of highly active oxygen (ozone / O3). The ozone oxidizes dissolved and particulate organic substances, killing or inactivating any microorganisms still present. The ozone is produced from pure oxygen (O2) immediately before it is added to the water. For this purpose, the oxygen is converted into ozone in so-called tube ozone generators. Injectors transport the ozone into the water, mixers distribute the tiny ozone bubbles evenly throughout the entire water body. The water then remains in large containers for at least 2 hours; during this time, disinfection takes place.
Higher demands on valves due to climate change
The constant climate change, which also affects the ecosystem of Lake Constance, also poses challenges for the Lake Constance water supply and meanwhile requires an increase in the ozone addition to an average of 0.2 to 1.4 mg/l. The ozone concentration of Lake Constance water is also increasing. This in turn places increased demands on the valves used, which are in direct contact with the ozone-enriched water, in terms of materials and corrosion protection. ERHARD was able to meet these high requirements by installing the double eccentric “ROCO Wave” butterfly valves in the “enamelled inner body and disc” version. The advantages of the enamelled coating are obvious:
- high corrosion protection as the key to maximizing service life
- perfect hygienic conditions thanks to the smooth surface of the enamel components (Ra 0,05)
- residual substances in the water, as well as oxidized organic components of microorganisms, have difficulties to accumulate on the fitting, which contributes to the maintenance of water purity
- reduction of pressure loss due to extremely smooth surface, which increases efficiency and reduces energy consumption
- existing connection also under bending or other loads, such as internal pressure or pipeline forces
Butterfly valves of nominal sizes DN 1200 and DN 1400 in pressure stage PN 10 and seals in EPDM (DVGW, KTW) were used for installation in the intermediate tank east/west of the ozone plant.
The enamelled version has proven itself over the last 20 years against other coating systems with regard to contact with ozone-enriched water and in particular as protection against deposits by microorganisms or aquatic neozoa and is therefore set as standard by the Lake Constance water supply in ozone-polluted areas.
Enamel pioneer and professional for decades
ERHARD was one of the first manufacturers of enamelled fittings in the 1970s. In the 1980s, enamel was already established as a coating for drinking water as an integral part of the ERHARD product range. With increasing know-how, the refinement of the enamelling process and its application to fittings also increased.
To this day, the company works closely with its suppliers to develop ever better and more durable enamel coatings that do not crack under load. With ERHARD Pro-Email, the most important innovation of which is the development of a special fibre enamel, which is particularly suitable for use in the water industry due to its incomparable impact strength, the company today relies more than ever on the advantages of enamelling for the customer.
Authors: Daniela Usenbenz, Matthias Müller, ERHARD GmbH & Co KG