Purpose, layout criteria:
Guarantee of operational and working safety, elimination of accident risk, no or minimised impairment of the hygienic situation in the reservoir. Additionally:
- low investment costs
- low operational costs
- high reliability
- easy maintenance and cleaning
- elimination of accidents
- easy handling and cleaning
- no impairment of the hygienic situation
Benefits for water suppliers:
- reduced risk of bacterial germination
- increased safety for compliance with potable water ordinance
- reduced operational costs
All internals and building elements of a drinking water reservoir should
- least possibly disturb the flow (e.g. stairs)
- not create any hygienic loads (e.g. gaskets)
- comply with accident prevention regulations (e.g. DVGW)
Important criteria have to be complied with from the hygienic view:
- KTW recommendations
- DVGW, sheet W 270
For operational safety, all access ways needed for control purposes must work reliably. Constructional design should further ensure that regular cleaning cycles will run easily and trouble-free.
Function of individual components:
- Pressure door: Comfortable water chamber access for cleaning purposes
- Stairs: No accident risk; filigree design which does hardly disturb the flow. Also the installation position plays a roll; no water must remain in the water changing zone but should run off without problems.
- Railing: Similar to stairs; Special attention must be paid to closing the hollows in the post area.
- Ladder: Similar to railing; Additional personal safety gear has to be provided for entrance depths bigger than 5 m.
- Wall duct: A connection to the concrete without hollows is absolutely necessary, not only for tightness but also for hygienic reasons.
- Gaskets: Gaskets shall comply with KTW recommendations and W 270.
- Material: As per DVGW sheet W 311 all components which are in direct contact with water have to be made of austenitic stainless steel class 1.4571, components above water surface may also be made of 1.4301 stainless steel providing the incurring amounts of condensate and chlorine gas are small. A plain surface of quality IIIc facilitates cleaning. All welding work is done in our factory under an inert gas atmosphere followed by acid-treatment in a pickling bath and passivation. Only easy to remove screw connections are used on site to make possible cleaning work easy. The plain material surface prevents deposits and is a poor culture medium for germs. The material's high corrosion resistance guarantees long life and high economic efficiency of the investment. Attention must be paid to electrolytic separation when combining stainless steel with other metals.
Options for connection:
- Stainless steel lining: Tight and stable welding connections are possible when considering the guidelines for processing stainless steel.
- Foil lining: All tank ducts have to provided with foil flanges. Damaging of the foil by a sharp pointed object has to be avoided.
- Concrete lining: Hollows between original tank surface, lining and wall ducts have to be avoided. This requires proper workmanship and can be facilitated by a S-shape frame.
by Stefan Wittl