Functioning shut-off valves in the main and in trunk mains are major technical components in water supply. They are built-in at relatively large intervals, a further shutoff beyond one of these devices is sometimes very difficult. Basically, there are two kinds of valves: - Ellipso-valves (in use since 1873) with different drives, design and bearing, and
- Shut-off valves (in use since 1960) of different construction and design.
Both valves must be smoothly operable and tight. Searching for spare parts for outdated valves
Cast and seal parts of ellipso-valves have corroded in the course of many decades, material fatigue has set in and they risk to break. A prerequisite for starting repair works was to have workshop drawings of valves, some of which were more than 120 years old. To this day, the competent waterworks only have a few precise type designations left.
An attempt to repair these valves - a DN 950 mm weighing for example 6.300 kg, the valve wedge itself 800 kg - was therefore limited to a few types. Manufacture of spare parts is practically impossible and to attempt repair without knowing the construction principle is rather risky with regard to safe water supply and working safety.
The repair crew enters through man-holes
However, after difficult investigations in archives in Vienna and Budapest and with the manufacturing companies or their successors it was possible to find workshop drawings of ellipso-valves and butterfly flaps still used by the Vienna Waterworks.
This will considerably facilitate not only repair works, but also the preventive manufacture of typical wearing parts. The main problem of butterfly flaps is wear or damage of the rubber seal ring along the flap plate.
Since this rubber ring is on the flap plate inside the pipe, hardly any repairs were made. Some years ago, the Vienna Waterworks began to repair the rubber seals in those places, where so-called man-holes allowed access to the previously evacuated pipe.
In the beginning, the rubber was left in its place, the pressing power on the locking collar was increased and thus - after smoothing the seal bed - tightness was achieved.
Since the existing rubber seals could not resist the mechanical strain, new seal rings were developed. They are one the one hand made of more robust materials (the synthetic material Vulkolan), on the other, better fitting between sealing and sealing surface improves durability.
It was also necessary to find a way to carry out leak tests in built-in parts. Micro-adjustment is effected by means of tests with paper strips or back-light.
Only two butterfly flaps between crew and water
Since crew members have to go inside the pipes both during repair works and in leak tests, the sections on both sides of the butterfly flaps have to be sealed-off and empty.
For safety reasons it is also necessary to close also the next shut-off valve in case a valve should break. Similarly, every valve, that is removed due to system changes is immediately subjected to a general check-up. These shut-off valves can be fitted in again as practically new seal and control devices.
To this day, it was possible to avoid removal by repair works in situ in 160 cases. About 10 valves were removed and their full functioning restored in the workshop.
Cost analyses have shown that the complete exchange of a DN 800 valve is over 40 times more expensive than underground repair. Repair works are carried out by a so-called "Schieberpartie" (a small crew of experienced specialists of the Vienna Waterworks) working in the pipe system.
A synoptic table of the Vienna water pipe system was created to improve the efficiency of repair works of main valves. They are displayed on push of a button according to their design.(Source: aqua press int. 01/99)
Anton Klas
Information & Contact:
Anton Klas,
MA 31 - Wiener Wasserwerke,
A-1060 Wien, Grabnergasse 4-6,
Tel. +43/1/599 59-0,
Fax +43/1/599 59-7231
