Day after day, wastewater is produced in huge quantities. Before it can return to the natural cycle, it must be thoroughly reprocessed in sewage treatment plants. Pumps, mixers, aerators and other machines are used for this purpose. They perform a wide variety of tasks in separation, filtration and treatment.
Mechanical seals are used at many points in these processes, which have to meet high requirements, especially with regard to corrosion resistance and suitability for solids.
For the treatment of industrial process water in a closed circuit, the demands on the mechanical seal used are also high. Depending on the application, the water is contaminated with various types of substances.
The highest requirements apply to the area of drinking water supply. In the interest of consumers, the relevant regulations must be observed – a wide variety of pumps are involved in the production of clean drinking water, including double-bearing, multistage pumps and vacuum pumps, which are often sealed with single-acting mechanical seals. In contrast, double-acting mechanical seals are mainly used for higher vacuum.
The result is innovative, in some cases customized solutions for the special requirements of water, wastewater and sewage treatment plants, based on decades of experience in the industry.
Extreme operating conditions and highest requirements
Innovative, often customized solutions based on decades of experience in the industry with well-founded application technology expertise.
Sustainable optimization of centrifugal pumps in large sewage treatment plants.
Insufficient service life when sealing digested sludge with 3.5 % dry matter (DS) and sand content was the reason for the conversion to CHETRA metal bellows mechanical seal, type 700. This single mechanical seal has a corrosion-resistant lamella bellows made of Inconel (T.M. Cabot) with “self-cleaning effect”. The elimination of spring(s) – by the bellows – makes this mechanical seal largely insensitive to deposits and contamination.
Further measures to improve economy: Only occasional water flushing – every 2-4 weeks for 1-2 minutes – instead of the previous permanent flushing with high fresh water requirement.
In some mechanical seals, water flushing is dispensed with completely by grease lubrication at the respective stuffing box (sealing chamber). Occasional desserts using a grease gun. The average service life of a mechanical seal of type 700 in these applications is 10 years.
Problems with leaks solved to our complete satisfaction.
In a steelworks in the coking plant, problems were encountered when sealing the pumps with so-called “tar water” due to the high level of contamination (leakage) in the vicinity of the plant and limited service life of the seal. The tar water is corrosive and contains solids. An additional complicating factor for the seal was the design of the pump used: double bearing without fixed bearing. This meant that axial movements of +/-4 mm had to be accommodated.
The CHETRA single mechanical seal type 201, in stationary design and in pre-assembled cartridge version, was designed to meet the requirements in terms of construction and materials used. Solid (non-shrunk) tungsten carbide/seal rings and counter rings and PTFE secondary seals are used. Springs and other components made of CrNiMo steel. The operation has also been improved by appropriate circulation guidance. Result: “leakage-free” operation – with service lives of > 3 years.
CHETRA mechanical seal was the only unit to withstand the accident.
Conversion of all cooling water pumps in Brazilian nuclear power plant (cooling water circuit) to split mechanical seals (GLRD). Special requirements: Resistance to seawater and shell limestone and compliance with all nuclear-relevant regulations, such as KTA 1401, QSP 4a and TÜV approval After approx. 1 year it became apparent after an accident that the installed mechanical seal type 299 was the only component that had remained undamaged. Meanwhile service lives of 5 – 6 years have been achieved.
The safety reserves built into CHETRA GLRD have also proved their worth. The stationary design and the special conception of the “split” design of the mechanical seal type 299 allow the operation of this “split” seal in vacuum up to 0.5 bar abs. and up to pressures of max. 25 bar – considerably above the conventional application range of split seals.
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