Thyssenkrupp Steel Europe has opted for Schroeder pump protection valves during the recent overhaul of Unit 4 of its power station in Duisburg. The valves that were installed previously from another supplier repeatedly caused problems because the minimum flow control was carried out by two valves. This design often led to an increase in the drive power requirement and a drop in overall efficiency. So Thyssenkrupp Steel looked for a better solution. The required valves had to have a nominal size of 125 mm for the electric pumps and 200 mm for the turbo-pump, and a nominal pressure of PN 630 bar.
Thyssenkrupp Steel decided on the automatic minimum flow system of the SMA series manufactured by Schroeder Valves. These are high-pressure valves, which automatically protect centrifugal pumps against damage that may occur as a result of the partial evaporation of the pump content when the pumps are operated under low load. As soon as the main pump flow falls below a predetermined value, the valve opens the bypass and safely drains the minimum volume, even if the pumping volume in the main flow direction drops to zero.
The bypass is always completely opened or closed through its pilot-controlled valve piston. This on/off control makes it possible to increase the load limit of the valves up to 630 bar (pumping pressure). The preferred utilisation range is thus between PN 250 and PN 400 or ANSI CLASS 2500. The bypass amount may be up to 35% of the main pumping volume. The minimum quantity can be up to 12 percent of the full-load delivery rate.
The Schroeder SMA valve is a compact system that combines the performance formerly achieved by the two built-in valves so that a second valve is no longer necessary. Thyssenkrupp Steel chose Schroeder Valves because of the proven track record of reliability, durability and extremely low maintenance in other plants. This is due to the construction and the high-quality materials used in the valves. In the event that maintenance should be necessary, Schroeder Valves has attached particular importance to the ease of maintenance: for the replacement of wearing parts such as pistons and seat rings, it is not necessary to remove the minimum flow line or even the complete valve.
There are hundreds of Schroeder Valves installed in plants in southern Africa with repairs and reconditioning provided by the Vereeniging and Durban Valve Repair Centres.
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