The servo system controls the differential cylinders of beam and chain conveyors in steel works and rolling mills using electrohydraulic direction valves and through valves. A four-way proportional valve (11) with an electrohydraulic pre-control valve (12) and a hydraulic main valve (13) is used as direction and through-flow control element and is installed at a distance (up to 25000 mm) from the hydraulic drive (4), e.g. in the control panel, and connected via pipes (7,8) to the drive. The pre-control valve of the four-way proportional valve is installed a relatively long way from the drive whilst the main valve may be near the drive, the two valves being connected by pipes.
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