| 摘要 |
The hydraulic drive, which has a pump unit, a volume controlling valve and a cylinder-piston unit (11), also comprises a control device with a directional control valve (28) which is arranged downstream of the volume controlling valve (29) and the control piston (30) of which is centred in its centre position by springs (33). Each of the two sides of the control piston (30) is connected via a respective control line (38, 39) to a pilot control valve (21). In order in a simple manner to limit the accelerations of the driven parts and set correspondingly different mass flows in opposite directions of movement, each of the two control lines (38, 39) has two parallel branches, each of which contains a throttle valve (24, 26, 23, 25) and, in series therewith, a non-return valve (27). In each of the two control lines (38, 39), the direction of flow through the non-return valve (27) of one branch is opposite to that through the non-return valve (27) of the other branch. The two pump-side control edges of the main control piston are formed by chamfers (31, 32) which correspond to a predetermined change in the mass flow via each of the two selectable paths. The drive is suitable, for example, for the slide gate nozzle of a Siemens-Martin (open hearth) furnace. <IMAGE>
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