| 摘要 |
The valve has a main control piston (4) displaced in one or other direction acting as the second valve stage. A pre-control stage is provided for the control piston (4) acting as the first valve stage. The axially displaced control piston (4) has an internal bore (9) containing a pre-control piston (11). The pre-control piston is rotatable by a stepping motor and has helical edges which are used to control the feed into the bore (9) and the discharge from the bore (9). One face (8) of the main piston (4) is supplied with a constant control pressure and its opposite face (10), which is double the size, is supplied with the controlled pressure provided by the pre-control piston (11).
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