Don't know what version of 3CX you have, but in general, with a "double" pump such as fitted to the early models, you have a large bore feed and two outputs. The one nearest the engine feeds the main hydraulic system, while the front one feeds the extending dipper arm. As the pump is one unit, both sections will be outputing all the time the engine is running, so I would say no you can't blank one off (not at the pump anyway).
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