Some Reactor or Turbine parts that interact with external blocks are available in a passive or active form, or both.
A passive part does nothing by itself. It does not try to send out energy, fluids, or items, nor does it try to acquire them. The block connected to the part needs to take the initiative and start the transfer.
An active part is always looking for an opportunity to extract items and fluids or to send out power, items, and fluids to the connected block, but it does not allow the connected block to insert or extract anything from the part.
By mixing active and passive parts, you can fine-tune your resource distribution and acquisition network.