The dart sub is a specially profiled sub run down by the BHA. The dart is dropped in either when the bit is at the shoe when tripping out, or if things have gone squirly and you want to shut the ID of the drill pipe off.

You drop the dart in and can pump down if need be. They are not wireline seated. You can however run wireline and recover them if you need to. They are check valves so you can still circulate down , but it stops back flow.

If you run them, be sure to keep the dart in a clean well oiled condition ready to go, and look after the elastomer, nothing worse then a rusted up dart when you really need it.

При чем же здесь тогда hydraulic?