Definition - What does Hydril mean?
Hydril is a specialized valve which is used to prevent blowout while monitoring, controlling or sealing oil and gas wells. It is one of the types of blowout preventers (BOP's). The annular blowout preventer is known as Hydril, which is named after one of the manufacturers of the device. To shut in the wellbore the hydril uses the principle of wedging.
Petropedia explains Hydril
In onshore or offshore wellhead platforms, the flow of hydrocarbons from drilled wellbore is controlled with the help of the wedge faced piston used by the hydril annular blowout preventer. The advantage of these annular preventers is that they can seal a variety of wellbore and pipe sizes. At the top of BOP stack there is always one hydril annular blowout preventer. For the open holes, elastomric sealing doughnuts are required. This is why they are considered as not so reliable for sealing an open hole in tubulars (or around tubular). The doughnuts used with the Hydril are according to the API specification. These BOP’s are controlled by either electrical, Accoustical control signal, deadman switch or ROV intervention.