Briton 121 door closer

Briton Door Closer - eBay
Briton121CE Fire DoorCloser. Suitable for 2 hour fire doors, included in EN1634 fire test. Successfully tested to EN1154 & fully CE marked in regular and transom mounted positions.

How to Adjust Your Door Closer - Dengarden
A doorcloser is a mechanical device designed to close a door slowly but firmly enough to latch. It accomplishes this by using spring tension modulated by hydraulic fluid. As the user opens the door, hydraulic fluid passes from one reservoir to another.