https://www.ryobi-group.co.jp/en/projects/builder/products/01_d4550_spec.html

 The lower the opening resistance / higher the efficiency
 Accurate production of all product components, based on the original quality control system of
 Ryobi
 Low resistance to door opening by children, the elderly and the disabled
 D-4550 Series Door Closers can be used on both RH and LH doors for both push side and side assemblies.
 Full hydraulic control
 Wind resistance property is defined and adjusted by an independent valve.
 When doors are violently opened by pedestrians or wind, the backcheck feature
 Reduces the likelihood of damage to a wall or an adjacent obstacle.
 For doors laden with public building, schools and colleges this facility protects people and property.
 Optional delayed operation
 Optional delayed action feature adjusted by a standalone valve.
 Once set, the door - when opened 70 degrees enters into a delayed position that allows
 Extra time before closing. The delayed time can be adjusted to change from seconds to minutes
 , Depending on the angle at which the door opens. Delayed closure is an advantage for: nursing staff assisting patients, maintenance staff with strollers, and the elderly or sick walking with sticks or frames under supervision.