A door closer pivoted on a door at least includes a case and a piston. When the door is open, the door closer blocks a communicating hole of the case by an oil sealing ring of the piston to allow an oil filled in the door closer cannot flow through the communicating hole. As a result, the open door can be held in a predetermined position.

The present invention relates to novel lignin-derived compounds and compositions comprising the same and their use as redox flow battery electrolytes. The invention further provides a method for preparing said compounds and compositions as well as a redox flow battery comprising said compounds and compositions. Additionally, an assembly for carrying out the inventive method is provided.

A door closer including: a body defining a chamber therein; a piston slidably supported within the chamber, and dividing the chamber into first and second cavities either side of the piston, which in use receive liquid; a biasing device for biasing the piston towards the first cavity; a passageway connecting the first cavity to the second cavity for permitting the flow of fluid therebetween; a blocking member for controlling the flow of liquid through the passageway between the cavities; a moveable member moveable between first and second positions, wherein when the moveable member is in its first position the moveable member causes or permits the blocking member to assume a blocking position, thus preventing or at least inhibiting the flow of liquid from the first to the second cavity, and wherein when the moveable member is in its second position the moveable member causes or permits the blocking member to assume a non-blocking position, thus permitting the flow of liquid from the first to the second cavity; and a permanent magnet positioned adjacent or close to the moveable member for holding the moveable member in its first position; wherein the door closer includes a pole switching device that can produce a magnetic field that is in opposition to the magnetic field of the permanent magnet to effectively cancel out or overcome the magnetic field of the permanent magnet and produce a net magnetic field that is either zero or in the opposite direction to the magnetic field of the permanent magnet so as to effect movement of the moveable member between its first and second positions.

A power-assist device (1) with a piston rod (8), which is mounted movably in a housing (7) and has a first position and a second position, and with a preferably elastic return element (12), which can be arrested by a positionally variable arresting part (10) and which, in the unlocked state, can transmit an assisting force to the piston rod (8) and, in the arrested state, is decoupled in terms of force from the piston rod (8), such that, in the unlocked state, as a result of the piston rod (8) being moved into the first position, the arresting part (10) is moved out of an unlocking position into an arresting position, which enables arresting of the restoring return (12) only within a limited time period.