The basic components of the hydraulic door closer include support guides, transmission gears, return springs, check valves, rack plungers, throttle spools and housings, end caps, seals, and connecting rods. The housing and the connecting rod act as fixed door closers and connect the door leaf and the door frame.The working principle of the door closer is: when the door is opened, the door body drives the link to move, and the transmission gear rotates to drive the rack plunger to the right. The spring is compressed during the right shift of the plunger and the hydraulic oil in the right chamber is also pressurized. The one-way valve ball on the left side of the plunger is opened under the action of oil pressure, and the hydraulic oil in the right chamber flows through the one-way valve into the left chamber. When the door opening process is completed, since the spring is compressed during the opening process, the accumulated elastic potential energy is released, pushing the plunger to the left side, and driving the transmission gear and the door closer link to rotate, so that the door is closed.During the release of the spring, since the hydraulic oil in the left chamber of the door closer is compressed, the check valve is closed, and the hydraulic oil can only flow out through the gap between the housing and the plunger, and passes through the small hole in the plunger and 2 The flow path with the throttle spool is returned to the right chamber. Therefore, the hydraulic oil forms a resistance to the release of the spring, that is, the damping effect is achieved by the throttling, and the speed at which the door is closed is controlled. The throttle valve on the valve body can be adjusted to control the variable closing speed of different stroke segments. Although the structure and size of the door closers produced by different manufacturers are different, the principle is the same.The types of door closers can be divided into: exterior and in-line door closers, in-door door closers, door bottom door closers ( floor springs), vertical door closers (built-in Vertical door closers) and other types of door closers.