Flange, also known as a flange disc or boss, is a component used for connecting shafts or for joining pipe ends. It is also used at equipment inlets and outlets, such as reducer flanges, for connecting two pieces of equipment. A flange connection or flange joint refers to a removable connection made up of a flange, a gasket, and bolts, forming a combination seal structure. Pipe flanges are the flanges used in piping installations, and when used on equipment, they refer to the equipment's inlet and outlet flanges. Flanges have holes, and bolts secure them tightly. They are sealed with a gasket. Flanges come in threaded (screwed) connections,焊接 (welded) flanges, and clamp flanges. Flanges are always used in pairs; low-pressure pipelines can use threaded flanges, while those above 4 kg pressure use焊接 flanges. A sealant is placed between the two flange disks, and then bolts are tightened. Flanges of different pressures have different thicknesses and require different bolts. Pumps and valves, when connected to pipelines, have corresponding flange shapes for the equipment, also known as flange connections. Any connection piece that uses bolts to connect two flat surfaces around the perimeter and is sealed is generally called a "flange," such as the connection of ventilation pipes. Such components can be referred to as "flange-type parts." However, this type of connection is only a part of a single device, like the connection between a flange and a pump, so it's not appropriate to call the pump a "flange-type part." Smaller components like valves can be called "flange-type parts."