What is the difference between threaded connections and flanged connections?

It is recommended to study mechanical design a bit and look into issues related to connections. Threaded connections primarily use sealing threads to prevent leaks. Flange connection achieves sealing through the flange sealing surface and gasket.

Are you asking about pipe threaded connections? Those are usually sealed pipe threads

Threaded connection: This is a simple method of connection, commonly used for small valves. There are also two cases: 1) Direct sealing: the internal and external threads serve as a seal directly. To ensure that the joints do not leak, lead grease, linen rope, and PTFE tape are often used for sealing ； Among them, polytetrafluoroethylene sealing tape is being used more and more widely ； This material has excellent corrosion resistance and superior sealing properties; it is easy to use and store. When removed, it can be taken off completely, as it is a non-stick film, making it far superior to lead paint and hemp rope. 2) Indirect sealing: The force generated by tightening the threads is transmitted to the gasket between the two surfaces, allowing the gasket to perform a sealing function. Flange connection: This is the most commonly used connection type in valves. Based on the shape of the joint surface, it can be further divided into the following types: 1) Smooth type: used for valves with low pressure. It is relatively easy to process. 2) Grooved type: It operates under higher pressure, and medium-hard gaskets can be used. 3) Tenon-and-socket type: Gaskets with greater plastic deformation can be employed; it is widely used in corrosive environments and provides good sealing performance. 4) Trapezoidal groove type: An oval metal ring is used as a washer; it is applied to valves with a working pressure of ≥64 kilograms per square centimeter, or to high-temperature valves. 5) Lens type: The washer is lens-shaped and made of metal. Used for high-pressure valves with a working pressure of ≥100 kilograms per square centimeter, or for high-temperature valves. 6) O-ring type: This is a relatively new type of flange connection that has developed with the advent of various rubber O-rings; it offers more reliable sealing performance compared to ordinary flat gaskets.

It is recommended that the poster check the mechanical manual or look into the principles of mechanics

Threaded connection: low pressure, small pipe diameter, easy to install, prone to leakage. Flange connection: large pipe diameter, high pressure, complex installation, and occupies space.