Precautions for using socket-type pipe fittings

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Precautions for using socket tube fittings: Socket tube fittings have advantages such as a simple structure, ease of use, and the elimination of the need for welding. However, in medium and high-pressure hydraulic systems, improper operation often leads to leaks, which hinders their widespread use. Through years of practice, the author has summarized some experiences that have yielded good results. As shown in the attached diagram, the ferrule-type pipe joint mainly consists of three parts: a joint body 1 with a 24-degree conical hole, a ferrule 2 with sharp inner edges, and a compression nut 3 that serves to apply pressure. When nut 3 is tightened, collar 2 is pushed into the 24-degree tapered hole and deforms as a result, enabling spherical contact sealing between the collar and the tapered surface inside the connector body ； At the same time, the inner cutting edge of the sleeve fits into the outer wall of the steel pipe 4, creating an annular groove on that outer wall, thereby providing a reliable sealing effect. It is best to use 20# precision-drawn pipes that have undergone stress-relief annealing; this facilitates the embedding of the inner edge of the collar into the outer surface of the steel pipe, thereby ensuring a reliable seal. (1) Pre-installation ① The pre-installation of cartridge-type pipe fittings is the most crucial step, as it directly affects the reliability of the seal. A dedicated preloader is generally required. Joints with small diameters can be pre-assembled on a vise. The specific method is to use a joint body as the base, and then press the nut and collar onto the pipe. The main types include bayonet-style straight pipe fittings, bayonet-style end straight connectors, and bayonet-style tee pipe fittings. The author found that even for the same batch of products from the same manufacturer, the depth of the conical holes in these different types of connectors often varies, which leads to leaks; yet this issue is often overlooked. The proper approach is to use the same type of fitting at the connection end that corresponds to the fitting used at one end of the pipe, which helps to minimize the risk of leaks. ②The ends of the pipes should be flush. After the pipe is cut, it should be polished smooth using tools such as grinding wheels, burrs should be removed, it should be cleaned and blown clean with high-pressure air before use. ③During pre-installation, efforts should be made to maintain coaxiality between the tube and the fitting; excessive deviation of the tube can also lead to sealing failure. ④The preloading force should not be too large. The inner edge of the collet should fit snugly against the outer wall of the tube, with no noticeable deformation in the collet. When connecting the pipes, assemble them using the specified tightening force. The tightening force for φ6-10mm ferrules is 64-115N, for φ16mm it is 259N, and for φ18mm it is 450N. If the sleeve is severely deformed during pre-installation, it will lose its sealing function. (2) The addition of sealants and other fillers is prohibited. Some people apply sealant to the ferrule in order to achieve a better seal, but as a result the sealant ends up entering the hydraulic system, causing problems such as blockages in the damping holes of the hydraulic components. (3) When connecting the pipelines, ensure that the pipes have sufficient deformation allowance to avoid subjecting them to tensile stress. (4) When connecting the pipelines, avoid subjecting them to lateral forces, as excessive lateral forces can lead to poor sealing. (5) When connecting the pipelines, tighten them all at once to avoid multiple disassemblies, as this can also degrade the sealing performance