How To Classify Rotary Joints

A rotary joint is a connecting sealing device that inputs fluid medium from a stationary pipeline into rotating or reciprocating equipment, and then discharges it from the rotary joint, abbreviated as a "rotary joint".

The application of rotary joints varies and can generally be divided into different types, including hydraulic rotary joints, high-pressure rotary joints, multi-path rotary joints, high-speed rotary joints, high-temperature rotary joints, multi-path rotary joints, central rotary joints, shield machine specific rotary joints, excavator specific rotary joints, machine tool specific rotary joints, etc.

A rotary joint is a sealed connection component that can rotate 360 degrees and transmit media. It has low torque, good sealing performance, long service life, and can be used in conjunction with vacuum emitters.  In general, rotary joints are used for air circulation, and the diameter of the pipeline inside the joint will be the same as the diameter of the external air pipe.  The diameter of the pipeline inside the joint will be 1-2mm larger than that of the external gas pipe. The purpose of this design is to extract the gas inside the equipment completely without leaving any residual gas.

Rotary joints are generally divided into several levels: high-speed, high-pressure, and standard. The main technical parameter difference between these three levels of rotary joints is that the working speed of high-speed rotary joints is generally higher than 1000rpm, the working pressure of high-pressure pneumatic rotary joints is 100kg, while the working speed of standard rotary joints is within 1000rpm, and the working pressure is below 100kg at room temperature.

Rotary joints can be classified according to the medium they pass through: thermal oil rotary joints, water rotary joints, steam rotary joints, hydraulic oil rotary joints, and some rotary joints that pass through special media.

In addition to determining the type of transmission medium, it also depends on the temperature range that can be withstood.  The temperature mainly depends on the material, for example, impregnated phenolic resin graphite material is used below 180 ℃, impregnated furan resin graphite and impregnated white alloy graphite are used below 200 ℃, impregnated bronze graphite and impregnated silver graphite are used below 500 ℃, pure graphite generally does not exceed 500 ℃, and it is best to be below 430 ℃, and bronze is best to be below 300 ℃.

The temperature range of hydraulic rotary joints should not only consider the high temperature they can withstand, but also the low temperature range they can withstand. Low temperature liquid media are mostly saltwater and various liquefied gases. The sealing ring of the rotary joint is made of fluororubber up to -20 ℃ and polytetrafluoroethylene up to -50 ℃. At lower temperatures, metal sealing rings and metal corrugated pipes can be used for sealing, just like in high temperature situations.