First, the classification of elbows: 1. The elbow is divided according to its radius of curvature and can be divided into a long radius elbow and a short radius elbow. The radius of curvature of the long radius elbow is equal to 1.5 times the outer diameter of the tube, ie R = 1.5D. The radius of curvature of the short radius elbow is equal to the outer diameter of the tube, ie R=D. Where D is the diameter of the elbow and R is the radius of curvature. 2. If there are about 17 kinds according to the pressure level, they are the same as the American pipe standards: Sch5s, Sch10s, Sch10, Sch20, Sch30, Sch40s, STD, Sch40, Sch60, Sch80s, XS; Sch80, Sch100, Sch120, Sch140, Sch160, XXS, the most commonly used are STD and XS. 3. According to the angle of the elbow, there are 45 degree elbows, 90 degree elbows and 180 degree elbows. In this way, there are many types of elbows. Generally, the following methods are used: "LR STD 90 degrees 8", which means long radius, pressure level is STD, 90 degree 8" elbow; another example, "SR XS 45o 4" means a short radius, a pressure rating of XS, a 45" 4" elbow. Second, the elbow connection method There are two ways to connect the elbow, one is [live connection], and the other is [fixed] (or called [dead connection]) [Live]: (also called detachable connection), is connected by thread. [Fixed]: (also called non-removable connection), is connected by welding. There is a welding method of the welding sleeve. Third, the national standard, the American standard elbow size Inch nominal diameter DN center to end center to center back to end 45o90o180o Center high H center high FPK Long radius long radius short radius long radius short radius long radius short radius 1/2"151638 76 48 3/4"201638 76 51 1"2516382576515641 11/4" 3220483295647052 11/2"40245738114768362 2"5032765115210210681 21/2"65409564191127132100 3"804711476229152159121 31/2"905513389267178184140 4"10063152102305203210159 5"12579190127381254262197 6"15095229152457305313237 8"200126305203610406414313 10"250158381254762508518391 12"300189457305914610619467 14"3502215333561067711711533 16"4002536104061219813813610 18"4502846864571372914914686 20"500316762508152410161016762 22"550347838.2559167611181118838 24"600379914.4610182912191219914 26"650410990.6660 28"7004421066.8711 30"7504731143762 32"8005051219.2813 34"8505371295.4864 36"9005681371.6914 38"9506001447.8965 40"100063115241016 42"10506631600.21067 44"11006941676.41118 46"11507261752.61168 48"12007581828.81219 52"130082119811321 56"140088321341420 60"150094722861524 64"1600101024381620 68"1700107325911727 72"1800113727431829 76"1900119928961930 80"2000126330482032 Inner Support Fabric Air Duct,Air Duct Material,Fabric Air Duct,Air Conditioning System Jiangsu Buna Technology Development Co. , Ltd. , https://www.bunaduct.com