The O-ring made of rubber protrudes from the opening of the groove and breaks when the operating pressure increases, and this becomes a factor for leakage.

Currently, polytetrafluoroethylene is widely used for the material of the back-up ring.
The shape and dimensional examples when using a back-up ring are shown below.

 

Shape and dimension (JIS unit mm) of a back-up ring made of polytetrafluoroethylene for O-ring

O-ring		Spiral				Bias cut and endless (2)(3)
Standard	Bearing No.	Width （Ｗ）		Thickness （Ｔ）	Opening （Ｚ）（1）	Internal diameter （ｄ）		Outer diameter （Ｄ）		Thickness （Ｔ）
JIS B 2401	P3 ～P10	1.5	+0.03 -0.06	0.7±0.05	1.2±0.4	ｄ	＋0.15 0	D	0 -0.15	1.25±0.1
〃	P10A  ～P22	2.0	+0.03 -0.06	0.7±0.05	1.4±0.8	ｄ	＋0.15 0	D	0 -0.15	1.25±0.1
〃	P22A  ～P50	3.0	+0.03 -0.06	0.7±0.05	2.5±1.5	ｄ	＋0.20 0	D	0 -0.20	1.25±0.1
〃	P48A ～P150	5.0	+0.03 -0.06	0.9±0.06	4.5±1.5	ｄ	＋0.25 0	D	0 -0.25	1.9±0.13
〃	P150A～P400	7.5	+0.03 -0.06	1.4±0.08	6.0±2.0	ｄ	＋0.30 0	D	0 -0.30	2.75±0.15
〃	G25  ～G145	2.5	+0.03 -0.06	0.7±0.05	4.5±1.5
〃	G150～G300	5.0	+0.03 -0.06	0.9±0.06	6.0±2.0
〃	G25   ～G50					ｄ	＋0.20 0	D	0 -0.20	1.25±0.1
〃	G55  ～G145					ｄ	＋0.25 0	D	0 -0.25	1.25±0.1
〃	G150～G300					ｄ	＋0.30 0	D	0 -0.30	1.9±0.13

Note: (1) Z should be the opening when mounted to the shaft of (the standard dimensions of the shaft diameter)
(2) The dimensions for the bias cut and endless represent the dimensions for endless. In bias cut, cutting is performed endlessly.
(3) For bias cut and endless, the difference between the MAX and MIN values of W within one unit must not exceed 0.05mm.

Additionally, when using a back-up ring made of polytetrafluoroethylene, the following points must be noted with particular caution.

・ Spiral: 34.3MPa {350 kgf/cm2} or less
・ Bias and endless (single): 49MPa {500 kgf/cm2} or less ・ Bias and endless (containing filler): 49 to 196MPa {500 to 2000 kgf/cm2}

Back-up ring made of polytetrafluoroethylene (for AN6227, AN6230)　　　　　unit：mm

O-ring		Thickness （Ｔ）	Width （Ｗ）	Opening （Ｚ）（１）
Standard	Bearing No.
A N 6227	1～  7	0.64～0.73	1.38～1.42	0.82～1.57
	8～14		2.21～2.26	0.82～1.98
	15～27		3.05～3.09	1.20～2.36
	28～40	0.79～0.91	4.68～4.72	1.58～4.77
	41～52			2.37～6.35
	53～58	1.17～1.32	6.02～6.07	4.78～7.92
A N 6230	1～25	0.64～0.73	3.02～0.07	2.36～6.35

Back-up ring made of polytetrafluoroethylene (for AN6227, AN6230)