8am-4pm Pacific Mon-Fri | 208-413-6377

Back-Up Ring Size

Back-Up rings are used for both static and dynamic fluid power applications and prevent the migration or extrusion of an O-Ring in the gap as pressurization and de-pressurization/pressure cycling occur. The profile shape of the Back-Up rings is usually rectangular but may also be concave at the face mating with the O-Ring. Manufactured in various PTFE compounds, Buna-N 90 Durometer, FKM 90 Duro, thermoplastic polyester elastomer TPE ((Hytrel®) or less common urethane Back-Up Rings.

Extrusion failure is one of the most common types of O-Ring failure. When the internal pressure of an application becomes too great, the O-Ring will actually extrude into the clearance gap. This extrudate will quickly be nibbled away causing a loss of material, and once sufficient material is lost, seal failure will quickly follow. There are three options to prevent this, the first of which is to reduce the clearances to lower the extrusion gap. This is obviously an expensive option, so a cheaper solution is to raise the durometer of the O-Ring. Even though a higher durometer O-Ring offers superior extrusion resistance, this is often not a feasible solution due to material availability, and to the fact that harder durometer materials have limited low pressure sealing ability. The last and best option is the addition of a Back-Up ring. A Back-Up ring is a ring of hard, extrusion resistant material such as high durometer Buna Nitrile, FKM Flourocarbon, TPE or PTFE. In a sealing application, Back-Up rings provide added extrusion resistance, and prevent damage to O-Rings and seals when subjected to high pressures, larger extrusion gaps, and/or high temperatures.

A Back-Up ring is designed to fit between the O-Ring and the extrusion gap and prevent the extrusion of the O-Ring. Depending upon the direction of pressure in the sealing application, you can either use 1 Back-Up ring or 2 Back-Up rings. If unsure, it is always best to use two Back-Up rings per 1 O-Ring.

 O-Ring Back-Up Rings Design for Higher Pressure Applications

  • Back-Up Rings used with O-Rings at pressures > 1500 psi or big extrusion gaps
  • Back-Up Rings are designed to limit O-Ring clearance gap extrusion.
  • Available in elastomeric compounds, TPE and PTFE Back-Up Rings.
  • PTFE Back-up rings can be solid, split, spiral, or custom for ease of install.
  • PTFE Back-up Ring size standards AN6244, AN6246, MS27595, MS28774, MS28782 and MS28783.
  • Elastomer Back-up Rings are typically contoured to conform to an O-Ring.
  • Elastomer Back-up Rings fit standard USA and custom O-Ring sizes.
  • Back-up Rings require wider glands to accommodate.

Back Up Rings are flat, split, spiral or contoured washer type fittings used to protect an O-Ring seal from extrusion at higher pressures and temperatures. A Back Up Ring works by blocking or reducing the extrusion gap, thus preventing the O-Ring from extruding. The use of a back-up ring increases the pressure and temperature capability of O-Rings. Back Up Rings can be solid, split, spiral or contoured. The split and spiral back-up rings are easier to install, especially in small diameters. The chart to the right depicts the higher pressure capabilities of using Back Up Rings for a given clearance gap dimension. Back Up Rings can be used on both sides of the O-Ring if pressure is bidirectional. Gland widths should be widened to accommodate one or two Back Up Rings.

Elastomeric Contoured back-ups are routinely produced in a 90 durometer Buna Nitrile and FKM. This provides sufficient elasticity to permit stretching over the major diameter of a piston and then snapping back into the gland groove cut into the piston. 90 durometer has sufficient hardness to resist extrusion of the softer elastomeric O-Ring performing the actual sealing function against the high pressure liquid or gas.

  • -000 Series O-Rings 0.070" ±0.003" - .045" Thick
  • -100 Series O-Rings 0.103" ±0.003" - .045" Thick
  • -200 Series O-Rings 0.139" ±0.004" - .040" Thick
  • -300 Series O-Rings 0.210" ±0.005" - .060" Thick
  • -400 Series O-Rings 0.275" ±0.006" - .096" Thick

   

Rubber Contoured Back-Up Ring Size Chart

Links to order the following:
Buna-N 90 Dished Back-upsTPE Back-Up Rings (Hytrel®)FKM Dished Back-upsTeflon SolidTeflon SplitBack-up Kits

SIZE ID +/- R* T** A +/- W +/-
-004 0.096 0.005 0.087 0.049 0.045 0.003 0.053 0.003
-005 0.127 0.005 0.087 0.049 0.045 0.003 0.053 0.003
-006 0.140 0.005 0.087 0.049 0.045 0.003 0.053 0.003
-007 0.171 0.005 0.087 0.049 0.045 0.003 0.053 0.003
-008 0.202 0.005 0.087 0.049 0.045 0.003 0.053 0.003
-009 0.234 0.005 0.087 0.049 0.045 0.003 0.053 0.003
-010 0.265 0.005 0.087 0.049 0.045 0.003 0.053 0.003
-011 0.327 0.005 0.087 0.049 0.045 0.003 0.053 0.003
-012 0.390 0.005 0.087 0.049 0.045 0.003 0.053 0.003
-013 0.455 0.005 0.087 0.049 0.045 0.003 0.053 0.003
-014 0.518 0.005 0.087 0.049 0.045 0.003 0.053 0.003
-015 0.580 0.007 0.087 0.049 0.045 0.003 0.053 0.003
-016 0.643 0.009 0.087 0.049 0.045 0.003 0.053 0.003
-017 0.705 0.009 0.087 0.049 0.045 0.003 0.053 0.003
-018 0.768 0.009 0.087 0.049 0.045 0.003 0.053 0.003
-019 0.830 0.009 0.087 0.049 0.045 0.003 0.053 0.003
-020 0.893 0.009 0.087 0.049 0.045 0.003 0.053 0.003
-021 0.955 0.009 0.087 0.049 0.045 0.003 0.053 0.003
-022 1.018 0.010 0.087 0.049 0.045 0.003 0.053 0.003
-023 1.080 0.010 0.087 0.049 0.045 0.003 0.053 0.003
-024 1.143 0.010 0.087 0.049 0.045 0.003 0.053 0.003
-025 1.205 0.011 0.087 0.049 0.045 0.003 0.053 0.003
-026 1.268 0.011 0.087 0.049 0.045 0.003 0.053 0.003
-027 1.330 0.011 0.087 0.049 0.045 0.003 0.053 0.003
-028 1.393 0.013 0.087 0.049 0.045 0.003 0.053 0.003
-029 1.518 0.013 0.087 0.049 0.045 0.003 0.053 0.003
-030 1.643 0.013 0.087 0.049 0.045 0.003 0.053 0.003
-031 1.768 0.015 0.087 0.049 0.045 0.003 0.053 0.003
-032 1.893 0.015 0.087 0.049 0.045 0.003 0.053 0.003
-033 2.018 0.018 0.087 0.049 0.045 0.003 0.053 0.003
-034 2.143 0.018 0.087 0.049 0.045 0.003 0.053 0.003
-035 2.268 0.018 0.087 0.049 0.045 0.003 0.053 0.003
-036 2.393 0.018 0.087 0.049 0.045 0.003 0.053 0.003
-037 2.518 0.018 0.087 0.049 0.045 0.003 0.053 0.003
-038 2.643 0.020 0.087 0.049 0.045 0.003 0.053 0.003
-039 2.768 0.020 0.087 0.049 0.045 0.003 0.053 0.003
-040 2.893 0.020 0.087 0.049 0.045 0.003 0.053 0.003
-041 3.018 0.024 0.087 0.049 0.045 0.003 0.053 0.003
-042 3.268 0.024 0.087 0.049 0.045 0.003 0.053 0.003
-043 3.518 0.024 0.087 0.049 0.045 0.003 0.053 0.003
-044 3.768 0.027 0.087 0.049 0.045 0.003 0.053 0.003
-045 4.018 0.027 0.087 0.049 0.045 0.003 0.053 0.003
-046 4.268 0.030 0.087 0.049 0.045 0.003 0.053 0.003
-047 4.518 0.030 0.087 0.049 0.045 0.003 0.053 0.003
-048 4.768 0.030 0.087 0.049 0.045 0.003 0.053 0.003
-049 5.018 0.037 0.087 0.049 0.045 0.003 0.053 0.003
-050 5.268 0.037 0.087 0.049 0.045 0.003 0.053 0.003
-102 0.077 0.005 0.129 0.053 0.045 0.003 0.086 0.003
-103 0.109 0.005 0.129 0.053 0.045 0.003 0.086 0.003
-104 0.140 0.005 0.129 0.053 0.045 0.003 0.086 0.003
-105 0.171 0.005 0.129 0.053 0.045 0.003 0.086 0.003
-106 0.202 0.005 0.129 0.053 0.045 0.003 0.086 0.003
-107 0.234 0.005 0.129 0.053 0.045 0.003 0.086 0.003
-108 0.265 0.005 0.129 0.053 0.045 0.003 0.086 0.003
-109 0.327 0.005 0.129 0.053 0.045 0.003 0.086 0.003
-110 0.390 0.005 0.129 0.053 0.045 0.003 0.086 0.003
-111 0.452 0.005 0.129 0.053 0.045 0.003 0.086 0.003
-112 0.515 0.005 0.129 0.053 0.045 0.003 0.086 0.003
-113 0.577 0.007 0.129 0.053 0.045 0.003 0.086 0.003
-114 0.640 0.009 0.129 0.053 0.045 0.003 0.086 0.003
-115 0.702 0.009 0.129 0.053 0.045 0.003 0.086 0.003
-116 0.765 0.009 0.129 0.053 0.045 0.003 0.086 0.003
-117 0.831 0.010 0.129 0.053 0.045 0.003 0.086 0.003
-118 0.893 0.010 0.129 0.053 0.045 0.003 0.086 0.003
-119 0.956 0.010 0.129 0.053 0.045 0.003 0.086 0.003
-120 1.018 0.010 0.129 0.053 0.045 0.003 0.086 0.003
-121 1.081 0.010 0.129 0.053 0.045 0.003 0.086 0.003
-122 1.143 0.010 0.129 0.053 0.045 0.003 0.086 0.003
-123 1.206 0.012 0.129 0.053 0.045 0.003 0.086 0.003
-124 1.268 0.012 0.129 0.053 0.045 0.003 0.086 0.003
-125 1.331 0.012 0.129 0.053 0.045 0.003 0.086 0.003
-126 1.393 0.012 0.129 0.053 0.045 0.003 0.086 0.003
-127 1.456 0.012 0.129 0.053 0.045 0.003 0.086 0.003
-128 1.518 0.012 0.129 0.053 0.045 0.003 0.086 0.003
-129 1.581 0.015 0.129 0.053 0.045 0.003 0.086 0.003
-130 1.643 0.015 0.129 0.053 0.045 0.003 0.086 0.003
-131 1.706 0.015 0.129 0.053 0.045 0.003 0.086 0.003
-132 1.768 0.015 0.129 0.053 0.045 0.003 0.086 0.003
-133 1.831 0.015 0.129 0.053 0.045 0.003 0.086 0.003
-134 1.893 0.015 0.129 0.053 0.045 0.003 0.086 0.003
-135 1.956 0.017 0.129 0.053 0.045 0.003 0.086 0.003
-136 2.018 0.017 0.129 0.053 0.045 0.003 0.086 0.003
-137 2.081 0.017 0.129 0.053 0.045 0.003 0.086 0.003
-138 2.143 0.017 0.129 0.053 0.045 0.003 0.086 0.003
-139 2.206 0.017 0.129 0.053 0.045 0.003 0.086 0.003
-140 2.268 0.017 0.129 0.053 0.045 0.003 0.086 0.003
-141 2.331 0.020 0.129 0.053 0.045 0.003 0.086 0.003
-142 2.393 0.020 0.129 0.053 0.045 0.003 0.086 0.003
-143 2.456 0.020 0.129 0.053 0.045 0.003 0.086 0.003
-144 2.518 0.020 0.129 0.053 0.045 0.003 0.086 0.003
-145 2.581 0.020 0.129 0.053 0.045 0.003 0.086 0.003
-146 2.643 0.020 0.129 0.053 0.045 0.003 0.086 0.003
-147 2.706 0.022 0.129 0.053 0.045 0.003 0.086 0.003
-148 2.768 0.022 0.129 0.053 0.045 0.003 0.086 0.003
-149 2.831 0.022 0.129 0.053 0.045 0.003 0.086 0.003
-150 2.893 0.022 0.129 0.053 0.045 0.003 0.086 0.003
-151 3.018 0.024 0.129 0.053 0.045 0.003 0.086 0.003
-152 3.268 0.024 0.129 0.053 0.045 0.003 0.086 0.003
-153 3.518 0.024 0.129 0.053 0.045 0.003 0.086 0.003
-154 3.768 0.028 0.129 0.053 0.045 0.003 0.086 0.003
-155 4.018 0.028 0.129 0.053 0.045 0.003 0.086 0.003
-156 4.268 0.030 0.129 0.053 0.045 0.003 0.086 0.003
-157 4.518 0.030 0.129 0.053 0.045 0.003 0.086 0.003
-158 4.768 0.030 0.129 0.053 0.045 0.003 0.086 0.003
-159 5.018 0.035 0.129 0.053 0.045 0.003 0.086 0.003
-160 5.268 0.035 0.129 0.053 0.045 0.003 0.086 0.003
-161 5.518 0.035 0.129 0.053 0.045 0.003 0.086 0.003
-162 5.768 0.035 0.129 0.053 0.045 0.003 0.086 0.003
-163 6.018 0.035 0.129 0.053 0.045 0.003 0.086 0.003
-164 6.268 0.040 0.129 0.053 0.045 0.003 0.086 0.003
-165 6.518 0.040 0.129 0.053 0.045 0.003 0.086 0.003
-166 6.768 0.040 0.129 0.053 0.045 0.003 0.086 0.003
-167 7.018 0.040 0.129 0.053 0.045 0.003 0.086 0.003
-168 7.268 0.045 0.129 0.053 0.045 0.003 0.086 0.003
-169 7.518 0.045 0.129 0.053 0.045 0.003 0.086 0.003
-170 7.768 0.045 0.129 0.053 0.045 0.003 0.086 0.003
-171 8.018 0.045 0.129 0.053 0.045 0.003 0.086 0.003
-172 8.268 0.050 0.129 0.053 0.045 0.003 0.086 0.003
-173 8.518 0.050 0.129 0.053 0.045 0.003 0.086 0.003
-174 8.768 0.050 0.129 0.053 0.045 0.003 0.086 0.003
-175 9.018 0.050 0.129 0.053 0.045 0.003 0.086 0.003
-176 9.268 0.055 0.129 0.053 0.045 0.003 0.086 0.003
-177 9.518 0.055 0.129 0.053 0.045 0.003 0.086 0.003
-178 9.768 0.055 0.129 0.053 0.045 0.003 0.086 0.003
-201 0.202 0.005 0.174 0.050 0.040 0.003 0.118 0.004
-202 0.265 0.005 0.174 0.050 0.040 0.003 0.118 0.004
-203 0.327 0.005 0.174 0.050 0.040 0.003 0.118 0.004
-204 0.390 0.005 0.174 0.050 0.040 0.003 0.118 0.004
-205 0.455 0.005 0.174 0.050 0.040 0.003 0.118 0.004
-206 0.