This contoured backup ring is made of Buna-N (also called Nitrile or NBR), has a durometer of 90A, and is designed for use in a wide variety of sealing applications.
Backup 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. Depending upon the direction of pressure in the sealing application, you can either use 1 backup ring or 2 backup rings. If unsure, it is always best to use two backup rings per 1 O-ring.
Buna-nitrile can have high tensile strength, resistance to abrasion, tear, and compression set resistance. It is acceptable for temperature applications between -30 degrees F (-34 degrees C) to 250 degrees F (121 degrees C). It is compatible for use with petroleum, HFA, HFB, and HFC fluids, vegetable oil, alcohol, acids, and aliphatic hydrocarbons. Buna-nitrile is vulnerable to acetone, ethers, esters, ozone, sunlight, and weathering, and should therefore not be used in ozone-generating electric motors, welding equipment, or in applications with exposure to UV light.
The durometer hardness of this Buna backup ring is 90A. Durometers measure the hardness of a material and its resistance to permanent indentation. A higher durometer value indicates greater resistance to indentation. On a scale of 0 to 100, a value of 0 indicates that a sample was completely penetrated, while a value of 100 shows no indentation in the sample. The letter following the number identifies the shore scale, which is either shore A or D. Shore A is used for rubber while shore D is used for harder plastics.