When you think about it, the rubber in sealing rings is an amazing material. It is a recent discovery, only introduced in 1736. It was not until 1700 that Joseph Priestley developed rubber in its first commercial use as a pencil eraser. The usefulness of rubber lies in its elasticity, defined as the ability of rubber to deform reversibly under stress. When placed between two highly inelastic pieces of metal, it deforms to form a seal that is highly impervious to liquid or gas passage, even under extreme temperatures and pressures. Thermoplastics are a modern form of elastic sealing material which forms the basis of high-performance profile rings in compressors.
What Makes Profile Rings Fail?
Much like our skin, which is also highly elastic when we are young, thermoplastic material loses its inelasticity with age. This process is sped up in the presence of extreme temperatures or caustic materials. In other words, aged profile rings lose the ability to return to its original form. This reduces its ability to form an effective seal.
Symptoms of a Failing Seal
In many systems, the first symptoms of a failing seal are a visible leak at the seal joint. In a compressor system, the symptoms are less obvious. One of the key symptoms is a loss of pressure. Although this can be attributed to the age or degradation in several parts of the system, the most common point of failure is the system. For this reason, monitoring pressure is an excellent way to determine when profile rings need to be replaced.
Failing rings are not like a flat tire. They do not fail all at once. The effect of their degradation is more like a slow leak. For this reason, the technician who monitors pressure as a means to determine the useful lifetime should have a boundary failure level for pressure, one well in advance of the pressure requirements of the system.
Replace Them All
Thermoplastic failure in a particular system is highly predictable. When one seal begins to fail, the others will soon follow. For this reason, it is a good idea to replace seals at the first sign of degradation, or alternately, on a fixed time schedule.