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Compare this product Remove from comparison tool. O-ring seal. O-ring seal circular fluoroelastomer synthetic. O-ring seal circular round polyurethane. PTFE gasket compression. PTFE gasket. See the other products Fama S. O-ring seal with circular cross section round rubber. O-ring seal circular round U-shaped. O-ring seal circular graphite compression.
O-ring gasket series spiral metal compression. O-ring gasket. See the other products Parker Chomerics Division. Excessive heat. In valve applications, the most direct source of heat is from the fluid being sealed. However, some valves may be soaked in heat from the surrounding environment. Pumps, mixers and other high-speed rotary equipment generate frictional heat between the rotating shaft and the static seal.
Chemical attack. Synthetic and vegetable fiber packings can be chemically attacked by fluids at either end of the pH spectrum. Strong acids and bases may cause damage ranging from weakening of the fibers to complete disintegration of the packing material. If the packing is made from several different ingredients, a strong acid or base may selectively attack some ingredients while leaving others untouched. Strong solvents may also attack certain synthetic fibers, or they may dissolve and wash out grease or oil lubricants.
Over time, this may result in a dry packing that does not seal well even under high compressive loading. Strong oxidizers will attack most packing materials with the exception of polytetrafluoroethylene PTFE.
The problem of chemical attack is usually solved by changing to a more resistant seal material. Improper installation. Signs of improper installation can usually be seen upon examination of the failed packing set.
Packing should be cut and installed as individual rings with cut ends that meet after they are twisted around the stem. Packing rings that have bulges in the axial direction are indicative of rings that are either cut too short or too long. This creates gaps or overlaps at each ring and an uneven surface for each successive packing ring and an associated uneven loading of the packing. Each ring should be installed and seated into the bottom of the stuffing box before the next ring is installed.
If rings are not seated properly, this can result in heavy compression of the rings at the top of the set, while the rings deeper in the box are compressed very little. In this case, the packing may be sensitive and hard to control with adjustments. The gland follower should be adjusted evenly so that the packing is not compressed more on one side than the other.
Because the design concept behind a compression packing seal is very simple, one might think that determining the root cause of failure mode might be equally as simple for this type of product.
Unfortunately, this is not the case. Gathering information from others, learning about the seal application, observing the equipment, examining failed seals and becoming familiar with common modes of failure are all tools that can be effective in determining modes of failure and developing corrective action for improved performance.
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Breadcrumbs You are here: Home. Over-tightening, excessive speed and improper installation can cause a system to falter. Garlock Sealing Technologies. In many respects, troubleshooting and failure analysis of packing materials is similar to the investigation of a crime scene. Start by Interviewing Witnesses The troubleshooter should seek information from the people who work with the equipment on a regular basis. Some key questions should be: How is failure defined? Some examples include excessive leakage, overheating, high rate of flush water consumption, excessive friction load and blowout.
Is this application the source of chronic seal failures, or was this an unexpected event? Were there any changes to the seal material, the equipment or the overall process that preceded the failure?
Were there any system upsets or cleaning cycles that preceded the failure? Can you describe the installation procedure? Gather Information About the Victim Knowing the limitations of the sealing product is a key step. S: Size. Is the correct packing cross-section being used? Are the rings cut or formed to the correct length? T: Temperature. A: Application. Some packings are made specifically for rotary equipment while others are intended for valves or static seals.
Check to make sure the packing is suitable for the equipment where it is being used. M: Media. This refers to the fluid being sealed. This seals out the environment. When the door is open. In plastic and metal enclosures, over-compression can happen when a gasket is installed between metal parts that are held together by fasteners.
If an operator over-torques the bolts or screws, the gasket may deform permanently. In other words, the rubber reaches compression set. When the bolts or screws loosen, gaps will form between the metal parts and the gasket material. Applications with temperature changes and vibrations are especially susceptible to the loosening of fasteners. For example, mobile equipment and genset enclosures may be subjected to hot and cold temperatures that cause metal to expand and contract.
Under these dynamic conditions, even fasteners that are torqued properly may loosen. Material relaxation poses gasket-related challenges, too. Enclosure seal failure may not happen but leakage can occur. Rubber profiles that attach to metal surfaces with tape or adhesives are also subject to over-compression. Examples include hatch seals on military vehicles and the dishwasher seals on appliances. Typically, Test Method B is used.
Unlike the other test methods, ASTM D B defines compression set as a percentage of the original deflection — the degree to which a sample of the gasket material is displaced under load. Next, the device and the sample are put in an oven for either 22 or 70 hours depending on the type of elastomer.
The sample is then removed and allowed to cool for 30 minutes before its final thickness is measured. Dynamic stressing also produces compression set, but there are some additional considerations.
Engineers need to know the basics of compression set, but they also need to consider its limitations as a test method.
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