Seal life is determined by a wide variety of factors, many of which are independent of the actual seal design. Installation issues, improper pump operation, and an inadequate seal support system are just a few. Very close attention must be paid to the selection of a mechanical seal and its components—including faces, O-rings, and metallurgy—to ensure maximum life. It’s also critical that the appropriate seal type is chosen for each different application and that the installation procedure is accurately followed. Two of the most common seal failure causes are heat generation and improper installation, both of which have multiple potential root causes.
Prevent Heat Generation from Decreasing Mechanical Seal Life
Today, one of the most commonly used seal face combinations is a softer carbon face against a much harder silicon carbide face. This is a cool-running combination if there is no seal support system, such as a flush plan, in place. Excess heat generation between seal faces will drastically reduce seal life, and must be avoided. The softer carbon face against a silicon carbide face does not generate nearly as much heat as other face combinations, and is therefore a good option for seals without seal support systems.
Seal support systems, such as a plan 11 (flush line from pump discharge), a plan 13 (recirculation to pump suction), or a Plan 53A (pressurized barrier fluid with a seal reservoir), can be simple or highly complex, but they all have the same goal: to keep the seal faces clean, cool, and well-lubricated. If there is a seal support system and abrasives are present, changing the carbon face to either Silicon Carbide or a Tungsten Carbide face is a much better option for extending seal life, as the two hard silicon faces will be much more resistant to abrasion. The piping plan will compensate for the excess heat generated by the two hard faces, increasing seal life. If there are no abrasive solids and there is no chemical issue with the process fluid, then the Carbon versus Silicon Carbide face is the best seal face combination to use.
Proper Installation Extends the Life of Mechanical Seals
Improper installation of a mechanical seal is another one of the most common causes of failure. Seal installation should be performed in the steps outlined by the manufacturer, and with great care to avoid damaging the delicate seal faces / O-rings. Forgetting to tighten set screws before removing setting clips, not tightening gland bolts evenly, damaging O-rings, nicking seal faces, and piping connection errors are some of the common installation mistakes made when installing a seal.
Component seal installation is inherently more prone to installation errors when compared to cartridge seals due to the extra steps and measurements needed. This is why, if possible, a cartridge seal design should be chosen over a component design. There is already enough to be meticulous about when installing a mechanical seal; why add additional opportunity for installation mistakes?
The correct seal face combinations, proper installation by a trained technician, a seal support piping plan, and good seal selection will lead to longer MTBF, which is what we are all looking for at the end of the day. There is an understandable cost increase for these improvements, but data suggests that the extra cost is well worth it, as replacing a burned-out seal is much more costly in the end.
As our Chief Engineer Kim Simmons always preaches, “A cool seal is a happy seal.”