All seals fail… eventually.
Not something you want to hear? But it’s true. At least I am not aware otherwise. Now
eventually can be a really long time – hopefully. It can also be way too short. That’s where the headaches begin. When a seal fails we instinctively blame a bad seal, right? But let’s do a quick refresher on one of the factors that can cause your leak; WEAR.
This is a factor most seen in dynamic applications. Moving parts, varying pressures, fluid and gasses moving through; things just wear out. But how do we control when, or how long before they wear out?
The Parker Fluid Power Guide cites 10 factors that can lead to seal wear.
How many can you name?
Here’s five of the most well known:
2. High pressure
3. High temperature
4. A rough surface finish
5. Media compatibility
When you rule those out, what else is going on?
6. Extra smooth surface can cause premature wear. Too smooth means little lubrication which increases friction that creates heat that can cause accelerated wear that can fail the seal.
7. Speaking of friction, are all the mating parts playing nicely together when it comes to the coefficient of friction? A high coefficient of friction on the material will create higher friction between parts which increases abrasion, heat, and accelerates wear.
8. Ever look at the tensile strength of the seal material? Bubble gum has a low tensile strength. It might have worked on you bike tire for a few blocks when you were a kid (yes, I remember doing that once) but it has no tensile strength and doesn’t last long. Higher tensile strengths help resist abrasion and tearing.
9. Does the fluid have lubricity value? Water isn’t a good lubricant. In dynamic applications sealing water, material selection is important. Is there lubrication at the sealing contact point? What kind? How effective. If not, guess what increased abrasion, friction, temperature etc…
10. Finally, too hard a sealing surface can be a problem. Why? Over time there is usually some ‘smoothing’ of the surfaces where the seal and wear rings contact. If the mating surfaces don’t smooth out, the seals will, causing accelerated wear.
“Wear” is just one family of causes to why seals can fail. The more you know about all the factors and how to combat them the more likely to have a seal that eventually fails… much later.