How do ester's condition seals

[RB Shannon]

I pretty much understand polarity of molecules and solvency,but what reaction takes place for a PAO to shrink a seal and an ester to condition or soften a seal back up, or what causes incompatabilty between seal material and affluent's for that matter??

 

[MolaKule]

Since PAO has little solvency and is basically non-polar, it doesn't react at all with seal elastomers. So PAO's "allow" seals to harden by their "non-reactive" or "inertness" qualities.

Mineral ois with their sulfur polarity, do cause seals to swell slightly. When all PAO fluids were introduced, someone forgot about the natural seal swell tendency of mineral oils and why they did not leak as badly as with the all new PAO's. Initially, PAO's were mixed with mineral oils as an additive to lower pour point, reduce friction, and increase oxidation stability. Of course, seals did not leak with these "blends."

Any highly polar molecule such as ester actually substitutes itself into the elastomer, resulting in an increase in the number of hydrocarbon molecules, causing the seals to swell.

[ February 24, 2003, 01:13 AM: Message edited by: MolaKule ]

 

[RB Shannon]

Thanks

that makes sense,so the density of the elastomer would be a critical factor in determining fluid compatabity( or how much it can absorb), or am I off base

 

[Al]

Yes-great info Molakule,
Thanks

 

[MolaKule]

RB,

"...so the density of the elastomer would be a critical factor in determining fluid compatabity( or how much it can absorb), or am I off base"

Bot density and the type of elastomer (synthetic rubber) and its molecular structure would be important in determining a fluid's compatibility.