Seal swelling

Seal swell agent 0.3-1.5% Combats seal embiittlement/cracking due to base oil choice... 

Seal Swell Agents, as sulphurized esters, but which can affect frictional characteristics at high levels,... 

In common with the mineral-based H-515 fluid the PAO-based fluids also contain hindered phenol-based anti-oxidants and TCP as an anti-wear agent but, as previously stated, they do not need the addition of a VI improver [27]. PAOs tend to give very low swell of the elastomer types used in the applicable hydraulic systems. A certain degree of elastomer swell is required to ensure good sealing of the system and therefore the PAO-based fluids contain up to 35% by weight of di-ester to produce sufficient seal swell. 

Dibasic esters are made from carboxylic diacids and alcohols. Adipic acid (hexanedioic acid) is the most commonly used diacid (Figure 5). Because it is linear, adipic acid is usually combined with branched alcohols, such as 2-ethylhexanol or isotridecanols (C13H27OH) to give esters with balanced VI and low temperature properties (Figure 5). Dibasic ester is most often used as a co-base stock with PAO to improve solvency and seal swell properties of the final lubricants. 

Its causes are excessive seal swell, metal-to-metal contact (i.e., out of alignment), seal extrusion, and excessive squeeze. 

Antioxidants Dispersants Detergents Demulsifiers Seal Swell Antifoam... 

Base stock functions that fall into the preservation area include volatility, pour point, solvency, colour, smell, toxicity, and stability against thermal stress, hydrolysis and shear. Biostability or bio-degradability may be required for different applications. Additive functions that fall under preservation include oxidation inhibition, dispersancy, detergency, demulsification, seal swelling, anti-foam and corrosion inhibition. 

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