your problem is common when handling latex based media. The comment you found is probably a good enough explanation of the failure mode. The latex is shear sensitive and since, in a single seal application, the media forms the lubricating film between stationary and rotary faces the latex agglomerates and forms a non contiguous layer of hardened latex on the faces. This build up is huge in relation to the normal "sealing gap" of about 1 micron and allows high levels of leakage. There are two answers. One is to use a pressurised double seal where the sealant media is itself the lubricant film between the faces. The downside of that is that a loss of sealant pressure can allow latex into the barrier system and screws up the whole system. Also an unpopular solution with process people in case the inner seal fails and allows dilution/contamination of the media.
The other solution is to go for a knife edged seal. These are usually formed metal bellows seals with tungsten faces one of which is extremely narrow. The principle is not to allow the formation of a fluid film and use very wear resistant faces. The heat generated by high, effectively dry, contact pressure is dissipated by a low pressure water quench on the atmospheric side of the seal (usually less than 0,3 Bar) at a flow rate of around 1/L.Min. You should normally get up to 2 years life with this approach.
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