Technical Knowledge

A pump running two different fluids does not automatically mean a seal change. The seal only meets the process at a short list of wetted parts: faces, elastomer, and metal hardware. Compatibility is judged part by part. The elastomer is the usual weak point, since SiC, tungsten carbide, and 316 hardware resist most chemicals that destroy rubber. When both fluids fall inside the same material envelope, the seal stays. When one fluid leaves that envelope, the elastomer or the whole seal changes. Temperature follows the hotter service, and residual fluid left in the stuffing box can react with the next fluid, so a chamber flush between services matters. A double seal shifts the question to the barrier fluid.

A removed mechanical seal that smells burnt has overheated at the faces. The smell comes from the elastomer, not the metal. Heat is generated by friction between the rotating and stationary faces once the lubricating fluid film is lost. The three usual causes are dry running, flush system failure, and installation error. A blue or rainbow tint on the carbon face signals oxidation. Diagnosis starts with the faces, then picks the elastomer by the temperature the faces actually reach, not the nameplate figure.

A mechanical seal's metal parts, the sleeve, gland and springs, ship as 316 stainless by default. See the rule for when upgrading to duplex 2205 pays on a rebuild, when 316 stays the call, and why the spring often needs a better alloy than the sleeve.

A mechanical seal cross-section is read from the centreline outward. Learn which face turns, where the sealing film sits, how balance ratio and spring layout read on the drawing, and what each part does before the order goes in.

A discontinued pump still needs a seal that fits. See what to measure, the three ways to source a replacement, and when to match the old seal or convert to a cartridge.