A like for like replacement is only like for like if the material, design and operating duty are still the same. A seal can have the same dimensions and still use a different elastomer grade, cure system or face material. The plant may also have changed its cleaning cycle, product, speed or operating temperature without changing the old seal specification.
Before fitting a third seal, keep the failed parts and look at where the leak started. Check the faces and the secondary seals separately. Compare the old and new part numbers and compound documents. Then record the actual product, CIP chemicals, steam cycle, pressure, temperature and starts. If the seal faces show heat damage, also check whether the pump has lost liquid at the faces or the flush has stopped. If the elastomer is swollen or has lost its squeeze, look at the compound and duty first.
I would not move straight to the most expensive material. Find what changed, then specify the complete seal for the current duty. The old drawing is a starting point, not proof that the old choice is still right.
Andrew Sykes | Acumen Seals & Pumps Limited | Independent mechanical seals and sealing specialist