Wave Spring Mechanical Seals: Principally used for liquids of high viscosity, wave spring mechanical seals are popular for pharmaceutical, dairy, brewery and food processing applications. They are often fitted to the shaft with grub screws and in the case of high viscosity media would also have stationaries with anti-rotation pins. Some designs are specially constructed to work in shallow, confined seal housings. http://www.egerseal.com/mechanical-seal/elastomer-bellows-seals/