Mechanical Seals come in a wide range of designs however the most important factor when determining how long a seal is going to last, is deciding on the right seal face materials. The old adage "pay me now or pay me later" applies to seals. You must consider the environment the seal will be exposed to. Abrasive environments require seal faces that will hold up to the wear and tear of abrasive environments. It makes little sense to save money on the seal only to have to spend more money to replace the seal later. On the other hand if you are pumping very clean fluid that has a lubricating quality such as machine oil or Ethylene Glycol, save your money for better quality bearings.