Back up sealing


The best mechanical seal in the world is going to fail some day. You need back up sealing if:

  • The product you are sealing is dangerous. You’ll need some means of protecting people in the area.
  • The product is costly.
  • The product presents an environmental hazard if any of it leaks into the atmosphere, or on the ground.
  • You produce a lot of batch operations and you cannot afford a failure in the middle of the batch.

The dual seal is the most logical of the back up choices. If the first seal fails the second seal takes over.


  • The API (American Petroleum Institute) gland, shown below, is another choice.
  • The disaster bushing (DB) will prevent leakage from spraying directly to the atmosphere.
  • Although not a positive seal, the leakage will be directed down the drain pipe (Q) where it can be collected.
  • Oil refineries often connect “Q” to a flare where volatile gases can be burned off.

  • In some designs the disaster bushing (DB) is replaced with several rings of packing.
  • Another function of the non-sparking disaster bushing is to help stabilize the shaft in the event of a bearing failure.