Glossary L

L/ D4

  • A guide line for determining pump shaft stiffness where the length of the shaft is compared to its diameter. This number should be below 60 in imperial units and 2.0 in metric units.

Labyrinth seal

  • A non contacting seal utilizing a tortured path for the escape of the fluid. Utilizes a series of pressure drops to reduce the leakage.

Lantern Ring

  • A device used to supply lubricant to packing. Usually located in the middle of the packing ring set.

Linear pressure drop

  • A straight line pressure drop across the lapped seal faces. Seldom happens.

Line bearings

  • Position the rotor or shaft radially. Normally of the sleeve type.

Line bored

  • When the drilling or boring is done on a jig that insures every component is in a straight line.

Lip Seal

  • See grease seal.

Low flow

  • A condition that can cause excessive heat inside the pump volute. A temperature rise of 10°C (18°F) across the operating pump is considered excessive. Usually caused by throttling a pump discharge valve.


  • Any fluid that will maintain a film thickness of one micron or more at its operating temperature and load.


  • On February 09, 2018