Glossary B

Back plate

  • Used in some centrifugal pumps to position the stuffing box and provide an impeller wear surface.

Back pull out pump

  • A design that allows the wet end of the pump to be left on the piping when the power end and adapter are removed. A.N.S.I. pumps are designed this way.

Back to back double seal

  • The rotating seal faces are facing in opposite directions. The worst possible configuration. In the past this term was used to describe a higher barrier fluid pressure between dual mechanical seals.

Balanced seal

  • A design in which the seal face closing area is reduced to lower the closing force, and reduce the heat generation between the faces.

Balance Ratio

  • A 70/30 balance ratio means that 70% of the seal face closing area is seeing the stuffing box pressure and 30% is not seeing the pressure.

Ball bearing

  • Consists of an inner race, an outer race, and a series of balls between them. Often called a precision or anti friction bearing.


  • Metric term for one atmosphere of pressure.

Barrier fluid

  • The high pressure fluid that is circulated between two mechanical seals. The fluid should enter the bottom and leave the top to prevent air pockets.

Base plate

  • The pump and motor mount on this unit. The pump and motor feet closest to the coupling should be doweled to the base plate.


  • The mechanical seal drive lugs wear into the drive slots and prevent the seal faces from moving forward to compensate for wear.


  • Supports the rotating shaft and allows it to turn with a minimum amount of friction. Could be either sleeve or anti-friction type


  • Can be manufactured from metal or non metallic materials to eliminate flexing, rolling or sliding elastomers in mechanical seal designs.

Bellows plate

  • A thin, stamped disc. Two are welded together to form a convolution.

Bernoulli’s law

  • A moving stream of liquid or gas exerts less sideways pressure than if it were at rest. The result is that things seem to be drawn into the stream, but they are really being pushed in by the higher pressure from outside.


  • The best efficiency point. It is the point where the power coming out of the pump (water horse power) is the closest to the power coming into the pump (brake horse power) from the driver. This is also the point where there is no radial deflection of the shaft cause by unequal hydraulic forces acting on the impeller.


  • Brake horse power. The actual amount of horsepower being consumed by the pump as measured on a pony brake or dynamometer.

Body bound bolts

  • The bolt has an interference fit with the bolt hole.

Brinnell hardness

  • A method of measuring the hardness of metal parts and hard seal faces. Above 350 the standard machining operations of turning, boring, drilling, and tapping become uneconomical.

Buffer fluid

  • The low pressure fluid that is circulated between dual mechanical seals.

Buna N

  • Some times called Nitrile. A common elastomer used in the sealing of oil or water. Sensitive to Ozone attack and therefore has a short shelf life.


  • A close fitting support device used to restrict flow between two liquids, thermally isolate a hot liquid, support the rotating shaft, break down pressure etc. Commonly made of carbon or Teflon.

Bypass line

  • Used to either re-circulate fluid from the pump discharge to the stuffing box, the stuffing box to the pump suction, or the pump discharge to a lower pressure point in the system.


  • On February 09, 2018