ANSI Specifications


A set of specifications (envelope dimensions) for centrifugal pumps manufactured in the United States. The following charts describe both the inch and metric dimensions:

Among the standardized dimensions you will find:

  • The locations of the pump hold down bolts.
  • The distance between the suction and discharge nozzle centerlines.
  • The height of the pump coupling.
  • The length of the pump

There are currently three overall standard pump lengths:

  • 17.5 inches or 445 mm
  • 23.5 inches or 597 mm
  • 33.875 inches or 860 mm.

The European equivalent of this standard would be the I.S.O. (International Standards Organization) standard. The European community has not totally adopted the metric dimensions proposed in the ANSI (American National Standards Institute) standard.

The ANSI standard has gone through several revisions since it was originally adopted and there is lots of talk about combining it with the API (American Petroleum Institute) standard to create a single standard for centrifugal pumps in the United States.

The main problem with this and similar standards is that they were written for packed pumps and are only now changing to reflect the increasing usage of mechanical seals. The most obvious change has been the acceptance of oversize stuffing boxes, but these standards still have a very long way to go.

Ultimately the ANSI committee is going to have to accept the fact that shorter pumps with very low shaft L3/D4 numbers is the logical approach for centrifugal pump designs incorporating mechanical face seals.

Many of the pump manufacturers oppose any change to the basic ANSI specifications because of the need for re-tooling the castings used to manufacture the present pumps.

There is also a set of dimensions for a metric version of the pump. Please take a look at the following chart:


  • On February 14, 2018