ANSI vs API Pumps: What’s the Difference

ANSI and API are two process pump styles that are sometimes confused. This uncertainty can lead to users choosing a less expensive ANSI pump when the application demands API (or at the very least, an API pump could do the job more efficiently at a lower operating cost). Less often, a user may choose the more expensive API pump when an ANSI pump could effectively handle the job.

So, what’s the difference between ANSI and API process pumps?

First, what’s an ANSI pump?

ANSI process pumps are horizontal, end suction, single stage centrifugal pumps with an overhung impeller and back pull out. Their defining feature, however, is their interchangeability across manufacturers and brands. They must meet dimensional standards set by the American National Standards Institute (ANSI), making them identical in interface and envelope dimensions regardless of who makes them.

ANSI B73.1 standards set key dimensions for each of 27 centrifugal pump sizes, giving end users a range of options. ANSI pumps are also available in a wide range of specifications:

  • Flow rates from 10 to 5,000 GPM
  • Total head pressure from 50 to 750 feet (22 to 325 psi),
  • Horsepower from 1.0 to 250

Applications and Uses for ANSI Pumps

ANSI pumps are most often used to transfer thin fluids such as water, alcohols, and other less aggressive fluids. They can move fluids with or without solids depending on the impeller type. They can also be made with high hardness materials and alloys for use in more demanding and corrosive environments.

ANSI pumps have been a staple in the chemical industry for decades. They’re also commonly used in food processing, pulp & paper, textiles, general manufacturing, and other typical process plants.

In recent years there has been much discussion on adapting ANSI pumps for expanded use in the oil and gas industry—the domain of the API pump. To meet the environmental demands of the field, the pumps must meet additional standards such as reliability in extreme conditions.

Benefits and Drawbacks of ANSI Pumps


  • Dimensional interchangeability across manufacturers and brands gives the end user more options
  • Users can switch pumps without having to reconfigure the motor, coupling, impeller, bedplate, volute or piping location
  • ANSI pumps and parts are readily available
  • Less expensive than API pumps
  • High tolerance for solids with the right impeller type

Drawbacks: ANSI pumps typically don’t work well for moving thicker and/or viscous fluids. They typically don’t work as a replacement for other centrifugal pump types.

Now, what is an API pump?

API pumps meet Standard 610 for General Refinery Service as set by the American Petroleum Institute (API). This U.S. trade association for the oil and natural gas industries develops standards for petroleum and petrochemical equipment.

Unlike the ANSI standards, which are dimensional, API Standard 610 centers around the pump’s construction and design, particularly as they pertain to the pump’s ability to handle high temperatures, pressures and emissions.

Applications and Uses for API Pumps

API pumps are the choice for more aggressive applications in the oil refinery industry. Their casings, bearing houses, mounting feet and back cover arrangement are all designed for maximum efficiency and reliability in oil refinery applications, as well as controlling emissions and safely handling fluids that can cause environmental damage.

For example, look at the difference in casing design ratings between ANSI and API pumps:

ANSI Pump Rating: 300 psig at 300℉

API Pump Rating: 750 psig at 500℉

Benefits and Drawbacks of API Pumps


  • Built to withstand much higher temperatures and pressures
  • More capable of handling fluids that cause environmental damage
  • Designed to control emissions as required by the EPA

Drawbacks: API pumps are more expensive. They’re not as flexible or readily available as ANSI pumps.

Choosing a Pump: ANSI or API?

In general, ANSI pumps provide reliable service across a range of applications and are the pump of choice for chemical processing. They offer tremendous flexibility and ease of operation. API pumps are heavier duty and should be considered for higher pressure and temperature applications. They are the pump of choice for aggressive oil refinery processes.

There is more to pump choice than reliability, effectiveness and cost. Whether you’re pumping chemicals, wastewater or oils, safety is paramount. Any decision must take into account the specific operating conditions and the properties of the fluid being transferred.

For assistance choosing an ANSI or API pump, the experts at C&B are here to help. Let us help you find the best fit for your application. Contact us today.

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