
When deciding between two process pump styles, how do you choose the right one for your application? Numerous factors come into play, but the first step is distinguishing between ANSI and API pumps. While ANSI pumps adhere to standards set by the American National Standards Institute, API pumps follow the American Petroleum Institute’s more rigorous guidelines. Understanding their design intents, performance capabilities, and typical use cases is crucial to making an informed choice.
An Overview of API vs. ANSI Pumps
API and ANSI pumps reflect different engineering use cases. API pumps are manufactured to API Standard 610, driven primarily by oil, gas, and petrochemical industry demands. By contrast, ANSI pumps conform to ANSI/ASME B73.1 (or B73.2/3) and are favoured for a broader range of applications. ANSI pumps are especially versatile—offering dimensional interchangeability across 27 centrifugal pump sizes—making them suitable for sectors such as food processing, textiles, chemical synthesis, pulp & paper, and other industrial facilities.
API Pumps
API pumps, built to API 610, are explicitly tailored for high-stress environments typical in refineries and petrochemical plants. The standard covers more than 500 specifications—from casing and bearing design to emissions control and environmental safety.
Key characteristics of API pumps include:
- High temperature and pressure tolerance: Rated up to around 600 psig at 315°C, compared to ANSI’s 300 psig at 149°C.
- Robust casing and bearing housings: Heavy-duty steel, often with integrated cooling jackets.
- Closed impellers with wear rings: Enhances sealing, efficiency, and serviceability.
- Centerline mounting: Allows for thermal expansion with minimal stress on the casing.
- Compression-style back covers: Bolted directly to the casing for better sealing.
Advantages:
- Exceptional performance under extreme conditions.
- Built-in emission control and environmental compliance.
- Highly reliable in hazardous or high-pressure services.
Disadvantages:
- Higher acquisition and maintenance cost.
- Less flexible for general industrial use.
- Often involves longer lead times and specialised parts availability.
ANSI Pumps
ANSI pumps are designed to meet dimensional standards like ANSI/ASME B73.1. They are typically single-stage, horizontal centrifugal pumps with overhung impellers and back pull-out designs, benefiting from easy serviceability and part interchangeability.
Core attributes include:
- Modular design: With consistent interfaces across manufacturers, compatible in flow rates (10–5,000 GPM), pressures (up to 750 ft head), and horsepower (1–250 HP).
- Open or semi-open impellers without wear rings.
- Foot-mounted construction (usually), though centerline-mounted variants are occasionally available.
- Back cover held by bearing adaptor: Simplifies assembly, but may be less pressure-resistant.
Advantages:
- Lower initial and operating costs.
- Flexibility in configuration and adaptability across industries.
- High parts availability and ease of maintenance.
- Effective handling of solids with proper impeller selection.
Disadvantages:
- Not suited for highly viscous fluids or extreme pressure/temperature scenarios.
- Foot-mounting can lead to alignment issues with thermal expansion.
- Less durable in harsh conditions, due to thinner materials and simpler design.
Main Differences at a Glance
Feature | ANSI Pumps | API Pumps |
Standards | ANSI/ASME B73.x (dimensional) | API 610 (construction & safety) |
Pressure & Temp | ≈300 psi at ≈149°C | ≈600 psi at ≈315°C |
Impellers | Open/semi-open, no wear rings | Closed with replaceable wear rings |
Mounting | Foot-mount (some centerline) | Centerline-mount standard |
Bearing Housing | Lighter, simple | Heavy-duty, often jacketed |
Back Cover | Frame-adaptor gasket seal | Bolted compression gasket |
Fluid capability | Thin to moderate fluids | High-viscosity, aggressive fluids |
Which Pump Is Right for You?
Choosing between API and ANSI pumps depends on a thorough evaluation of your operating conditions, fluid characteristics, regulatory requirements, and operational goals.
1. Fluid type & operating conditions:
- Use API pumps for high-viscosity, corrosive, or toxic fluids—especially under elevated pressure or temperature.
- For standard industrial fluids (e.g., water, dilute chemicals), ANSI pumps are often sufficient and more economical.
2. Temperature & pressure profile:
- Exceeding ~150 °C or ~300 psig? Lean toward API.
- Within standard limits? ANSI remains a viable, cost-effective choice .
3. Safety and compliance:
- When handling flammable or regulated fluids, API’s rigorous design accommodates emission and containment regulations.
4. Maintenance & lifecycle cost:
- API pumps come with higher upfront costs, but their robustness often results in lower maintenance and longer lifespan for critical services.
- ANSI units offer higher flexibility and lower replacement part costs—with acceptable performance for general applications.
5. Operational environment:
- In processes subject to thermal cycling, API’s centerline mounting ensures better reliability. ANSI’s foot-mounted design may suffer from misalignment over time.
6. Budget and availability:
- If budget constraints or lead times matter more than extreme durability, ANSI’s lower cost and wide availability make it appealing.
7. Additional considerations:
- Pumps for swimming pools or similar light-duty uses clearly favour ANSI due to their design flexibility and affordability.
- Consider conducting an energy audit if energy efficiency and lifecycle cost optimisation are priorities; it may reveal that an ANSI pump, run at its BEP (best efficiency point), outperforms a misapplied API pump over time.
Conclusion
Whether you choose API or ANSI pumps hinges on balancing technical requirements with economic and operational priorities. API pumps offer unparalleled resilience and safety in extreme or regulated applications, while ANSI pumps are pragmatic, cost-effective workhorses ideal for general industrial use. Ultimately, assessing fluid properties, operating conditions, regulatory needs, and lifecycle costs will guide you toward the right fit. Evaluating these elements—not just price—ensures your process is efficient, reliable, and safe.