The Industry-Standard Specification for Horizontal Process Pumps
The Hydraulic Institute’s specification for general purpose overhung rotodynamic pumps provides a standardized framework for specifying, purchasing, and verifying single-stage, overhung-impeller centrifugal pumps—the category that includes all ANSI B73.1 process pumps. If you write pump specifications or evaluate supplier quotations, this specification is your reference document for ensuring that the pump you order meets recognized industry standards for design, materials, testing, and documentation.
What the Specification Covers
The specification addresses the complete pump package, not just the hydraulic end:
Design Requirements
- Impeller: Fully enclosed or semi-open design, keyed to the shaft, with front and (optionally) back wear rings. The impeller must be dynamically balanced to ISO 1940 G6.3 or better.
- Casing: Centerline discharge for horizontal pumps; foot-mounted. Designed for the maximum allowable working pressure (MAWP) at the maximum operating temperature. The casing must include a renewable wear ring opposite the impeller front ring.
- Shaft: Sized to transmit the maximum power across the full operating range without the shaft critical speed falling within the operating speed range (typically 20% above maximum operating speed minimum).
- Bearing housing: Designed for oil bath, oil ring, or grease lubrication. The L10 bearing life must be a minimum of 17,500 hours at maximum continuous operating conditions (ANSI B73.1 requirement) and preferably 25,000+ hours at rated conditions.
- Seal chamber: Dimensions per ANSI/ASME B73.1, accommodating standard mechanical seals (single cartridge, dual cartridge, or component). The seal chamber must provide adequate flush flow and heat removal for the specified seal type.
Material Requirements
The specification references standard material classes. For ANSI B73.1 pumps, the most common specification is the ASME B73.1 material class table, which defines casing, impeller, shaft, and wear ring materials for different service conditions—from Class 1 (all iron, for general water service) to Class 5 (high-alloy for corrosive chemical service).
Testing and Inspection
Per the HI specification, every pump must receive a hydrostatic test of the casing at 1.5× MAWP (minimum), an impeller balance check, and a performance test per HI 14.6. Optional tests include: witnessed performance test, NPSHr test, vibration test per HI 9.6.4, sound level test, and a complete dimensional inspection against the certified outline drawing.
Documentation Requirements
The specification defines the minimum documentation package: certified outline drawing, cross-section drawing, performance curve, NPSHr curve, material certificates, hydrostatic test report, and installation/operation/maintenance manual. For critical-service pumps, additional documentation (rotor dynamic analysis, bearing life calculation, seal environment report) should be specified in the purchase order.
Writing a Pump Specification for Your Next Purchase?
Our team can help you develop a specification that references the appropriate HI standards and ensures competitive bids are technically comparable—eliminating the common problem of comparing pumps tested to different standards.
Key Takeaways
- The HI specification provides a standardized framework for specifying overhung rotodynamic pumps, ensuring all suppliers bid to the same technical requirements.
- Require a minimum L10 bearing life of 25,000 hours at rated conditions in your specification—the ANSI minimum of 17,500 hours is a floor, not a target.
- Specify the performance test grade (HI 14.6 Grade 1E minimum for process pumps; Grade 1U for critical service) in your purchase order.
- Documentation requirements should match pump criticality: basic packages for utility pumps; comprehensive packages including rotor dynamics and bearing life analysis for unspared critical-service pumps.