In 2011, the Hydraulic Institute updated their testing standards for centrifugal pumps (ANSI/HI 14.6 – Rotodynamic Pumps for Hydraulic Performance Acceptance Tests) to harmonize with international standards (ISO 9906) for common practices worldwide. Since the new standard is a more significant change for North America manufacturers, implementation has been slower to adopt.
Previously, acceptance grades were level A or B with tolerance values based on specific flow and/or pressure ranges – regardless of industry or pump type. In short, Level A allowed for no negative tolerance whereas Level B generally allowed for a -3% deviation from the contract performance. All certified tests at Wilfley were carried out to the higher standard (Level A).
The new guidelines recognize that different pumps and/or industries have differing needs and established a multitude of default acceptance grades based on the application and rated power of the pump:
| Application | Rated shaft power of pump | ||
| >10 to 100 kW (13 to 134 hp) | >100 kW (134 hp) | ||
| Municipal water and wastewater | 2B | 1B | |
| Building trades and HVAC | 2B | 1B | |
| Electric power industry | 1B | 1B | |
| Oil and gas industry | API pumps | 1B | 1B |
| Pipeline | 1B | 1B | |
| Water injection | N/A | 1B | |
| Chemical Industry | 2B | 2B | |
| Cooling tower | 2B | 2B | |
| Pulp and paper | 2B | 2B | |
| Slurry | 3B | 3B | |
| General industry | 3B | 2B | |
| Dewatering, drainage and irrigation | 3B | 2B | |
| Pumps not listed above | 3B | 2B | |
Note: The tolerance classes are for rated shaft power above 10 kW (13hp). For lower power levels, the default acceptance criteria is ±10% on flow, ±8% on head and efficiency or power are controlled by a special formula. Contact your pump manufacturer for details.
In general, the level of acceptable tolerance value increases from Grade 1 to Grade 3 and can either be unilateral (one sided) or bilateral (two sided). True to our nature, Wilfley decided to implement the new testing procedures based on the highest grade accounted for (1U).
Pump Test Acceptance Grades and Corresponding Tolerance Band
| Test Parameter | Guarantee Requirement | Grade | Grade 1 | Grade 2 | Grade 3 | |||
| ∆tQ | 10% | 16% | 18% | |||||
| ∆tH | 6% | 10% | 14% | |||||
| Symbol | Acceptance Grade | |||||||
| 1B | 1E | 1U | 2B | 2U | 3B | |||
| Rate of Flow | Mandatory | tQ(%) | ±5% | ±5% | 0% to +10% | ±8% | 0% to +16% | ±9% |
| Total Head | Mandatory | tH(%) | ±3% | ±3% | 0% to +6% | ±5% | 0% to +10% | ±7% |
| Power | Optional (either/or) | tP(%) | +4% | +4% | +10% | +8% | +16% | +9% |
| Efficiency | t(%) | -3% | -0% | -0% | -5% | -5% | -7% | |
As noted above, the default classification for chemical process pumps (ASME B73.1 or ISO 2858 pumps) is Grade 2B. This allows a bilateral tolerance band of up to 8% on flow, 5% on head and either 8% overage on power or 5% deficiency on efficiency. By contrast, we follow Grade 1U which has a tighter tolerance band (unilateral 10% versus bilateral 8% = 16 points) and no negative tolerance on flow, head or effiency. Therefore, the customer will get what they pay for with Wilfley.
Bilateral vs. Unilateral Tolerance Bands
 | Bilateral Tolerance Band Curve 1 = Fail Curve 2 = Pass Curve 3 = Pass Curve 4 = Pass |
 | Unilateral Tolerance Band Curve 1 = Fail Curve 2 = Pass Curve 3 = Pass Curve 4 = Fail |
As you can see, Wilfley is constantly striving to add value for our customers in every aspect of the company. Contact your local Wilfley representative to learn more.
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