By Ken Kugler, Executive Officer – Standards, Pump Industry Australia Inc.
*This is a second discussion on pump test acceptance grades based on the Hydraulics Institute white paper for Understanding the Effects of Selecting a Pump Performance Test Acceptance Grade.
The introduction of AS ISO9906: 2018 has opened the Australian pump industry to a wider range of pump test acceptance tolerances that may be requested by a purchaser. This article continues on from the discussion in part one, and will look briefly at the relation between the various acceptance tolerances, pump system application, pump delivery lead times and energy consumption.
Table 1, extracted from ANSI/HI14.6 (similar to ISO9906), provides the acceptance grades with their particular tolerances, but how is the best way a specifier can nominate a particular acceptance grade? The selection of an acceptance grade determines the performance tolerance of a pump test agreed upon by the user and the manufacturer.
While these tolerance bands include the accuracy of the measuring equipment, it is only a very small portion of the total allowable tolerance. The majority of any variations in performance may be due to a number of issues related solely to the pump, and perhaps the pump driver.
As a guide to the purchaser, AS ISO9906 and HI ANSI14.6 both include a table of ‘Default test acceptance grades’ for a factory test where a guarantee point has been given but no acceptance grade is specified. The table is based on the selection of eleven industry applications, where applications are nominated simply as ‘Electric power industry’ or ‘General industry’ or similar.
Should a purchaser not specify an acceptance grade and the ‘Default test acceptance grade’ table is utilised, the standard only requires the head and flow to be guaranteed. There is no requirement for the manufacturer to provide a guaranteed power and/or efficiency. A purchaser needs to provide a clear and acceptable specification for a factory pump test to achieve a satisfactory outcome for both parties.
Diagram 1 illustrates in a general form some typical applications and how an acceptance grade may be decided upon and selected.
Today, with a worldwide focus on energy consumption, it is presumed power and efficiency will always be a consideration in the decision to nominate an acceptance grade. But higher degrees of accuracy in testing and performance may come with an impact on cost and delivery.
Depending on the pump size, design and the manufacturing operations, an increase in performance will come with varying cost implications.
Simply, the higher the precision used in manufacturing and testing, the smaller the expected variations in test results. Perhaps with a smaller pump, the variation in cost by the manufacturer to guarantee a better efficiency may outstrip the cost of the additional power necessary over a given period.
The Hydraulics Institute white paper provides in Table 2 an illustration of possible impacts on costs and delivery on tighter acceptance grades. This is very general, pump manufacturers will all differ in their approach and outcome on testing costs and delivery.
Previously, we noted that one of the most important reasons to have a manufacturer test a pump is to have baseline data for diagnostic purposes in the future and that almost any acceptance grade might suffice. All pumps are installed into a system of some description, and the system resistance curve (flow against head) of the piping system is predominantly a calculated curve or value.
It is only via the installation of a factory-tested pump into the system that enables system resistance to be verified at commissioning.
However, it is rare to look upon the pump and system in this way. Typically, an initial pumping/piping system problem is often diagnosed as a pump underperforming; perhaps it has a lower than expected head and is using more power, or generating too much head as the case may be.
It is a factory-tested pump with its guaranteed performance curve that will potentially rule out a genuine pump underperformance on site. Any future degradation in either pump or the piping system will more easily be identified over the operating lifetime.
The Hydraulics Institute white paper for Understanding the Effects of Selecting a Pump Performance Test Acceptance Grade and a webinar are available online at no cost. Its 17 pages are much more explanatory on many other issues, including crossing steep or shallow system curves, the interactions or trade-offs between each acceptance grade, the intended operating system, possible cost and delivery implications.
It is recommended that engineers specifying and requiring manufacturer tested pumps take the time to read and understand the benefits and possible implications of nominating a particular acceptance grade. The white paper can be found on the Pump Industry Australia website https://pumps.org.au/product-category/publications/.