The impact of ISO 9906 ’s grade factors on pump efficiency.

“Grade” factor in the ISO 9906

Pumps are often tested to demonstrate that they can deliver the performance requested by the customer. Customers want to gain insight, for example, into the energy costs over the pump’s lifespan. These tests are carried out according to a standard, such as the ISO 9906 standard. This standard covers various aspects of pumps. Customers who have less knowledge about pumps, as it is only a part of their process, may quickly get the impression that they can compare different quotes based on efficiency by simply referring to this standard in their specifications. However, this assumption is incorrect.

The ISO 9906 test has different grades that determine the allowed deviation from the measurement result. Some grades allow for the deviation to be both above and below the specified value, and this can be up to 7%.

Below you can see the table indicating the efficiency grades in the ISO9906.

The table, for example, shows grade 1B, which allows for a deviation of -3 percent. This means that the pump supplier may, for example, indicate an efficiency of 81% in his quote according to grade B1, while in reality it may only be 78%. With a stated efficiency of 81% according to grade 3B, the deviation can even be 7%, which means that 74% still meets the standard in practice.

A pump offer with the text “tested according to ISO 9906 with 81%” without mentioning the grade can therefore result in a pump with only 74% efficiency

Some pump manufacturers use this trick to improve their efficiency figures. For example, if the efficiency of their pump is 79%, they offer to work according to the 3B standard, where a deviation of 7% is allowed. They then add, for example, 6% of this deviation to their efficiency, resulting in a nice figure of 85%, but it is then according to the 3B standard, which will only result in this case in a lower efficiency in practice.

Rodelta always offers its efficiency for drinking water pumps according to the 1U standard, which means that the specified efficiencies need to be actually achieved. However, a deviation upwards is allowed. This means that this way of specifying efficiency is more likely to show a slightly lower efficiency, as a deviation of one per cent in production may be normal. But with a 1U declaration, this deviation is immediately visible in the efficiency number.

Why are there different grades? It has to do with production processes. In mass production, not every product is tested, so production costs are lower. The gradation is then chosen more broadly, so that any deviations due to, for example, wear of casting moulds and less accurate finishing of the pump parts do not immediately lead to rejection. These production processes do not offer the precise guidance needed to ensure that all pumps achieve the higher gradations. The higher grades are easier to achieve with pumps that are produced individually. However, this does result in higher production costs.

For pumps that are not in continuous operation, the gain in efficiency and energy savings may not be decisive in choosing a more expensive pump in a Total Cost of Ownership calculation. However, for pumps that run more hours, the deviation in efficiency compared to the more expensive pump can quickly be recovered through savings in energy costs.