5.5 Contractual testing5.5.1 Tolera

5.5 Contractual testing5.5.1 Tolerance magnitude near optimum efficiencyFour tolerance grades are given in Table 2 for the fan volume flow, pressure, shaft power and sound power level (see also Figure 1). In the normal case these grades are applicable to all contractual agreements between the purchaser and his supplier, and if not, a separate agreement should be obtained. The operating point is assumed to lie where the efficiency, as stated by the supplier, is at least 0,9 times the stated best efficiency ηopt. Outside this range, tolerances are applied as detailed in clause 5.5.2