DIN ISO 21360-1:2025-04

In this part of ISO 21360 three methods for measuring the volume flow rate and one method each for measuring the base pressure, the compression ratio, and the critical backing pressure of a vacuum pump are specified. The first method for measuring the volume flow rate (the throughput method) is the basic concept, in which a steady gas flow is injected into the pump while the inlet pressure is measured. In practice, the measurement of gas throughput may be complicated or inexact. For this reason, two other methods are specified which avoid the direct measurement of throughput. The second method for measuring the volume flow rate (the orifice method) is used when there is very small throughput at very small inlet pressures (under a high or ultra-high vacuum). It is based on measuring the ratio of pressures in a two-chamber test dome in which the two chambers are separated by a wall with a circular orifice. The third method for measuring the volume flow rate (the pump-down method) is well suited for automated measurement. It is based on the evacuation of a large vessel. The volume flow rate is calculated from two pressures, before and after a pumping interval, and from the volume of the test dome. Different effects, such as leak and desorption rates, gas cooling by nearly isentropic expansion during the pumping interval, and increasing flow resistance in the connection line between test dome and pump caused by molecular flow at low pressures, influence the results of the pressure measurement and the resulting volume flow rate. The choice of the required measurement methods depends on the properties of the specific kinds of vacuum pump, for example the measurement of the critical backing pressure is only necessary for vacuum pumps which need a backing pump. All data that are measured on a vacuum pump, but not specified in this part of ISO 21360 (such as measurement of power consumption), are defined in the specific pump standard. This second edition of DIN ISO 21360-1 replaces DIN ISO 21360-1:2016 and includes the following changes: a) Note in 3.3 has been deleted or amended; b) K_O in 3.7 has been corrected; c) 3.9 the definition of the volume has been changed to "is the volume of transported gas"; d) Figure 1 has been corrected; e) Figure 2 has been corrected; f) 5.2.7: change to "for at least 60 s" instead of "for the following minute". This document has been prepared by Working Committee NA 060-07-01 AA "Vakuumpumpen" ("Vacuum pumps") of Technical Section "Vacuum technology" at DIN Standards Committee Mechanical Engineering (NAM). It is the German translation of the International Standard ISO 21360-1:2020. ISO 21360-1 has been prepared by Technical Committee ISO/TC 112 "Vacuum technology".