International Organization for Standardization (ISO)
Status
Latest
ISO 21360:2007
Scope
This International Standard is a basic standard which defines three different 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.
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 described 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 occurring at very small inlet pressures (in the high and ultra-high vacuum). It is based on
measuring the ratio of pressures in a two-chamber test dome where 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, e.g. the measurement of the critical backing pressure is only necessary for vacuum pumps which need
a backing pump. All data that is measured on a vacuum pump but not described in this International Standard (e.g. measurement of power consumption) is defined in the specific pump standard.
ISO 21360:2007 history
2007ISO 21360:2007 Vacuum technology - Standard methods for measuring vacuum-pump performance - General description