Description of BS ISO 21360-1:2020 2020
This document specifies 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.
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, e.g. 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 document (e.g.
measurement of power consumption), are defined in the specific pump
standard.
About BSI
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