Furness controls FCO770, Руководство пользователя, Страница: 14 / 101

Page 14 FCO770 Users Guide Issue 1
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The bell or collection chamber is used to enclose the test item or a particular part of it. The
test item is then continuously pressurised during the test cycle from a separate pressure
source.
The bell chamber is connected to the "Test -" port of a standard pressure drop leak detector.
If the test item leaks, the air will be captured within the bell and the pressure in it will
increase. The pressure increase will be shown on the display as a positive leak reading.
By applying a low pressure to the bell from the leak detector the integrity of the bell can be
checked. If a seal is damaged or missing the FCO770 it will show as a negative leak reading.
Since both positive and negative fail levels can be set on the FCO770, the system guarantees
that every test is valid.
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This test does not use the differential pressure sensor, but checks the actual pressure in the
test item. There are two options for the blockage test:
1) The test item is pressurised to the required level and then isolated from the source. During
the test, the pressure must fall below a pre-set level to indicate that the product is not blocked.
A second fail level may be used to check that the flow was not too great indicating a large
(gross) leak.
2) For some test items the pressure may be lost too quickly to be able to discriminate with
method 1. In this case we have an option to continue filling during the test stage so that a
back-pressure test is performed.
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This test does not use the differential pressure sensor, but checks the actual pressure in the
test item. The test item is pressurised to the required level and then isolated from the source.
Test pressure readings are shown relative to the starting pressure. A pressure drop is shown as
a positive leak. There are separate fail levels for positive and negative leaks.
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The auto prefill function is useful where the test item is slow to fill or has a restriction in the
fill path. It may also be used as a cost-effective way of testing at different pressures without
manual adjustment or an auto-regulator. Auto prefill may be used with differential pressure
leak tests, blockage tests and coarse leak tests.
The method is to apply a pressure that is larger than the required test pressure, normally via a
restriction. When the pressure reaches the set prefill pressure level, the pressure source is
disconnected. The fill stage allows any residual test line pressure to finish filling the test item;
this is important when the test item has a restricted fill path since the measured pressure
during the prefill stage may be quite different from the final test pressure.