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Leak Detector Self-Test Option

Many blow molders have a policy of regular, manual verification of correct leak detector operation. This usually consists of running test bottles, with known size holes, through the leak detector. Typically, this may be done hourly.

Disadvantages of Manual “Test Bottle” Verification:

Labor intensive
Test holes in bottles can easily close up or become contaminated.
Bottle can be damaged by repeated testing, so that it is no longer representative. It may, for example, have a damaged neck that leaks air in addition to the test hole.
Test bottles are cold, producing a pressure decay that is greater than a warm bottle would, leading to false confidence in the leak tester.
Difficulty of creating small sized, accurate holes in plastic.
Test bottles must be clearly marked and stored so that they are not accidentally packed.
On some bottle handling systems, it can be difficult to retrieve a test bottle that has been incorrectly accepted.

The Alternative

An alternative is to fit automatic self test to the leak detector.

This automatically checks the correct operation of the leak detector by periodically introducing a known leakage into each test channel, and checking that the bottle is rejected. This can be either done under program control after a set number of cycles, or upon operator request, or both.

This is intended to reduce or eliminate the requirement for Quality Control staff to periodically run sample bottles through the system.

The system works by using a valve to connect an orifice (to atmosphere) into the pneumatic circuit that includes the bottle. This arrangement is duplicated for each channel in the case of multi-head leak testers. During the test cycle, this valve is switched on allowing some of the air in the bottle to leak back through the orifice, to atmosphere. It is as if the orifice is a hole in the bottle. Because the test is done on the bottles as they are being produced, the test is truly representative and all of the disadvantages above are eliminated.

Advantages of Automatic Self Test Option

Can be made fully automatic, saving labor.
The orifice is manufactured out of Stainless Steel  so it is accurate and dimensionally stable.
“Fresh” bottles are used for every test.
Test bottles are at a representative temperature.
Because it is inside the leak tester, operating from dry clean air, it is not susceptible to contamination.
The orifice can easily be changed where required, for a different orifice size.
No possibility of packing test bottles.
Can be practically done more often than a manual system.

If the leak tester fails the self-test, then a “SELF TEST FAILED” message appears on the display and an alarm can optionally be brought on. (If an operator normally initiates the testing, then an alarm is not really required).

The self-test option can be retrofitted to existing installations where required. It is available across our range of leak detectors.

 

 

© Plastech Control Systems. Page updated 10 December 2002