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Experience Reports and Frequently Asked Questions (FAQ) For Specialized Companies

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Trouble shooting overpressure and vacuum type leak detector systems

The following documents will help you trouble shoot problems with our leak detector systems:

ASF pdfTrouble shooting overpressure leak detectors D9 and D29

ASF pdfTrouble shooting overpressure leak detectors D25 and D26

ASF pdfTrouble shooting vacuum type leak detectors


What types of leak detection systems exist and what are the differences?

The DIN EN 13 160 describes 5 classes of leak detection systems:

Class I describes the leak detection systems based on the over- or under-pressure principle. The main advantage of this method is that a leak in the double-walled interstitial space, above and below the liquid level, is detected and reported, before fluid leaks into the environment. Because of the functional design over- and under-pressure systems prevent the spillage of liquid after an alarm output for a certain period of time up to an immediate fix of the problem.

All other classes have the disadvantage that prior to a leak detection liquid may have escaped already in the environment.

Class II describes monitoring systems, which are filled with a special leak detection fluid. These systems are permitted in Germany for new buildings only in above ground plants, - also components of the monitoring fluid are also classified as hazardous to water. When refilling the monitoring fluid it must be checked if the miscibility with the previous monitoring fluid is attested. Failure to comply can lead to fungal growth within the monitoring system and thus cause a functional impairment of the leak monitoring device.

Class III systems are based on liquid- and/or gas sensors, which detect leaked liquid or gas.

Class IV systems show with a certain probability a given value of the change of the tank content.

Class V systems can show a loss of liquid in tanks or pipelines below the liquid level (e.g. by incorporation of liquid sensors in the ground near the tank / pipe).


How works an over- or under-pressure leak detector?

ASF pdfClass I leak detection, how it works

FAQ 3-1Overpressure leak detector:

If a leak occurs a positive pressure in the interstitial space itself provides that air (or inert gas) from the interstitial space flows into the container or escapes from damage to the outer wall to the outside.

The pressure is designed that even when reaching the alarm set point the pressure in the interstitial space is at least 30 mbar above the max. hydrostatic generated pressure inside the tank. At pipelines min. 1 bar above the max. operating pressure of the inner tube.


Overpressure leak detector alarm:

During a leakage the leak monitoring fluid flows from the interstitial space in the tank interior or exterior.

The pressure in the interstitial space is reduced.

The internal pump compensates for small leaks and the pressure is built up again.

If the leakage is too large, the pump can not compensate for this and the pressure continues to drop until the alarm value.

Note: Positive pressure systems indicate an alarm by pressure reduction.

Video presentation:France SMLEngland SMLGermany SML


FAQ 3-2Vacuum leak detector:

When a leak occurs a negative pressure in the interstitial space provides that fluid from the inner container (or outer wall) is sucked into the interstitial space. The vacuum is designed in a way that even when reaching the alarm set point value the negative pressure in the interstitial space is at least 30 mbar above the max. hydrostatic generated pressure inside the tank. There are two types of vacuum systems:

High Pressure System - Typically, the connections for leak detectors are mounted above the tank (e.g. double-walled steel tanks).

Low pressure system - The suction line of the leak detector must be conducted to the low point of the interstitial space (e.g. in single-walled tanks with flexible leak protection lining).


Vacuum leak detector alarm:

Leakage above fluid level (air leakage):

Leakage air is sucked through the vacuum in the interstitial space.

The vacuum in the interstitial space is reduced (pressure increases).

The internal pump compensates for small leaks and rebuilds the required negative pressure again.

If the leakage is too large, the pump can not compensate for this and the pressure continues to rise up to the alarm set point.


FAQ 3-3Leakage below liquid level (liquid leak):

Liquid is sucked through the vacuum in the interstitial space.

Due to the volume reduction the negative pressure is reduced in the interstitial space (pressure increases).

The pump rebuilds the vaccum, more fluid is aspirated.

Once the liquid level reaches the opening of the suction line, liquid is sucked into the suction line, thus interrupting the pneumatic connection of the suction line to the interstitial space and the measuring line.

The pump sucks up more liquid, the liquid barrier is filled until the float valve closes.

The pump is still operating, the vacuum created holds the liquid column at the float valve closed.

In the measuring line continues to be a negative pressure, fluid is sucked further into the measuring line until the vacuum in the measuring line is broken up by the volume change up to the alarm set point.

Video presentation:France SMLEngland SMLGermany SML


What can be the cause for an alarm on leak detector?

This question can not be answered generally. The causes that lead to an alarm condition at the leak detection system can be very complex. Causes may be for example a leak in a tank wall or the leak detector itself, in the connecting pipes or fittings connected. Do not perform any repair work on the leak detection system by yourself, because further damage, not visible from outside, can occur. Hire a qualified contractor.


How often should a functional test be performed on the leak detector?

Trade associations, professional firms and manufacturers of leak detectors recommend an annual functional test of the leak detector system by an expert.

Most specialized companies offer this service by maintenance contracts.

Remember - a regularly checked leakage protection device offers maximum reliability. After the functional test, insist on receiving a test report that certifies the functionality of your system.


Where can I get replacement parts for a leak detector (e.g. green power light)?

Please see the note in the menu item "Spare parts" in the "Service" menu.


How often do the dry beads need to be exchanged in the air dryer at a pressure leak detector (type D9 or D29)?

FAQ 10-1For leak detection systems according to the principle of positive pressure the interstitial space may be filled with a maximum of 10% rel. humidity to prevent condensation and thus corrosion in the interstitial space. To achieve this, either a dry inert gas (e.g. nitrogen) or, in leak detectors with an integrated pump, a built-in air dryer in the suction line is used.

The size of the air dryer will depend on the above-ground or under-ground installation of the tank / pipe and the volume of the interstitial space. For details please see the documentation for the respective leak detector. The life time of the dry beads to saturation is around 12 - 15 months, but may also differ depending on the environmental conditions. Saturated dry beads may be identified by a color change. Saturated dry beads must be replaced.


How often, how long runs the pump/compressor of a leak detector?

The on / off frequency and the duty cycle of the integrated pump to compensate for minimal leakages, depends on the volume of the interstitial space and tightness conditions of the whole system. The pump has the task to compensate for minimal leakage in the system. The on and off of the pump at timed intervals without alarm output is normal and does not require any special measures.

Basically, the smaller the tank, the more often the pump runs, but in each case for a shorter period. For large tanks the pump runs less often, but then works longer to shutdown.

In vacuum leak detectors for the high pressure system (higher switching values), the pump basically runs longer per power cycle than in low pressure systems (lower switching values), with the switch-in return is lower than for low pressure systems.

Is the starting frequency of the pump increasing more and more, this points to an increasing leakage. If the pump runs until shutdown are getting longer or even constant, this may also indicate a large leakage, or the pump itself no longer reaches the required cut-off point.

In both cases, you should inform the specialist as a precaution, because otherwise an alarm condition can occur in the foreseeable future.


How much are the annual operating cost of a leak detector?

Similar to the terms of the pump of a leak detector, the operating costs depend on the state of your system and the type of the leak monitoring system used (low-pressure or high pressure system).

Basically, however, the operating costs in normal conditions of the installed system are relatively low. This amounts at a low pressure system to only 2-3 € / year, with a high pressure system according to the tightness 2-5 €. For comparison: A 42 "LCD TV (140 watts) produces at an average operating time of 3.5 hours / day around 35 euros in electricity costs / year.