An underpressure is created and maintained by the leak detector in the interstitial space.
In case of a gas leak, air or vapour are sucked into the interstitial space causing a underpressure decrease in the system.

Small leaks or untightnesses are compensated by the pressure pump. Relevant leaks can not by compensated due to the limited  pump volume flow. The underpressure continues to decrease. When the alarm pressure is reached, the optical and acoustical alarm is triggered.

In case of a liquid leak, stored product or groundwater is sucked into the interstitial space. The underpressure decreases and the pump is switched on to reestablish the operational underpressure.

Within some time the stored product or the groundwater is sucked into the suction line of the leak detector and into the liquid stop valve. The liquid stop valve closes and disconnects the pump from the interstitial space. The pump is not any more able to produce underpressure in the interstitial space.

The underpressure still existing in the interstitial space and in the measuring line will decrease by more liquid sucked in.

When the alarm pressure is reached the optical and acoustical is triggered.
In case of the alarm, the underpressure in the interstice is still high enough, that no stored product can enter the environment. 

Calculation of the alarm pressure

The alarm pressure shall be minimum 30 mbar higher, than the pressure resulting out of the geodetic height between the T-joint (suction-/measuring-line) and the deepest point of the double walled pipe.  


Aspects to keep in mind:

With vacuum leak detection systems in case of a leak, stored product or vapors of the stored product will enter the interstitial space, the connection linings and the leak detector.

All the equipment must be sufficient chemical resistant to the product and to the vapors.

In case of possible hazardous atmospheres, the equipment shall be explosion proof.

3-D Animations

Monitoring of a pipe with vacuum
Monitoring of several pipes with vacuum