If the leak detector VLR.. is used in conjunction with an installation kit (junction between suction and measuring line) the pneumatic connections of the leak detector have to be flared unions (FU).
The connection typ versus the interstitial space is defined by the installation kit, e.g. QU8/6
For installation kits for the connection to the double walled pipe go to: Inst.kit pipe connection
For the monitoring of "Sensor(Float Switch) with Housing, with tilt-function" the use of leak indication unit LAE is recommended.