A light metal case supports the membrane. The membrane is held by a ring of non-corroding material screwed onto the case. The membrane is pre-stressed by a spiral spring.
The pre-stressing of the membrane can be increased if you exchange the spiral spring inserted with one of the stronger spiral springs.
This is important for:

• Bulk materials with particularly high specific weight,
• Bulk materials with a certain aggressiveness,
• Conveyence with low positive pressure.

If you convey with higher pressure within the silo, a simple pipe can adjust the lower air pressure which prevails behind the membrane in the level indicator.
The operating point of the micro switch can be changed as the micro switch is movable.
Advantage: The sensitivity of the level indicator can be adjusted to the:

• character of the bulk material,
• installation conditions.

Level indicator FMN 113 can also be used with wet bulk materials.