The level indicators work with easily flowing bulk materials with big enough pour angle. Only such bulk materials generate an appropriate activation pressure on the membrane. The level indicators are usually installed at or in the silo wall. The necessary activation pressure depends on the design of the installed compression spring. The standard spring (20p) requires an operating pressure of approx. 20p to 50p. If stronger return springs are installed, the necessary activation pressure is accordingly higher. Two stronger return springs / exchange springs (60p; 250p) will be delivered free of charge with the level indicator.