The protection of any vessel (filter, silo, mill, bin, etc.) is achieved through the installation of one or two dynamic pressure sensors and one or more HRD suppressors.
The suppression bottle is activated through a gas generation system (a gas generator similar to the ones used for car air bags), which replaces the old pyrotechnic actuators. Whenever an explosion is detected the gas generator activates and generates pressure inside the valve’s head so that a mechanical pin releases opening the valve’s flap and spreading the extinguishing powder inside the vessel (the system exploits the pushing strength of nitrogen stored at 60 bar).
In order to grant the reliability of the activating system the gas generator is redundant (that is there are two gas generators in parallel on the head of each suppression bottle).
The third generation PXD multisensor for explosion protection detects pressure in a dynamic way and replaces the old static membrane sensors.
This sensor checks continuously the pressure values inside the volume to be protected: when pressure increase dp within a precise time interval dt becomes higher than the programmed value, the sensor sends immediately an alarm signal to the control unit.
The sensor has an internal memory where, by a PC, the values dp, dt and Pmax are recorded; The setting of those values depends on many factors such as the volume to be protected, the characteristics of processed dusts, the operating temperatures, etc: the choice of reference values is different and specific for any installation. In the sensor memory are also recorded the pressure values measured during any alarm in order to make it possible to retrace the history of any event.
The PXD sensor is made up of a piezoceramic cell which detects pressure level and converts the pressure value detected into an electrical signal which is continuously processed by the control unit. Usually two PXD sensors are installed on the vessel, which work independently one from the other. In order to reduce the risk of false activations the sensors work according to “AND” logic (they both must send the alarm signal in order to activate suppression). In case one of the two sensors gets faulty the system automatically skips to “OR” logic, in order to grant the functioning continuity of the suppression system.