Revisiting the three-break protection for control valves: Seeking the pneumatic circuit diagram for three-break protection

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The last edit to this post was made by 328104062 on 2015-10-7 at 06:41. As the title suggests: I am looking for circuit diagrams for the above three scenarios, or circuit diagrams for any two of these combinations. 1. Loss of air supply: When there is a fault in the air supply for the control system (no air available), the pneumatic holding valve closes automatically, locking the output signal pressure in the diaphragm chamber of the pneumatic control valve. The output signal pressure then balances out with the counterforce generated by the spring in the control valve, resulting in the valve remaining in its faulty position. This pressure holding valve should be set to activate at a value slightly below the minimum of the air supply. 2. Power shutdown: When there is a power failure in the control system, the power-loss signal comparator causes the output voltage of the single-electrovalve solenoid directional control valve to disappear. As a result, the solenoid directional control valve loses power; the spool inside it slides under the action of the return spring, causing the solenoid valve to change direction. This leads to the evacuation of pressure from the diaphragm chamber of the pneumatic holding valve, which then closes. The output signal pressure is thus locked within the diaphragm chamber of the pneumatic control valve, where it balances out the counterforce generated by the valve’s spring. As a consequence, the position of the pneumatic control valve remains at the fault position. 3. Signal cutoff: When there is a fault in the control system signal (loss of signal), the power-loss detector detects this and cuts off the voltage signal to the single-electrovalve solenoid directional control valve. As a result, the solenoid valve loses power; the spool inside it slides under the action of the return spring, causing the valve to change direction. This action empties the pressure in the diaphragm chamber of the pneumatic hold-down valve, which then closes. The output signal pressure is thus locked within the diaphragm chamber of the pneumatic control valve, where it balances out the counterforce generated by the valve’s spring. As a consequence, the position of the pneumatic control valve remains at the faulty position. The position feedback signal is provided by the valve position signal returner.