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I believe that the FRA rule about the need for pressure relief valves needs changing. Rule 8.8 says,
A certified pressure relief device [PRD] must be installed in each part of the pneumatics system where a different operating pressure is used (operating pressures separated by a pressure regulating device).
This should be rewritten:-
A certified pressure relief device [PRD] must be installed in each part of a pneumatic system where the equipment pressure rating is less than the pressure upstream of the pressure regulating device. (This is to protect that equipment from overpressure in the event of pressure regulator failure.)
My last heavyweight robot had 4 operating pressures (Bottle pressure, 16barg for the ram power stroke, 4barg for the pilot supply to the 5/2 solenoid valve and 1.5barg for the ram return stroke). It had 3 pressure regulators and only 2 relief valves. The high pressure one was set at 68barg and the low pressure one was set at just over 16barg. These were adequate to protect all the downstream equipment.
A certified pressure relief device [PRD] must be installed in each part of the pneumatics system where a different operating pressure is used (operating pressures separated by a pressure regulating device).
This should be rewritten:-
A certified pressure relief device [PRD] must be installed in each part of a pneumatic system where the equipment pressure rating is less than the pressure upstream of the pressure regulating device. (This is to protect that equipment from overpressure in the event of pressure regulator failure.)
My last heavyweight robot had 4 operating pressures (Bottle pressure, 16barg for the ram power stroke, 4barg for the pilot supply to the 5/2 solenoid valve and 1.5barg for the ram return stroke). It had 3 pressure regulators and only 2 relief valves. The high pressure one was set at 68barg and the low pressure one was set at just over 16barg. These were adequate to protect all the downstream equipment.
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