The scheme above present three pressure transmitters (PT) connected to a logic solver. The solver will decide based on 2-out-of-3 (2oo3) voting whether or not to activate the final element. The final elements consist here of two block valves that stop flow to the downstream facilities (right) to prevent them from exceeding a maximum pressure. The operator of the plant is warned through a pressure alarm (PA) that the HIPPS was activated. This system has a high degree of redundancy:
- failure of one of the three pressure transmitters will not compromise the HIPPS functionality, as two readings of high pressure are needed for activation.
- failure of one of the two block valves will not compromise the HIPPS functionality, as the other valve will close on activation of the HIPPS.
One must not confine self to the above design as the only means of materializing the HIPPS definition. One must always think of the HIPPS generically, as a means of isolating a source of a high pressure when down stream flow have been blocked, isolating the upstream equipment (source of the high pressure) in a highly reliable manner. Be this source of the high pressure a pump (in case of liquid) or a gas compressor (in case of gas), the aim of the HIPPS in these cases is to reliably shut down the pump or the gas compressor creating the high pressure condition in a reliable and safe manner.
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