Question

d) The following figure is a diagram of a domestic hot water system. The gas valve is operated by the controller, which in turn, is operated by the temperature measuring and comparing device. The gas valve operates the main burner in full-on/full-off modes. The check valve in the water inlet prevents reverse flow due to overpressure in the hot-water system, and the relief valve opens when system pressure exceeds 100 psi. Control of the temperature is achieved by the controller opening and closing the main gas valve when the water temperature goes outside the preset limits (140°-180°F). The pilot light always stays on. i) Formulate a list of undesired (or initiating) events ii) Do a failure modes and effects analysis of the system. iii) Do a qualitative criticality ranking. Hot Water Faucet (normally closed) Flue Cold Water Check Valve Reliel Valve Temperature Measuring Comparing Controller Stop Valve Gas Figure P3.8. Schematic of domestic hot water system.

Answer 1

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