Explain your choice of a pressure-to-open (normally closed) or pressure to- close (normally opened) valve in the following scenarios:

a) A valve on a cooling water line which is used to cool down a reactor hosting an exothermic reaction

b) A valve on a water line heading to a treatment plant before being released in a river

c) A valve on a gas stream (containing SO2) going to an absorption tower before being released to the atmosphere