The PSV in cooling water line at the outlet of a heat exchanger is actually a thermal safety valve and is used to relieve overpressure due to thermal expansion of water.

Comparison of PD meter, turbine meter & Coriolis meter in Custody transfer applications..(Accuracy wise)

A PD meter, a turbine meter or a coriolis meter may all be used in custody transfer. A PD meter or a turbine meter typically deliver accuracy around 0.5% and contain moving parts and require more maintenance and indicate volumetric flow. A good coriolis meter involves almost no wear and tear, needs less maintenance effort, delivers accuracy close to 0.1% and directly indicates mass flow. For custody transfer of gas service ultrasonic multi-path flow meters are also used with accuracy up to 0.35%. They are maintenance free and having very good diagnostic features.