Essentially the manufacturer will try to limit the number of visits by a customer appointed inspector. This gets in the way of production. In the old days, the inspector would come in to witness hydrotest on the individual components and then arrange to return for testing of the assembled valve. This meant no main production until the hydro was witnessed and signed off. Still occurs dependant on the purchasers requirements.
To answer your question, these days most manufacturers will get ALL their body, bonnets and nozzles and caps (if cast) done up front individually and certified anyway (most times by an offshore producer that does the casting, machining and hydrotesting). This is what ISO-9001 maintained control allows them to do. Doing it this way allow multi use of all of these parts (ie., it covers most, if not all, offerings).
Typically in this day and age, final physical inspection will consist of;-
*Check of nameplate, casting heat nos., materia certification etc.
*Set pressure test
*Leakage test
*Bellows integrity test if applicable
*Hydro test (nozzle only on built valve using test gag adaptor - only if nozzle cast and not already done)
*Pneumatic shell test - already done by the manufacturer but may be wanted for inspectors that know about it (basically checking the seals of the valves between body/bonnet, cap. nozzle etc.)
Note: May vary between manufacturers and type of PRV.
The key is the Quality Plan that has the scope of inspection defined and agreed between buyer and seller.
Hope that answers.
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Per ISO-4126, only the term Safety Valve is used regardless of application or design.
