Pressure Reducing Valve are commonly used to prevent excess pressure upon systems when supplies exceed the NFPA limit of 175 psi.
There has been much discussion regarding the 'application' of these valves when hydraulic calculations are being provided to the discharge of the PRV and determining the pressure margin available.
Currently, we have been instructed to calculate the system back to the PRV, use the PRV's friction loss calculator to determine friction loss through the valve and subtract that from the outlet setting to establish outlet pressure. This is then used as the available pressure at the outlet; minus the demand and you're left with the margin.
I'm not sure that I agree that the valves 'friction' loss need to be considered unless you are at a point where the PRV can no longer provide the set pressure (when the supply is unable to provide sufficient inlet pressure to overcome the internal friction loss).
Are there any 'papers' written for direction or other sources anyone might recommend?
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