First of all, I am aware that restricted orifice inserts are not the recommended method for maintaining residual pressure below 100 psi in 1 1/2" hoses. However, a friend of mine is the Fire Technician at a hospital with over 700 of these restricted orifices installed. During a recent inspection, it was discovered that some of them were missing. He asked me what calculations would have been used during the original system design to determine the size of the orifice. My initial thoughts are that Bernoulli's Equation would be used because the increase in velocity caused by the restriction is resulting in lower pressure upstream of the restricted orifice (Conservation of Energy). Does anyone have experience designing systems that would have used this method? Again, the recommended scenario would be installing 1 1/2" Pressure Restricting Valves set as per the manufacturers' specifications. However, that is a very costly alternative compared to replacing the missing inserts from the original system design.
Any information is greatly appreciated. Thank you in advance.