Using Pressure Reducing Valves

My coworker Bill wrote this up, based on frequent requests for help with Pressure Reducing Valves:

There are two types of PRV valves, so there are two ways to handle the calculation:

Type 1 - Fixed PRV

Three calculations are required for a factory set or field adjustable PRV: Static at PRV, System Demand at PRV and Maximum Residual Pressure Available at PRV. Use those calculation results to determine which setting to use for the required flow demand.

Two HydraCALC Input files are required for each of those three calculations: Input file 1 – The sprinkler system to the PRV and Input file 2 - the PRV to the supply.

Refer to Fixed PRV Calculation.pdf for instructions

Type 2 - Auto-Adjusting PRV

A Cla-Val - Pressure Reducing Valve (there are other brands available) will automatically reduce a higher inlet pressure to a steady lower downstream pressure, regardless of changing flow rate and/or varying inlet pressure. You will need the manufacturer's material specification sheet for the valve you are using and enter the pressure loss for that valve.

The pressure loss for this type of PRV can be entered into HydraCALC as a fixed pressure loss. Refer to Auto-Adjusting PRV Calculation.pdf for instructions

Note:

If the PRV is located at a fire pump (Usually a Cla-Val type) the information can be entered into the HydraCALC pump curve. Enter the pressure limit (such as 175 psi max) and enter the PRV type and model in the “Regulated By” input field. The calculation process will take care of the PRV in the pump curve.

Comments

[George Ali Blackburn]

As pointed out by Tim D, in the end note regarding entering the pressure limit, it isn't made clear where to enter this information. You'll find the 'Outlet Pressure Limit' box in upper middle section of the Edit/Create Pump Curve window.

So when you're entering your pump information, you can set the max pressure value at the same time.