The H-Factor

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.

You can find a document for this named Fixed PRV Calculation.pdf in your \HES\HydraCALC\Ver50\Docs folder

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. You can find a document for this named Auto-Adjusting PRV Calculation.pdf in your \HES\HydraCALC\Ver50\Docs folder

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.