Hi there. I’m relatively new to WaterGEMS and having trouble with the automated Fire Flow analysis. I have made a network including tanks, pumps and many hydrants and I can run the Fire Flow analysis fine, getting correct answers. But I was wondering if it was possible to include the pressure losses I would expect to see in the hydrants. I need a residual pressure of 4 bar after the hydrant, with a loss of 1.7bar through the hydrant. Is there a way to include the losses in the hydrant? Thanks
What we call available fire flow is the amount of water that can be delivered to the node at the required residual pressure. This is the value that regulators and insurance people want to know.
If you want to account for the loss through the hydrant, you can increase the required residual by 1.7 bar. That value seems excessively high to me. That appears to be not just head loss through the hydrant but also the conversion of pressure head to velocity head.
The AWWA standard C502 for hydrants requires no more than 2 psi (1.5 m) of head loss through a hydrant at 500 gpm (32.5 L/s) for the 2.5 in outlet.
Answer Verified By: Sam Robson
This Wiki article supports Dr. Walski's comments above. And if you search for Fire Flow in our Communities Wiki articles, you will find many other articles which should help you with your Fire Flow Analysis.