Hydrants/Monitors Residual pressure of 700 KPAg(100psig) for refinery process area.

Question

Hi, I have question in regards to minimum residual pressure. The fire water systems that we're designing required to meet the flow rate and residual pressure requirements at each piece of fire protection equipment at certain scenarios. The minimum residual pressure for my hydrants and monitor are 700 kpag (100 psig). The watercad calculation results always shows a failed constraint when I applied this residual pressure to a fire equipment @ certain scenarios. I think I made a mistake on my input or missed some. The design are for refinery process areas. I greatly appreciate any help . Thanks"

Tom Walski · Accepted Answer

If you are not providing sufficient pressure at a node, there are essentially two reasons 
 
1. The node is at too high of an elevation 
2. There is too much head loss between the source (an elevated tank or a pump discharge) and the node. 
 
It is best to think about this in terms of hydraulic grade line (HGL). Check the required HGL at the nodes that fail and determine if the HGL at the source is adequate and where there may be bottlenecks in the system.

Jesse Dringoli · Answer

It sounds like you're using the automated fireflow feature. To help understand the results and why constraints may fail, you might also find the below article useful: 
 Understanding Automated Fire Flow Results 
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