Hydrant Pressures during MDD

Question

Hello, 
 My boss is currently having me run a scenario on Max day settings on a street by opening 1 hydrant at a time. He wants the pressure to drop to 20psi when testing and currently the pressure is sitting around the high 50s and low 60s (psi). Is there a way to force the hydrant to go down to 20 psi? 
 
 I am very new to watergems so the more simple the explanation the better. 
 Thank you

Scott Kampa · Accepted Answer

Hello Alan, 
 WaterGEMS is a demand-based program, meaning that the demands will be satisfied and the other results are basically solved based on this demand. What is happening here appears to be that the demand at the hydrant you are opening never gets high enough to drop the pressure to 20 psi. 
 However, there is nice tool in WaterGEMS that should allow you to get the results you are looking for. Using automated fire flow, the program will basically run a series of steady state analysese, applying demands to junctions and/or hydrants in your model one at a time. The program will basically apply an additional demand to the nodes until either a threshold pressure (often around 20 psi) is reached or until a maximum fire flow is applied to the node. 
 I would recommend taking a look at the following link: Understanding automated fire flow results . This walks through the general setup for the fire flow run as well as how to interpret the results. Using automated fire flow would allow see an increased demand until you get to a 20 psi limit. 
 Regards, 
 Scott

Jesse Dringoli · Answer

I concur that automated fire flow may be what you're looking for. 
 Note that if you want to see the fireflow available at a node, when the pressure is exactly equal to 20 psi, another option would be to: 
 1) Right click on the hydrant, choose hydrant flow curve , 
 2) Set the nominal hydrant flow to 20 psi, 
 3) Compute 
 4) Look at the flow at 20 psi in the Data tab 
 5) Repeat for the next hydrant. 
 However, automated fireflow has the advantage of being able to consider pressure at other places in the network, which may drop to undesirable levels with the residual pressure is at 20 psi. In addition to the resources that Scott linked to, below is a video on our YouTube channel: