I created a model from the field conditions that has two pressure zones (High and Low), these zones are separate for PRVs and pipes closed, each zone has its own tank and pumps (wells) that provide the flow. But, when I applied a fire flow analysis of 3hr- @1750gpm (that is supposed to work), the pumps can't deliver the head.
The node is in the high-pressure zone near the tank.
Hell Brian,
Pump cant deliver flow or head means that pump was trying to operate at the shutoff point (zero flow) or the pump would have to add more head to the system than is specified in the shutoff head, in order to elevate the water up to the downstream boundary condition. Or it is not able to deliver the extra fire flow added.
Check if other pumps are adding too much, so the pump in question is cannot overcome it.
Here is a list to check few things here, mentioned in wiki below.
User Notification "Pump cannot deliver flow or head"
If that doesn't help, we will need to see a copy of the model files to look into this.
Regards,
Sushma Choure
Bentley Technical Suppport
Hello Sushma,
I sent the copy of our model files through this link (https://communities.bentley.com/p/secure_file_upload), as confidential files. The file name is Bentley_PRA Water CAD-Copy-To be Reviewed.zip.
I couldn't fix our model. I tried each step that said these two forums, and nothing works!
https://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/9025/user-notification-pump-cannot-deliver-flow-or-head
https://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/10830/troubleshooting-negative-pressures-at-pumps-junctions-other-node-elements
Note: we are working with the scenario named "AverageDaily2019_Base updated:111219_ 1500 GPM Fire Flow @J-1406 for 2 hrs". When I applied the fire flow scenario for the J-1406 during the 2 hr of fire flow (or lower flow or lower duration), these notifications continue to shown:
Also, the pipes P-1833(1) and P-2114(2) are closed. The Tank-1 can't deliver flow and head, and the whole high-pressure zone is in negative pressures.
Thanks for your support,
Brian
Hello Brian,
The pattern you have set for fire flow is to provide fire flow at J-1406 between 18.00 hrs to 20.00 hrs, after computing the model you will observe that due to increased fire flow demand pumps need to deliver more flow than its maximum capacity hence you see the notification at 19.00 hrs about pump not able to provide the required flow for these 2 hrs. E.g. Max. flow capacity of PMP-5 is 200 gpm but in graph below more than 200 gpm flow is to be delivered by PMP-5. Same applies to PMP-7 as well.
So if on field pumps are delivering the fire flow as expected then please check your input data.
About P-1833(1) and P-2114(2) being closed, P-1833(1) is pipe adjacent to tank T-1, when the tank becomes empty or closed the adjacent pipe closes. Tank T-1 becomes empty and full almost every 4 hours, so you should recheck the controls on tank and how pumps are responding here. Controls should be set in such a way that tank neither becomes empty nor full.
Pipe P-2114(2) is adjacent to FCV, there are controls on FCV based on tank R-1 levels and FCV is working as per the controls.
Answer Verified By: BRIAN BINNEY
Thanks Sushma!
We had a mistake in the minimum elevation of the tank. The Model is fixed!