The City reviewer is asking for the Residual and Velocity pressures on the fire hydrants that I modelled for the site. I did find the "Pressure(Calculated Residual@Total Flow Needed)" in the flextables, but could not find anything saying Velocity Pressure. Please help.
Can I get some help on this please?
Hi Sayan, you had posted in a forum that is not intended for product technical support. I have moved your post to the OpenFlows community, which is the place to go for WaterCAD technical support.
Sayan Kundu said:Residual and Velocity pressures
Can you explain more what you mean by "velocity pressure"? Are you looking for the velocity of flow in the pipe adjacent to the hydrant at the available fireflow? If so, you would need to configure the auxiliary results section of the fireflow alternative and use the Fireflow Results Browser to view the velocity in the pipe. Meaning, click the respective hydrant in the list in the Results Browser (which causes the plan view and element properties to reflect what happened during that fire) then look at the velocity in the properties of the adjacent pipe (or annotate it and view the annotation in the plan view). See more here: Using the Fire Flow Results Browser to view hydraulic results during a fire flow in FlexTables and Properties
Velocity of flow out of the hydrant opening (as opposed to the adjacent pipe) is not something reported by the software, since the opening diameter is not an input field and typically users would not need to know this velocity (as the velocity would be lower in upstream pipes with diameter smaller than the hydrant opening,)
Also note that the "Pressure (Calculated Residual @ Total Flow Needed)" is one of several results calculated by the automated fireflow feature. You can read the following articles for more information on interpreting fireflow results:
Understanding Automated Fire Flow Results
How does the Automated Fire Flow analysis work?
If the reviewer is actually referring to flushing velocity, you'll want to look at the Flushing tool which looks at system velocities when a hydrant is simply opened (and flow is based on the system pressure and emitter coefficient). See more here: Conducting Flushing Studies in WaterGEMS and WaterCAD
If this does not help, please provide more information on what you're looking for.
Regards,
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
Hi Jesse, please see the reviewer's markups on the second page of the attached PDF file. He is asking what Pressure (Maximum) means in the table. I look forward to your help on this.
PDF
Hello Sayan,
In your fire flow alternative have you applied pressure residual lower limit as 20 psi? If yes then pressure (Calculated Residual) for hydrants is reported as 20 psi = residual pressure constraint, it means that the residual pressure constraint would be violated if any more flow was applied.
Please go through below wiki to understand more about the fire flow results.
About maximum pressure reported in the junction and hydrant flex tables, this pressure is for baseline steady state results for your model and not for fire flow results.
If you want to look at the fire flow results then please look at fire flow flex table.
Sushma Choure
Bentley Technical Suppport
Hi Sayan. It sounds to me that what the reviewer is wanting is "velocity head". This is simply v^2/2g (v = velocity, g= accel due to gravity).
I would also offer a word of caution when using the automated fire flow analysis. You should thoroughly research this and know exactly what WaterCad is telling you - it may not be giving you the information you think it is!
There have been several discussions in this forum regarding this very subject. I strongly urge you to read the several threads in this forum.
As it was explained to me, the automated fire flow results only give you an indication of what flow & pressure are available in the system near the hydrant, not what is being delivered by any particular hydrant.
If you want to know exactly what flow & pressure are available at a hydrant nozzle, you need to actually set up the hydrant as "open", then run an analysis. If you are using an EPS simulation there are a couple of additional steps you may need to take to set the system up so that it will run without generating a "system disconnected" error.
Good luck.