Hello,
I have an existing model that I've been working in, created by a coworker a few months ago who is no longer at my organization.
My question is about surge relief valves. There is a calculation spreadsheet that I pulled off of this site earlier today that I've attached. Based on the results shown on here, I should be seeing 158 cfs released from the surge valve at this specific time.
In HAMMER however, this doesn't occur. Instead my peak flow from my SRV is about 3 cfs or 1.944 MGD at a 16" SRV connected to a 16" pipe.
Why is there a disconnect between this excel sheet and the model?
I know that in HAMMER you recommend using 150 lb/in as the spring constant. Why is that? I am just trying to ensure that this model is running correctly and properly conveying surge releases.
In order to look at this, it would be good to have a copy of the model as well, so we can see the input. There are two options for sharing your model files on BE Communities. If you would like the files to be visible to other members, compress the files into a zip file and upload them as an attachment using the ‘Advanced Reply editor’ before posting. If your data is confidential, you can follow the instructions in the link below to send it to us via Bentley Sharefile. Files uploaded to Sharefile can only be viewed by Bentley.
communities.bentley.com/.../bentleysecurefilesupload.aspx
Please let us know when the model files are uploaded.
For the spring constant value, this is a suggested value if you don't have something from the manufacturer. As this is not always available, this possible value is suggested for use. If you can obtain the actual value for this from the valve manufacturer, that would assure the best results.
Thank you.
Regards,
Scott Kampa
Bentley Technical Support
Scott - I just uploaded the file to your secure server. We don't have a manufacturer value.
I guess it's also worth mentioning that I ran the model several times with fluctuating SRV spring constants and saw little difference in flow results at the SRV, until I made the SRV spring constant very large (10,000 lb/in). Maybe after you see the model you'll know, but why would you see that little variability there but such a large amount of variability in the spreadsheet?
Hello Kara,
There are a few things you may want to consider. First, the spreadsheet that comes with the TechNote was updated a few months ago with some improvements to the calculations. You may want to download the spreadsheet again for use in the comparison. Here is a link to the surge valve TechNote: communities.bentley.com/.../modeling-reference-_2d00_-surge-valves.aspx
Second, the value that you are comparing the results to is actually the volume ("total discharge"). To view the actual discharge, you can add the surge valve as report points (in the transient calculation options) and look at a time history graph to see the results.
There are a couple of other issues that may need to be address. First, the discharge to atmosphere element D2A-2 appears to have a pressure drop and typical flow of zero. You will likely want to have some kind of value for these in order get results that are more reliable. You can find more on discharge to atmosphere elements at the following link: communities.bentley.com/.../modeling-reference-_2d00_-discharge-to-atmosphere.aspx.
Second, the time steps used in the calculations are quite large. You can see the time steps used by the program by going to Analysis > Transient Time Step Options. The result of the large time step is that many of the pipe lengths in your model are being adjusted quite a bit. A smaller time step may be a better option and something you might want to try in your testing. More about length adjustments can be found here: communities.bentley.com/.../9401.aspx. I will note that the SRV results are sensitive to the time steps/length adjustment.
I will continue to look into this to see if anything else can be found, particularly in relation to the SRV results when compared to the spreadsheet, but I wanted to get the above information to you.