I have modeled my case using real air valve data. At one place it's showing large vapor volume. Surge is under the permissible limit.
Can a air valve handle this volume or what should I do to reduce the vapor volume ?
Air valve spec details also attached.
Model has add one 50mm dia double acting air valve at the pump house and 100mm dia. Triple acting air valves at about 250-300m, 800-850m, 1150m distances.
Looking forward to hearing from you.
Have you tried using the air-valves in the system? How much is the reduction in the vapor volume when air valves are used?
When using any surge protection equipment, the purpose of using it is to mitigate the transients produced in the system. Using the right equipment such as an air-valve or a surge tank depends on how effectively the transients are reduced in your system. Besides this, one should also consider the project cost of these equipment, available space and installation considering the project requirements.
The best way would be to try using several surge mitigation options such as using air-valves, surge tanks, hydropneumatic tanks etc. and check how each of these are effective in mitigating the transients produced.
Here are some informative articles which can help you;
Modeling Reference - Air Valves
Protective Equipment [FAQ]
Hope this helps.
Bentley Technical Support
If you are looking at time zero in the screenshot provided, this shows that there is a large negative pressure at the high point in question, even in the initial conditions. Would this actually happen in the real system, or would you have an air valve at the high point that would stay open in the initial conditions, with part-full/gravity flow in the downstream piping? If the latter, then the initial HGL at the high point would be zero and I would suggest modeling the high point as a Discharge To Atmosphere element, as there would be an air-gap there that the transient waves would not pass. See the following articles for more:
User Notification "Initial pressure less than vapor pressure. At the pipe end(s), the elevation(s) or head(s) are incorrect"
Modeling Reference - Discharge To Atmosphere
Otherwise - the volume shown in your first screenshot would be air volume, if it occurs at an air valve location. This can be expected in a case where the hydraulic grade falls below the air valve elevation, as air will be introduced. Whether or not the volume of air that you see is "acceptable" or not is based on your own judgment, but I would point out two things:
Jesse DringoliTechnical Support Manager, OpenFlows ProductsBentley Communities Site AdministratorBentley Systems, Inc.
Answer Verified By: Sushma Choure
Thank you for the reply. We have used 5000L surge tank at the start. I hope this would be the reason for the negative surge at the initiation. I will run the suggested scenarios by you.
Thank you for the reply. I have used the air valves in the system as well, but significant reduction in the vapor volume was not noticed. We have used 5000L surge tank at the pump house (0m chainage). I will try combination of surge mitigation measures as suggested by you.