AIR VAVLES

Question

If I used VACUUM BREAKER to protect My pipe from negative Protection Due to Pump Shut Down ...
How can i know the Amount Of Air what entered the pipe ??
And How Can i KNOW that this amount of Air has got out from my Pipe and can it get out through the other combination air valves on the pipe ??
And is there a practical number for the amount of vacuum breaker i can use in the line in case of its length dint exceed 2000 m without making the system unstable ?

Sushma Choure · Answer

Hello Ali, 
 If you look at the time-histories graph of pipe connecting upstream junction and air valve you will see the air entered into the system. 
 
 You can use the "vacuum breaker" air valve type to model an air valve that allows air into the system but does not release it. However, it will not model the movement of that air pocket (in other words you cannot see it being swept downstream) See more on limitations here . 
 See more about the vacuum breaker air valve here and its limitations: Modeling Reference - Air Valves 
 In case of vacuum breaker, you will see the air volume change as the air pocket is compressed, but the mass of air in the pipe doesn't reduce. 
 Any air pocket left in the system due to a vacuum breaker valve is assumed to be expelled out of the system by some other means. 
 About practical number of vacuum breaker valves to be used in system, it would depend upon your purpose of using it and the output expected and your engineering judgement. There is probably a very limited number of applications for this type valve. However, it could be used for a draining pipeline. To see the impact of it you can model multiple scenarios with different combinations and choose the one which gives more stable results.

Jesse Dringoli · Answer

To add to Sushma's reply - you may need to look at the air volume time history graph for both sides of the air valve, as the air pocket can sometimes be shown on one or both sides. To see the total air pocket volume over time, enter a number in the "report period" field in the air valve properties, re-compute the transient simulation, then look at the table of details at the end of the Transient Analysis Detailed Report (from the Report > Transient Reports menu). This is mentioned in the "Reporting" section of the air valve modeling reference article that Sushma had mentioned. 
 Additionally, here is an article on comparing multiple transient protection strategies using scenarios and alternatives: Viewing HAMMER results for multiple scenarios 
 In most cases air valves are already present at local high points in order to bleed out air that accumulates in the system during normal operation, and these devices often supplement other transient protection devices and strategies in order to protect the system during events such as an emergency pump shutdown.