By David Liang
Now we can make a better suggestions for choosing the right air valve to prevent any mis-using and got troubles.
1.We tested and found that if we have a much bigger holes at the bottom of the cage, it is more easily to have blow shut with large quantity air exhausting like VAG- bigger holes on the cage bottom, and we do find optimization hole areas for less water coming out of valve body and no blow shut problem up to from dn 50-100MM, this needs lots of test and optimized a good solution.
2.No doubt for long transmission pipeline, there are many big projects in water transmission, lots of air valve failed specially if sudden pump power failure, the water hammer pressure will always 3-4 times of pumping head even the pumping is 3-4 bars, the hammer will come up to 9-12 bars, in such a case, the outflow water capacity is extremely high and the air valve can not be closed properly and had big leakage without stopping, they showed me some movie ( sorry, I don’t have the movie, but I did saw DN300 big leakage, main pipeline is 2600MM) even in America they have the same problem, and that is why anti shock device ( slow closing device ) is developed.
3. What China do Today, all those for transmission pipeline system should add
3-1. America way-by adding a silent check valve with 4 holes on the disc app. 15% of flow area to lower down ( look into the below picture- USA Val-matic & APCO ).
3-2. European way- by adding anti shock device on the top of the bonnet ( look into the below picture-CSA Italy )
( AFC makes the antic device similar to European design, new model number KARA )
4.In some other areas like the distribution system if there has any potential water column separation, we should use anti shock device to keep the system in a safety operation.
5.As a matter of fact that those who build the air valves should meet those problem too, it is not the valve problem, you have to
6.get a right way to face this problem.
7.This type of water hammer will always cause extremely high water flow speed out of valve and hold the float in the bottom area and prohibited from flowing up to close position or direct damage or collapse the float, this was happened in many cases.
8.The ocisillating and water column separation will continue couple times and take many seconds to calm down.