i understand that the check valve catches the pressure from the Water hammer
that is correct
what i do not understand is why does the waste valve open (and close)
the water hammer opens and closes the waste valve (see bellow)
(and how does it sync with the check valve?)
it does not sync, (the waste valve opens and closes without relying on the check valve)
i guess it has to do with the air chamber (i do not exactly understand what is it for),
the air chamber is not for opening the waste valve but to capture as much of the pressure of the water hammer as possible
but i do not understand why does it open?
it opens because of low pressure caused by the water hammer (see bellow)
the way i understand that it works (hat tip to @BowlOfRed for helping me think)
that you create a perpetual water hammer using only one check valve (see below)
(i do not know exactly how it works and i see that it is possible to stop (videos of closed valve) and stopped valve)
and then you can just add a check valve with an air chamber for the pressure created by the water hammer a water hammer creates a bump of pressure to all go through it and not back to the water source since it is easier to compress the air then to go to the water source
how a perpetual water hammer works
see video 1 of diagram of the pressure of the water hammer and they bring an analogy of a train stopping video 2 (later in the video they explain the calculations) that after the stop it goes backwards
so if there is a check valve at the end of a pip (coming from a reservoir of water (which is higher then the valve))
1. check valve is open,
2. and it closes when the water goes through it at a certain speed,
3. it makes the water speed 0.
4. which creates a water hammer
5. which pushes the water back and (lowers the pressure).
6 which then opens the check valve
7. which lets the water out again
8. until it reaches the certain speed (then back to 2).
(for some reason (i do not fully understand yet) it can also not open even when the speed is 0 see the first 2 links (1 and 2))
from this video it seems that the size of the waste valve will not change anything
the reason why the valve can close is that the pressure of the water in the pipe (without the Water hammer) is enough for the valve to close,
so it should always be closed
what opens it is the very low pressure after the Water hammer as it can be seen in this video that after the Water hammer the pressure is so low that the water starts turning into gas,
but the reason the valve stays open until the amount of speed/pressure is reached that it should close is because of gravity (pulling on the flapper in the valve)