The dynamic event look so :
At beginn you become a high pressure on the valve.
This pressure (phigh)are higher as on the next elbow so you have a delta p in this pipe segment.
phigh can calculated with joukowski formula.
The pressure wave to travel in the pipe until the source.
Maybe on the source you can become to beginn this event a vacuum.
This vacuum collaps at this time pressure wave come to the sourge.
So the pressure wave go return to the valve and so forth...
until damping ( friction etc..)the pressure wave reduced at zero.

Calculation Methods :
1. Static with DLF = 2
2. Response
3. Time Historie
Normaly this 3 Methods to consider once pressure wave (vale to source)and not consider forwards and backwards pressure waves.
This szenario can to escalate the pipe with i higher dyn. result.

Sorry my english is from 1970.