Valve closure hammer Effect

Hi collegues,

Greetings,

I would like to inquire about the closure of valve 2 or 3 which is an intermediate valve on a transmission line, hammer effect from various aspects:

1- Is it essential to study this valve closure effect in hammer.

2- Can the closure of this valve sudden closure and if what is the case that will cause this? 

3- Will the surge vessel contribute in the protection of the line after valve ?

4- Generally in water hammer simulation is valve closure modeled separately from pump failure or in combination?