Please advise me if, I can use the following equation for calculating steam hammer forces at down stream of a stop valve, we use this approach in calculating steam hammer forces at up-stream of a stop valve and that seems correct to me:

F=(DLF) x K x m x a

Where:

m= mass flow rate of steam; a= speed of sound
DLF = 2
K= (pipe length/valve closure time x speed of sound) if length is less than critical length otherwise it’s equal to 1

What worries me is that, perhaps the pressure at the downstream of valve may reduce to zero (vacuum) as the valve shuts down. As such the pressure difference between the adjacent elbows of the run would be same as operating pressure of pipe and steam hammer force might be calculated as:

F= (DLF) x K x (operating Pressure) x (Cross sectional area of pipe)

Both these approch will give very different results