Dave Diehl, Thanks for your valuable reply.

"If I was running a hammer load using a static equivalent, I would run it both positive and negative - if the system is nonlinear"

Means..

Case 1. positive and negative forces at a time, means in CAESAR-II both positive and negative forces in vector F1 only. and in next elbow both forces in vector F2 and so on ...

In load cases:

Check 1: F1, F2 and so on.. check individually with two forces acts on each elbow. and

check 2: F1 + F2 + F3 + .. case also considered. means at a time two forces are acting at all elbow in the entire piping system.

Case 2. Positive force in vector F1 and negative force in vector F2.

In load cases:

Check 1: F1, F2 and so on.. check individually with one force on each elbow

Check 2: F1 + F2 + F3+ .. case also considered. means at a time two individual forces are acting at all elbow in the entire piping system.

In both cases which one is correct method to safe the piping system in water hammer effect.