Original question is whether WNC case is required for nozzle checking or not. In my previous post where I was comparing the results of the two attached files, what I was pointing to was: With Sustained result and operating result the trend is already clear. In sustained case full weight of the content is present. At that condition already upward force is acting. Now it is obvious what will happen when all weight is removed or weight is partially removed. It will cause even more upward force. That means the WNC case for nozzle checking was not required if with proper routing and locating the spring, a suitable spring was selected. Why select a wrong spring which can overturn the vessel with higher spring load . Then check with WNC case to find out the load is more!!! That is, it could have forces downward in both sustained and operating cases in this example. So that the difference could have been reduced. So that the upward force could have reduced when the content is removed. So that when content is not there no unwanted upward force occure. Otherwise any number of load case can be created and checked as one wish. Any multiplier can be applied on load cases. But I prefer to reduce the load cases to the minimum and try to understand the result by comparing the basic simple load cases.