The answer is, no, the nozzle load does not always have to be in the -Y direction. However, if it isn't, you better have a really good understanding of why it is +Y in your SUS case.

It's true that the nozzle itself doesn't care if the load is +Y or -Y (same for the other force and moments as well). If the vendor has been given a design load of X,Y, and Z lbs and MX, MY, and MZ ft-lbs, then signs should not really matter to the equipment at that point.

The point that you missed in the responses, Paldex, is that, if you are getting a +Y on a nozzle in your sustained case, it can be an indication of a poor support arrangement. If you disconnect that nozzle connection (or change the anchor restraint stiffness to 0), you are likely to see a +Y displacement at that node. If you see something like 1/16" of movement, you probably don't have a big concern. If you see the node lift a couple of inches when you disconnect the equipment anchor, you have a very poorly supported pipe system.

On the other hand, I've ended up numerous times with a +Y load on a pump discharge in particular where I have a spring over the discharge nozzle. When a hot pump system heats up, it's going to shift load from other supports to the nozzle. To compensate, I have on occasion set the spring load to higher than what Caesar calls for, resulting in a +Y load on the pump nozzle in SUS. The reason for this is that in OPE, the final -Y that ends up on the pump nozzle is still within the allowable range. So, this would be a case where I would expect to have a +Y load in the SUS case and not be concerned.

There is rarely such a thing as "Always" in our business.