Mechanical effect on the pump, you are operating at conditions that will not have guaranteed vibration levels, will not have been considered for motor sizing or NPSH requirements, and will not be covered by manufacturer's warranty in the event of premature wear or other damage.
Poorly worded for a few reasons, but most important is runout flow should be based on the % of pump's best efficiency point, not on the pump's rated flow. The assumption that these flows are going to be the same or very similar isn't always valid. That language will require a less than ideal selection (hypothetically, say rated point is 115% of BEP) to operate in a potentially dangerous (from a reliability standpoint) region of 1.15 x 1.2 = 1.38, 138%) of BEP. That can be a pretty tall order depending on pump type, and to meet that requirement may lead to excessive motor size, excessive NPSH requirements, and difficulty passing vibration during performance test.
Strictly speaking, it can't be both 110 and 120, because the requirement is 110 or 120."Or" can't include "and." If you posted this in the language forum, I would argue that meeting both (end of curve flow more than 120%, which is more than 110 AND more than 120) would not comply with the specification. If I asked for my car to be painted red or blue, I would not be happy if it ended up striped, polka dotted, or purple.
So, that spec puts the end of curve flow firmly between 110% and 120% of "rated flow" which is oddly specific and has little to no basis in reality. Unless your reality includes relying on a lot of assumptions being correct, and that reality is not engineering.
