In nearly all slur studies for brass instruments, the author writes out each pattern for all seven valve combinations (or slide positions). This is to make sure the student gets mastery in the (relatively difficult) 1-2-3 valve combination as well as the easier open combination–and all of the combinations in between. At the same time, over-practice of slurs can be an issue. I would like to propose an easy alternative.
When a pattern is already learned, and the student is reviewing, why not play less valve combinations of an exercise–instead of all seven valve combinations, she could play only “open,” “1-2” and “1-2-3”? Three combinations, instead of seven, is a much more manageable and chop-saving approach. The student will still get the experience of the extremes of tubing length, but without nearly as much wear and tear on the embouchure.
Once a something is learned on the trumpet, it is often better to spend time on it for review periodically, but not to overwhelm physically with over-practice.