Want to get more life from your weed control sprayers? Don't push your equipment to its limits. Our experience is that techs run weed control power spray rigs at high speeds to get done quickly, and tend to overpressurize B&Gs and backpacks. All of these actions will reduce sprayer life.
Your power spray rig can run at extremes for short periods but it is not designed to be run full out all the time. Running "in the red" for extended periods will shorten engine and pump life. Make sure your techs know proper operating ranges. Ride along with them occasionally to verify.
If your backpack isn't spraying, don't pump it up more. You will break it. It is easy to turn a $3.00 o-ring replacement into a $50 repair. I like the following analogy for this situation. I went to France. The waiter didn't understand English, so I yelled louder. Don't overpressure your manual sprayers!