Most tanks have air over a water bladder. This keeps the air from being absorbed by the water which finally would result in no air left in the tank to act as a spring to push the water out. Normally the air pressure precharge is set slightly below the cuton pressure
with no water in the tank. When the pump comes on the bag fills compressing the air around it. For max water delivery per fill cycle you want the precharge very near but
below the cuton pressure. When you raise the water pressure setting without raising the precharge you wont get as much water delivery between run cycles... but,
much worse, you may overfill the bag and burst it. In some tanks the bag can expand enuf to fill the tank and prevent this. Hope yours is that way, otherwise your horse washer may have popped your bag when he upped pressure to 100#.

larry