DIAGNOSIS That's called "spitting" or "chugging," and it usually means there's too much water in the canner. Excess water boils up into the vent port where the weight sits, causing it to rock violently and spit liquid instead of maintaining a clean, steady steam release.
FIX For your 23-quart model, you only need 2 to 3 inches of water in the bottom to start. That's about 3 quarts maximum. 1) Let the canner cool and open it. 2) Pour out the excess water until you're down to that 2-3 inch level. 3) When you restart, make sure you're using a steady, medium-high heat—not the highest setting on your burner. Bringing it up to pressure too fast can also cause the water to boil up violently.
IF THAT DIDN'T WORK Check that you're using the correct weight for your target pressure. The 15 PSI weight has three separate pressure options (5, 10, 15 PSI). Make sure it's seated squarely on the vent pipe and that you've selected the correct pressure by aligning the right number with the stem.
HEADS UP Spitting can leave mineral deposits or food particles in the vent pipe, which can eventually clog it. After cooling, always remove the weight and the little vent pipe cover (if your model has one) and rinse them out to keep that steam path clear.