TZ50 emergency hand pump

my tz50 has a hydraulic hand pump on the hyd manifold with the solenoids for boom movements, used to move lift components up or down when the lift is inoperative/emergency. It does not do anything when i pump it. I removed it, and it has suction and seems to work when moved by hand. Hyd oil did not flow out the hole when i removed it. When i use the buttons on the ground control box, it makes the hand pump physically jump at the beginning, when any button is pushed, as if the manifold is being filled with oil as the pump feeds oil to the manifold, for whatever function you have pressed button for. I am thinking the manifold is not staying full of oil, letting the emergency pump do its job. Is there a check valve somewhere that is failing and allowing the hyd oil to drain from the manifold? The hand pump is at the top of the manifold, so if the manifold does not stay full, there is no oil for the pump to move.