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Hello my name is ***** ***** I will assist you. So if you have backed a couple of turns the engine should start to come down by itself or with some pressure by hand. If it is not moving it looks like the valve has blocked and not allowing the piston to move up or down. Try light tapping while operating the pump with a mallet and see if it helps, if no then you would need to take the pump to a hydraulic specialist to have it checked.
If you require further assistance let me know,
It is the valve that lets the fluid go to the piston .