What should I do if the hydraulic press of the groove press can’t go down?

Rst, turn on the hydraulic knob switch to raise the groove pressing wheel. Then place the pipe on the base of the groove pressing wheel, rest the other end of the pipe on the pipe support roller, and align and level the pipe with the groove presser. Next, tighten the hydraulic switch, turn on the power switch (which has forward and reverse directions), and then manually move the hydraulic rod up and down. (There is a scale indicator next to the hydraulic wheel).