If your hydraulic pump is not building pressure, the first thing you should do is check the fluid level and make sure it is at the correct level. If the fluid level is low, you should add more fluid to the system. You should also check for any leaks in the system, as these can cause air to enter the hydraulic fluid, which can reduce the ability of the pump to build pressure.
Another potential cause of this issue is a clogged or damaged suction line. The suction line is responsible for drawing fluid into the pump, so if it is clogged or damaged, the pump may not be able to build enough pressure to operate the system. If you suspect that the suction line is the cause of the problem, you may need to clean or replace it.
If the pump itself is worn or damaged, it may not be able to build enough pressure to operate the system. In this case, you will need to replace the pump.
Finally, if the relief valve is faulty, it may not be allowing the pump to build enough pressure to operate the system. In this case, you will need to replace the relief valve.
Overall, there are a few potential causes of a hydraulic pump not building pressure, and the appropriate solution will depend on the specific issue you are experiencing. It is important to diagnose the problem accurately and take appropriate action to fix it, as a faulty hydraulic pump can cause serious problems in your hydraulic system.