The safety valve of most manual pumps is a non adjustable overflow valve set inside the pump head. Just to limit the maximum pressure. In actual use, the operator needs to look at the pressure gauge and press it slowly when the pressure is approaching.

Of course, it's OK to set an overflow valve at the outlet of the oil pump, but it's a little troublesome.

The maximum pressure output can be adjusted by adjusting the compression amount of the overflow valve plug at the outlet of the oil pump. Carefully try the corresponding pressure gauge several times to get the expected value.