The hydraulic lock is a hydraulically controlled one-way valve with a relatively simple structure.

In forward direction, oil flow passes directly through the one-way valve. When reverse direction, the oil flow is blocked by the one-way valve. Control oil must enter the lower end of the control plunger, the plunger rises, and the one-way valve is opened, so that the oil flow can return.

The balance valve is a combination of a one-way valve and an externally controlled relief valve (which can also be understood as a hydraulically controlled two-position two-way valve), and has a complicated structure.

In forward direction, oil flow passes directly through the one-way valve. When reversing, it is also necessary to control the oil to enter the control port of the relief valve, open the relief valve, and return the oil flow. But if there is no external oil control, when the oil pressure rises to the opening pressure of the relief valve, the oil flow can also return.

So the most fundamental difference is that the hydraulic lock has no external control oil and cannot be opened no matter what. The balance valve can open itself when the pressure exceeds the set pressure.