Here we explain how a hydraulic lift table works: from the lifting movement, to holding the load, to the lowering movement.
Even though we will explain how it works on a hydraulic scissor lift table, the principle applies to all lift tables. The only difference between the different types is the drive unit that is used.
To make the descriptions more understandable, you will also find a section from the hydraulic diagram of a simple lift table in addition to my explanations. I have marked the path that the hydraulic oil follows during the different phases in the diagram.
The lifting movement starts when the electric motor is turned on. The electric motor drives a small gear pump that feeds the oil from the tank into the hydraulic circuit of the lift table.
The gear pump is connected to the cylinders of the lift table via the hydraulic hoses. This allows the oil to flow directly from the hydraulic pump to the hydraulic cylinders. The oil flowing in now ensures that the piston rod extends from the cylinder barrel (active components = red).
As one end of the cylinder is connected to the inside scissors and the other end to the outside scissors, the scissors also move apart with the cylinders to raise the platform and so the load to be lifted.
When the desired lifting position is reached, check valves ensure that the hydraulic oil remains in the cylinders. Because the oil cannot flow from the cylinders back into the tank, the lift table remains in its current position.
I highlighted the main check valve in red in the hydraulic diagram. As you can see in the hydraulic diagram, there is also a check valve (green) in the path of the lowering valve, so that the oil must remain in the cylinders.
Hydraulic scissor lifts usually do not need the drive for the lowering movement. Instead, the dead weight of the platform is sufficient to allow the cylinders to retract.
To do this, the lowering valve is opened (see adjacent diagram). This clears the way for the hydraulic oil to flow from the cylinders back into the tank. As the oil flows out, the cylinders can retract again and the platform lowers with the load.
To prevent the lowering speed of the lift table from becoming too fast, a lowering brake valve is installed in the hydraulic line. This limits the maximum flow rate and to prevent the desired lowering speed from being exceeded.