The question of whether a lift table can remain in any position can be answered with a simple "Yes" — at least in theory. However, this limitation makes it necessary to examine the topic more closely.
Why can a hydraulic lift table theoretically always stop?
To answer this question, let's take a look at a scissor lift table with the simplest hydraulic setup. The following components are of interest:
- Electric motor with an attached hydraulic pump
- Check valve
- Lowering valve
As long as there are no additional features in the hydraulic circuit (e.g. locking valves directly at the cylinder), the functionality can be explained as follows:
Lifting movement of the scissor lift table
When the electric motor is started, the hydraulic pump begins to pump oil from the tank towards the cylinders. The hydraulic oil generates pressure within the cylinders, causing them to extend. This extension of the cylinders results in the lifting of the lift table platform.
Standstill
As soon as the electric motor stops, the check valve and the lowering valve ensure that the hydraulic oil remains in the cylinders and cannot flow back into the tank. This keeps the platform in its current position.
Lowering movement of the scissor lift table
As soon as the lowering valve is activated, the path for the hydraulic oil from the cylinder back to the tank is opened. The weight of the scissor lift table now ensures that the hydraulic oil is pushed back into the tank through the lowering brake valve. This allows the platform to lower in a controlled manner.
In the neutral state, meaning when neither the lowering valve is opened nor the electric motor is running, the scissor lift table remains stationary regardless of the current position of the platform. This behavior allows for setting individual working heights, especially with work lift tables.
Why is the answer: "In theory, yes"?
The answer “in theory, yes” refers to the fact that a hydraulic lift table can essentially remain stationary in any position. However, practical experience shows that this is not always or permanently the case. Especially when holding the position depends solely on a single valve, it can happen that the lift table slowly lowers over time.
A common reason for the unintentional lowering of the platform is contamination within the hydraulic system. Fine dirt particles can accumulate at the lowering valve, preventing it from fully closing. As a result, the platform experiences a slight downward movement.
This phenomenon is already considered in the safety standards for scissor lift tables. A lowering of the platform by up to 5 millimeters within 10 minutes under the rated load is deemed acceptable.
However, this does not mean that maintaining an exact position with a hydraulic lifting device is impossible. With additional measures such as:
- Mechanical support devices
- Electronic position control systems
hydraulic lift tables can be kept precisely in their position for extended periods.
Comments (0)
No comments found!