By far the most common industrial lift is the hydraulic scissor lift table. This may seem like a complicated piece of equipment, but in actuality hydraulic lift tables are really very simple in design.
Hydraulic scissor lift tables are comprised of five major components:
- Platform – This is the top of the lift table where lifted product sits. It can be supplied in a variety of sizes.
- Base – This is the bottom of the structure that rests on the floor. It contains the track the scissor legs travel in.
- Scissor legs – These are the vertical members that allow the platform to change elevation.
- Hydraulic cylinder – The most common industrial scissors lifts are actuated by one, two, or three single-acting hydraulic cylinders. These allow the lift table to lift and lower.
- Motor or Power Source – Most hydraulic scissor lifts are powered by either an electric or air motor. These provide power to the hydraulic pump which actuates the lift table.
Hydraulic Lift Table Operation
A hydraulic lift table raises and lowers when hydraulic fluid is forced into or out of the hydraulic cylinder(s). As hydraulic fluid is forced into a cylinder, the cylinder strokes outward forcing the scissor legs apart.
Raising the Lift Table
Since one end of both the inner and outer legs are connected to the base and platform, the platform rises vertically as the scissors legs open. The free end of the scissors legs are fitted with rollers that run in the base.
Any time a lift table is raised, it is being supported by a column of fluid. The lift table remains in a raised position because the fluid is held in the cylinder(s) by a simple check valve.
A lift table’s up speed is a function of the hydraulic pump and the motor that is turning it. The desired up speed and capacity to be lifted determine the amount of work the motor has to do, thus the horsepower required. If a lift table needs to move faster, it will take more horsepower. If a lift table has to have greater capacity, it will also take more horsepower.
Lowering the Lift Table
The lift table is lowered by opening a down valve that allows fluid out of the cylinder at a controlled rate. This down valve is solenoid operated and a “normally closed” type valve, which means it stays closed until the electric solenoid is actuated. This feature prevents the lift table from lowering if there were a power failure. When the solenoid opens the down valve, the fluid returns to the reservoir.
The down speed of a lift table is a function of controlling how fast the fluid is allowed to leave the cylinder. This is done with a flow control (FC) valve. The FC valve is pressure compensated, which means it regulates the flow to a predetermined range whether the lift is loaded or empty. These FC valves are fixed rate or non-adjustable and typically the lift table’s down speed is matched to lift table’s up speed.
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Tags: ergonomics, Lift Tables, scissor lift table