The clever scissor lift mechanism allows these workhorse machines to safely raise workers to height.
Scissor lifts are mobile elevating work platforms (MEWPs) capable of lifting workers and their tools to height. They are compact in design, simple to operate and easy to move. How does a scissor lift work, exactly? Read on to learn about the components of these popular machines and the scissor lift mechanism that enables their up-and-down movement.
Scissor lift mechanism: The X factor
No matter the power source, all scissor lifts rely on a pantograph, or parallelogram, design. Steel support beams, sometimes called scissor legs, are arranged in stacked X patterns, with hinge pins at each intersection. When cylinders attached to a set of beams are filled with hydraulic fluid or compressed air, the rods exert upward pressure on the outer edge of the higher beam. This forces the X patterns to elongate, pushing up the attached platform. As the Xs elongate, the base narrows.
When the operator uses a button on the control box or joystick to lower the lift, the pressure in the cylinders is gradually released, the X patterns contract, the base widens, and the platform descends.
The speed of ascent and descent and the maximum lift height depend partly on how the scissor lift is powered. Generally speaking, electric scissor lifts are more compact and have lower maximum lift heights, while gas and diesel models reach the greatest heights.
Scissor lift components
Here’s a quick look at the main parts of a scissor lift.
The platform, also known as the lift table, holds workers and their tools and serves as the workspace. To help prevent falls, most scissor lift platforms include guardrails.
The base frame supports the rest of the scissor lift. Made of rigid metal, it has tracks to guide rollers at the bottom of the scissor legs, which allow the bottom legs to open and close. Together, the base and rollers help ensure a steady ascent and descent.
These crisscrossed steel beams connect the platform to the base. The longer the legs or, the greater the number of legs, the higher the platform can rise.
Scissor lifts have anywhere from one to four cylinders attached to one or more sets of legs. Depending on the type of scissor lift, the cylinders can be filled with hydraulic fluid or compressed air. When the cylinder is filled, the rod pushes outward, putting upward pressure on a leg and raising the platform.
The down valve, which is connected to the power supply, opens when the operator uses the controls to lower the platform. The opening of the down valve allows the hydraulic fluid or compressed air to leave the cylinder, which lowers the platform.
Flow control valve
The flow control valve controls how fast the hydraulic fluid or compressed air leaves the cylinder and how fast it enters. This regulates the speed of the platform’s descent and ascent.
The control panel features an interface that allows the operator to turn on the lift, set the speed and lift and lower the platform. These panels typically include an emergency stop button to be used in the event of a valve malfunction.
The scissor lift’s unique scissor lift mechanism allows these lifts to raise workers to areas at height despite the small footprint that makes them convenient to store. Their simplicity, compact design and ease of use make scissor lifts one of the most popular types of aerial lifts on any jobsite. Whether you’re working indoors or outdoors on a small or large project, the right scissor lift can help you complete at-height tasks safely and efficiently.