The user experience for a product with a heavy lid or cover can range from awkward to annoying to downright dangerous.
Picture holding an industrial toolbox lid in place while reaching in one-handed, maybe twisting your back in the process. Or what if it comes down suddenly when your arm or fingers are in the way? The bruises won't be pretty, and the damage might be much worse.
This is why many designers add gas spring lid supports to their lid design. Others lean toward using counterbalance spring mechanisms or other mechanical spring solutions.
We use both in our motion control solutions -- here’s our comparison of the two approaches.
Note that this article is all about performance and safety, and less about cost. You can find that debate here.
Your Heavy-Duty Lid Support Options
Understanding the Gas Spring Mechanism
Gas springs, sometimes called gas cylinder springs, compression gas springs or gas struts, are used in many motion control applications.
They consist of a tube with an internal piston on the end of a rod or shaft. The tube is usually filled with nitrogen gas. A small opening in the piston dictates the rate at which it can move.
Understanding Mechanical Springs
This approach to hinge design (we call them hinges because they control the relative movement of two linked surfaces) uses coils to apply a specific rotational force. There is no gas involved, only good ol’-fashioned mechanics.
Considerations for Lid Lifts
Lids, doors, and covers are everywhere, and some of them present a pretty tricky design problem. Many of these applications require special motion control hinges or springs. For example:
- Centrifuges and other scientific equipment
- Tanning beds
- High-end refrigerators
- Food preparation equipment (i.e. French door ovens)
- Industrial toolboxes
- Medical equipment and storage cabinets
- Pharmaceutical manufacturing and storage equipment
In each case motion could be controlled -- for a while, at least -- by either mechanical springs or heavy-duty gas springs. However, once you consider the operational and environmental requirements, you'll see that there’s often only one long-term solution.
Six design goals to consider when specifying a spring or hinge are:
- Size & space
- Extreme-temperature applications
Here's a closer look at each.
Compression gas springs make a distinctive sound when operated, like a hissing snake. As long as you’re OK with that sound (and your customer base isn’t terrified of snakes), gas springs present no noise issue.
Engineers sometimes specify gas springs over mechanical springs because of their relatively silent operation.
Winner: Gas springs
When on their best behavior, gas springs offer a smoother ride for your lid or cover. However, the ultimate answer may depend on your cover’s range of motion.
Done well, a mechanical heavy-duty, spring-assisted hinges can give a steady motion over the whole range of movement. Gas springs don't always behave consistently along the entire range. Instead, you'll often experience a change in resistance throughout the travel, particularly at the end of the movement.
At best, users may find this disconcerting and assume the product is poor-quality. In a worst-case scenario, a bumpy ride with a gas spring could lead to a jolting stop and even product damage.
Gas cylinders have a critical weakness that makes them a poor choice for food and medical/pharmaceutical environments. This is the ever-present risk of leaks, which could contaminate food or medication. A poorly specified spring on a food prep table or blood draw station could result in a recall or even a lawsuit.
“Food-grade” substances can be used in gas springs to avoid contamination issues, but they jack up the price of the hinge.
Mechanical heavy-duty spring hinges do need greasing, but it’s nothing to worry about. This can be addressed through food-grade lubricants and will never have the same magnitude of impact as a cylinder leak.
Winner: Mechanical springs, by a lot
Size & Space
Designing for gas spring lid support means taking into account the length and mounting points of the struts. Gas springs typically need to span a greater percentage of the open/close point than mechanical springs do.
And don't overlook the need to avoid twisting, which may necessitate using a pair of springs.
Mechanical spring hinges offer equipment designers a wider choice of solutions. Springs can, for instance, be built into other springs. Additionally, your hinge manufacturer can often design them to conform to the space available.
That said, counterbalances are more bulky than gas springs and tend to be more difficult to hide in a design. It’s certainly not impossible to do, just a bit of a pain when aesthetics are important to your product.
When evaluating different types of hinges, safety is often a top priority, with ergonomics a close second.
Appropriately designed mechanical hinges let people of all sizes and strengths raise and lower equipment lids and covers without trouble. They will close at a safe rate so misplaced fingers don't get crushed and won't injure arms that get in the way as the lid is moving.
This is a surefire safety net for as many cycles as you wish to specify that the hinge lasts for.
Gas springs, not so much. Each time such a spring completes its job, it dies a little inside. The gradual loss of force can and will lead to the cylinder becoming useless if you don’t replace it in time. Even if your customer’s lid doesn’t get to that point, it still can become a hazard if the spring is lacking the force necessary to hold the lid up safely.
And we haven’t even touched on what happens in high-temperature applications ...
Winner: Mechanical springs, by a lot
The substances used in gas cylinders are highly temperature-sensitive, especially in extreme heat. The force it provides will change for the worse when very hot or cold. In extreme cold, gas springs lose force, hampering the performance of your lid. And when placed close to the heat of a grill or oven, you’re begging for an explosion.
In contrast, mechanical springs are essentially immune to the effects of extreme heat or cold. There are no gases in mechanical springs, nor any other substance that’s dangerous when paired with open flame.
Winner: Mechanical springs, by a lot
Heavy-Duty Lid Support Choice for You
The scores are in: Mechanical springs win by a landslide.
Gas springs have a purpose -- mostly in ergonomic products where safety is less of an issue. Many designers choose compression gas springs for motion control solely out of habit, and sometimes that’s OK. There are a lot of other applications, though, where engineers are installing gas springs and shouldn’t be.
Remember these final points:
- In general, reserve use of gas springs for low-cycle products with a light load.
- Any place you need to apply a force to neutralize a weight, or you are concerned about the environment affecting your hinge’s performance, counterbalancing is the safer route.
- You can actually combine gas and mechanical springs in a design with the help of your motion control solutions provider.
In many cases, counterbalance-style mechanical springs may offer you a competitive advantage. As always, let the needs of your application dictate your choice.
Want to start your counterbalance journey? Weber Knapp's new LiftGate Assistant Lid Calculator helps you get a jump start on your lift gate assist projects!
Editor's Note: The article was published in 2019 and has since been updated.