Have you ever tried lifting the trunk lid(sometimes called "tailgate" or"boot" ) of your car with just one finger?How come you can lift a heavy piece of metal and glass with so little force?the answer ,if you didn't know already,lies in those clever piston-like hinges that support the lid either side.They're called gas springs(or gas dampers) and the make our lives a whole lot essier in all sorts of ways.

If you're sitting on an office chair right now,there's probably a gas spring underneath your body.Release the height lever and you'll feel (and probably hear) the gas in the spring being compressed ad the seat gently falls down.Gas springs have loads of other user too.Let's take a closer look at these handy gadgets and find out they work!

Why do we need gas spring？

Suppose there were no springs on the trunk lid of your car.It would be really heavy to lift,for one thing,There'd be nothing to hold it up in the air when you wanted to load in your shopping ,which would be a real nuisance.And if you let the lid go,it would crash down onto your car's bodywork,probably doing a lot of damage in the process.Now we could put a normal metal spring on the lid,but that wouldn't help so much.It would need to be very stiff and heavy spring,so it would take a huge amount of effort to lift the lid high in the air.The higher you lifted it ,the harder it would get to lift any further ,With the lid opened up fully ,the spring would be stretched out so much that it would pull straight back down again.

How a gas spring works

The basic idea

A gas spring is a bit like a super -sturdy verson of a bicycle pump,only it's filled with pressurized nitrogen gas (the major constituent of the air around us) and oil and completely sealed up so they can't  escape.The gas allows the spring to store energy,while the oil damps (slows and smooths) the movement of the piston and also provides Iubrication,Just like in a bicycle pump,there 's a tight-fitting piston mounted on a rod that can slide back and forth inside a cylinder (made from heavy gauge steel,not light plasticas in a bicycle pump).

Push on a gas spring and you force the piston rod and piston into the cylinder and this compress the gas.Stop pressing and let go and pressure of thr gas pushes the piston back out again.So far ,that sounds just like a bicycle pump- but it's working in a different way .Unlike with a bicycle pump.gas inside the cylinder can actually flow through or around the piston from one side to the other as it moves back and forward .Exactly how this happens varier from one design of gas spring to another ,usually the piston has one or more holes or valves in it.Now if the piston can move through the gas ,you might think it isn't compressing the gas at all.But don't forget that the whole cylinder is completely sealed.When the piston rod is inside the cylinder,it's taking up room that the gas previously occupied.In other words,when a gas spring is fully pushed in ,you 've compressed the gas inside by an amount equal to volume of the piston rod.If the piston rod occupies virtually the whole cylinder ,you can see that the gas is getting compressed quite substantially.The gas pressure can be very high,typically up to about 170 times normal astmospheric pressure. 

Wrote by Chris Woodford