# Reverse Suspension Spring

So, in a car either a liquid or a gas gets compressed when force is applied to the suspension, and when the force is removed the gas/liquid tries to expand again which makes an effect like a spring,

But could you make the opposite, or does it already exist? so a pull creates a vacuum (or just lower pressure), when the pull is stopped the vacuum (or just lower pressure) will try and pull back, and work like a spring?

edit:

While waiting for answers i googled a bit, and what Ι could find was something called gas springs, but these only seem to be for dampening and only suspension? or can they also be used for pull and retract like a normal steεl spring?

Thanks in advance for information. (:

• Liquids are generally not compressible.
– NMech
Jul 20, 2021 at 11:19
• Let me rephrase then (even though I know @SolarMike will probably find something to complain about), liquids generally in the context of dampeners are not considered compressible in the same manner as gasses.
– NMech
Jul 20, 2021 at 11:27

The problems with the vacuum would be that

1. the resulting force would always be less than 1bar times the cross-section.

In a typical dampener the pressure of the N2 (or compressed air) is a few bars, which results in a much more compact cross-section.

1. It is difficult to maintain a vacuum

Even if you could create a vacuum, it is very difficult to maintain it. Therefore in the long run the vacuum would drop and it would drop the force.

If the liquid (which is typically used for dampening) does come into contact with the vacuum, then the vapors from the liquid would reduce the vacuum pressure very quickly (let alone the air molecules which are in the liquid that would almost immediately go to the vacuum).

## double action hydraulic dampeners

If I understood correctly, i think what you are after are double action hydraulic dampeners. They come (generally) in two flavors

• Single tube.
• Twin tube

Figure: Single and twin tube shock absorbers.(source: wikipedia)

The working principle for tension and compression is shown in the following image:

Figure: Twin tube shock absorber (source: motorcyclespecs)

• Doesn't the oil create alot of resistance for the piston? i would like it to behave like a steal spring? Jul 20, 2021 at 11:35
• Oil is used primarily for the dampening and to transfer pressures - at least in double acting hydraulic dampeners. There are so many variations that you might find exceptions, but I can't think of any just know. Someone might help and provide a useful counterexample.
– NMech
Jul 20, 2021 at 11:38
• So what you are saying is you dont know if there exist gas springs that doesnt dampen? abit confused about your message Jul 20, 2021 at 11:41
• You can vary the orifices in order to tune the dampening characteristics. But an automotive dampener needs to have a good dampening response. Unless I misunderstood and you are not talking about automotive use.
– NMech
Jul 20, 2021 at 11:43
• not talking in automotive use, just an example, i want to hang a decently heavy load in a spring around 30kg and bounce it, you would need a pretty big steal spring for the spring not to break, so thought a gas spring might be better for higher load uses Jul 20, 2021 at 12:11

Most car suspensions are based on a spring - used to be flat cart type but now most cars have coil springs.

Some cars did go with a hydraulic suspension - early minis come to mind.

If you really mean the shock absorber, or damper, then they can be pressurized and tend to use oil.

Never seen a vacuum based system on trucks or cars but it might have been done - however, given how complicated it would be...

Edit: based on the addition, some things use high pressure nitrogen cylinders, or bags, to provide a spring-loaed action for hydraulic systems. One example is for hydraulic arms that need to move if they encounter an object but need to stay put otherwise. Some are over 400Bar so knowing what you are about to undo is crucial...

• Sooo i did some googling while waiting for an answer, and what im looking for is apperently called a gas spring, but they all seem to work by suspension, and not pull, or does they work both ways? Jul 20, 2021 at 10:22