Instead of a compressive force, it would work in a tensioning force (like an elastic), so you can imagine how different it would be installed on the vehicle.

The idea is that the liquid - inside an apparatus similar to a shock absorber - would be in a vacuum, like a tendon, the vacuum on the liquid would pull the liquid apart creating a resistance (I think). You could have another reservoir of liquid connected so to control its flux through a orifice/s, similar to how a shock absorber does.

If there is a very simple term for that, I don't know. I tried to search for it, and only conventional shock absorbers appears. If such apparatus is even practical/efficient, I don't know, thus why I'm looking for it. hello

  • How would this device be used? You're looking for it to draw instead of push the piston? Commented Aug 22, 2022 at 13:35
  • @Pᴀᴜʟsᴛᴇʀ2 Yes, where would it be used? Well, I don't know, I want to know if it exists first so I can look it up...
    – Fulano
    Commented Aug 22, 2022 at 14:34

2 Answers 2


What you propose is possible in theory but impractical in practice.

When using a compressed gas, say nitrogen which is commonly used in shocks and such, the limit of pressure is the lesser of the point at which the gas liquifies or the structural integrity of the unit itself. But in practice pressure of 1000 psi or more are common. This allows for relatively compact designs.

The problem with using a vacuum, which certainly could be done is that you're limited to the difference between the vacuum you can produce and ambient pressure. So at sea level that is 14.7 psi. Even if you could pull a perfect vacuum, which you cannot, you would never be able to achieve more than 14.7 psi of working pressure. So any such design would have to be much larger to produce the forces needed to to the job.

Why is that? Well keep in mind that the force generated by a pressure differential is based on the area that it's working on. So if you have a 1000 psi difference and a 1 square-inch area, you can get 1000 lbs. of force. But to get that same 1000 lbs. force with a vacuum and it's 14.7 psi differential, you would need 68 sq-in of area. Fitting 68 sq-in. into a shock absorber sized unit would be a difficult engineering problem.


If the only thing you are wanting to do for some type of shock device to pull rather than to push, the simple solution is not to use vacuum, but instead, push from the other direction. Shocks are designed to push out (extend the rod). This is done with (IIRC) nitrogen gas. To get it to retract, it would just need to be designed with the gas to be introduced on the other side of the piston, which would cause it to retract. Not that I'm aware this type of "shock" exists at current.

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