It is important to understand several key features of dampers before selecting the design that will work best in your application.
All dampers will increase resistance to movement of the shaft as the velocity increases. This requires that when you specify the resistance (load) required for you must also indicate the velocity of the shaft. The simplest way to identify this would be to specify a load say 20lbs and the time it will take to travel say 2 inches. So you would state a 20lb load, 2 inch travel in 2.5 seconds. Many customers will provide 2 speeds with the force required at each velocity, a typical graph showing force vs speed is shown below for multiple different force outputs available from AVM.
The critical item to damper functionality is how the design compensates for the increase in volume inside the tube as the shaft is compressed. Clearly if the damper was full of oil you could never compress the shaft because oil is non compressible and it has nowhere to go to make room for the shaft. This divides dampers into 2 broad categories – Cavitating and Non-Cavitating.
Cavitating Dampers – The damper is filled with a combination of oil and air. As the shaft is compressed it compresses the air an equal volume to allow movement. These work well vertically where the air and oil are separated by gravity but when mounted horizontally the air and oil mix creating inconsistent dampening rates.
Non-Cavitating dampers – In this design the air is prevented from mixing with the oil to ensure smooth operation regardless of how it is mounted. The separation of the air and oil is achieved in many different ways including air bags, closed cell foam, floating pistons to name a few.
AVM uses a floating piston design in the mono tube dampers and an air bag or foam in the dual tube (short non cavitating dampers). A more complete description is provided for each damper on their respective pages.