1.5 Dampening

Figure 9

Figure 10

The most effective dampening of gas springs is achieved by using a restrictor type check valve piston, operating initially through the pressurized nitrogen gas and finally into the oil. Without dampening, rapid extension could occur with possible product failure, associated damage, and injury.

A schematic of an extension dampening system is shown right. The o-ring prevents flow around the outside of the piston. During compression, the valve disc and the o-ring are forced away from the orifice plate producing a large non-restrictive flow path for the fluid. At extension, friction on the o-ring forces the valve disc against the orifice plate and the fluid must now pass through a small orifice, slowing down the motion.

This design has only two moving parts, the o-ring and the valve disc, which shuttle to give large or minimal flow paths. When the valve disc shuttles to the free flow position, the orifice is flushed of any contaminants and is thus self-cleaning and non-clogging. Because of its short length it is also not temperature sensitive. (Other less effective dampening designs might use a labyrinth or maze, which is viscosity or temperature sensitive. Additonally, they are susceptible to blockage from contamination.)

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Extension Time

The typical extension time curve for an unloaded gas spring is shown at right. The first portion illustrates the rapid passage through nitrogen gas, followed by a slowdown through the oil.Typically, AVM gas springs have an extension velocity ranging from 1 to 3-inches per second. A rate of 3-inches per second translates to a 3 second extension time for a gas spring with a 9-inch stroke, 2 seconds for a 6-inch stroke, and 1 second for a 3-inch stroke.

Actual extension times should be based on what is most appropriate for the application, and should be established between AVM and the customer. AVMs design engineers can custom tune the extension characteristics to the customer's requirements.

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