How it works

General

A gas spring consists of a steel cylinder containing gas under pressure and a rod which slides in and out of the cylinder through a sealed guide.

When the gas is compressed by the retraction of the rod, it produces a thrust in return, acting like a spring.

Compared to traditional mechanical springs (whether helicoidal, Belleville washers or rubber), the gas spring has an almost flat force curve, even for very long strokes. It is therefore used wherever a thrust is required that is in proportion to the weight to be lifted or moved, or to counter-balance the lifting of movable, heavy equipment.  

 

 
How gas springs work 

In its simplest version the gas spring consists of a cylindrical body (C) and a ground rod (S) called also stem, on the end of which a piston (P) is anchored, which accomplishes cycles in and out of the body (C) through a sealed guide (G). The body contains nitrogen gas under pressure (see arrows). When the rod enters the cylinder, the gas passes from below the piston (B) to the upper part (A) through channels made in the piston. By varying the cross section of the channels (F) the gas flow may be adjusted thereby slowing down the rod sliding speed to a certain extent.

 
Measurement Thrust 

The thrust of the spring is measured with a special dynamometer at a room temperature of approx. 20 °C with the rod compressed by about 10 mm and free from friction by the seal.

The measurement is given in N and is a “static” value normally referred to when defining the characteristics of a spring. Other components interact with this basic value and become especially noticeable in the “dynamic” phase of the spring. We are referring in particular to the friction produced by seals and rod supporting guides.

The resistance exerted by such friction acts in the opposite direction to the rod movement, it has a value of approx. 2/3 kg and is added to or subtracted from the above-mentioned “static” thrust.

The closing force is indicated in the graph by F0 and the opening force by F1.

It can be seen that F0 and F1 are higher and lower respectively than the average line which identifies the “static” thrust force (FM).

The thrust of a gas spring is determined by the pressure that the nitrogen in the cylindrical body exerts on the section of the rod. By suitably assembling rods of varying cross sections with bodies of suitable volume, by acting on the gas input pressure and adjusting the channels on the rod or by introducing a greater quantity of oil, various operating configurations of the gas spring may be obtained in addition to the required thrusts in order to satisfy a wide range of user requirements.