Information about Gas Springs and their Application

How to calculate the F1 force required

 

Calculating the force required for a gas spring in an application is best done with a 

computer and a piece of software such as GASSIM. However, understanding how 

the calculation is done is a valuable piece of information to possess. If you know 

the factors involved in the calculation you are better able to understand how to 

adjust the mounting points when using GASSIM to gain the desired results. In order 

to calculate the force required by hand, it requires calculating the force at one position.

Then you must move the door to a new position and calculate the force required 

again. If you move the door 10 degrees or so and calculate the force required at every 

position, you can get an idea of what force is needed. The basic formula is.

 

           W x GM

F1 =   -------------   + (10-15%)

            SM x n

 

F1 = Spring force required

W = Weight of door

GM =  Gravity moment

SM = Spring moment

n = number of springs to be used

 

The formula will calculate the spring force required to balance the door. The 10-15% added will insure the spring will have not only enough force to balance the door, but will have enough force to actually lift the door. This method is not nearly as accurate as using a software package such as GASSIM, but it can be used to size springs into an application. Some of these values are fixed, such as door weight and gravity moment. You can adjust gas spring force, but you can also adjust the spring moment. This is probably the most important component in this calculation. If, for example, your design holds the door open to your satisfaction, but the door will not stay closed under it's own weight, then reducing spring F1 is most likely not the answer. By the time you get the F1 force low enough that the door will stay closed under it's own weight, then it most likely will not hold open sufficiently. In such a case, instead of lowering the F1 force, it is better to reduce the spring moment when the door is closed, but not when it is open. Then the door will stay shut under it's own weight, while still managing to hold the door open properly.