Lift struts are elegant and ingenious but so is the planned obsolescence from the manufacturer's view. Quickly rejuvenate them rather than throw them out.
--------------------------------------------Math Example------------------------------------------------
If P1=400psi=2757902.8N/M^2 and Area A=38.48 10^-6 M^2 (7mm arm cross-section)
F=PA=106.124N
Weight=F/G=10.818kg or ~23.8lb. G=9.81M/S^2.
If the volume of the spring is conveniently cut in half when the arm is all the way in, then we have PV=constant so P1V1=P2V2 and
At V1 the spring supports 10.818kg. Sufficient for a light tailgate. It's that simple.
At V2 the spring supports 2 x 10.818kg.
Charging a spring with 7mm cross-section arm to 400psi will support 10.8kg. If the arm cross section increases to 10mm then 400psi supports (10/7)^2 times as much.
