Annex E
(normative)
Verification of piston rod stability

E.1 Calculation of moment of inertia for piston rod cross-section

The moment of inertia of a solid piston rod’s cross-section is calculated according to formula (E.1):

      ………………(E.1)

The moment of inertia of a hollow piston rod’s cross-section is calculated according to formula (E.2):

     ………………(E.2)

E.2 Calculation of the radius of gyration of a piston rod cross-section

The radius of gyration of a solid piston rod’s cross-section is calculated according to formula (E.3):

      ………………(E.3)

The radius of gyration of a hollow piston rod’s cross-section is calculated according to formula (E.4):

      ………………(E.4)

E.3 Design of installation method and installation coefficient m

The installation coefficient m is determined according to the installation method described in Table E.1.

Table E.1

Installation method	Diagram	Installation coefficient m	Description
Hinge – hinge		1	Suitable for most gas springs
Fixed – free		1/4	Suitable for chair height adjustment gas spring
Fixed – hinge		2	Suitable for special situations

E.4 Calculation of permissible critical force

When the slenderness ratio is , the permissible critical force F_L is calculated according to formula (E.5):

   ………………(E.5)

When the slenderness ratio is , the permissible critical force F_L is calculated according to formula (E.6):

   ………………(E.6)

E.5 Verification of piston rod stability

The safety factor n of a piston rod stability is calculated according to formula (E.7):

       ………………(E.7)

The stability check of the gas spring piston rod is mainly to ensure that during the operation of the gas spring, the piston rod will not experience instability, thus guaranteeing the normal operation and safety of the gas spring. The above are the general steps for the stability check of the gas spring piston rod. In practical applications, factors such as the working environment of the gas spring, dynamic loads, and impact loads on the stability of the piston rod also need to be considered. If necessary, a safety factor can be introduced for a more accurate check.

Gas spring design calculation (English version of national strandard, initiated by LeiYan Gas Springs), proposed and prepared by SAC/TC 235 (National Technical Committee 235 on Spring of Standardization Administration of China).