Tension springs, also known as extension springs, apply a resistive force as the spring extends and are commonly utilised to move or return a component part. Tension springs normally have special ends to allow application of the load (e.g. chest expanders) and these ends can be manufactured in a variety of shapes and sizes.
The design of tension springs is virtually the same as for compression springs, the formulae for load and stress being identical.
Tension springs, however, are different in two ways. Firstly, they are normally close-coiled whereas in compression springs the coils are open. Secondly, initial tension can be put into tension springs so that a particular load has to be applied to the spring before the coils begin to open.
Tension springs are available in a variety of different forms which are commonly used in many household products such as garage door assemblies, trampolines and white goods.