By using a spring tensioning system on the band blade the spring acts as a cushion as the blade expands and retracts. During the cutting process the round molecules that make up steel will flatten out under the cutting load. This is what is referred to as "shock".

The spring absorbs this shock since it has the ability to expand and retract with the blade. A hydraulic system does not have this ability and therefore is not as forgiving to the blade. The spring system is by far superior to hydraulic tensioning.