Air spring cylinders offer an alternative to standard cylinders.
Sometimes called air-bags, these cylinders look nothing like the tube and end-cap type cylinder that is associated with the word ‘cylinder’.
Air springs are basically a fabric-reinforced rubber donut with a metal end plate at the top and bottom. As the air spring is pressurized the unit expands and the end plates move apart. As the air spring is vented, the end plates move towards each other.
The inherent flexibility of the rubber donut allows the air spring to be used in pivoting applications without the use of a clevis. They also allow a greater lateral or angular misalignment between the ends-plates than would be possible with conventional cylinders.
Due to their compact design air springs can offer high actuation forces in a relatively small package while also providing a very favourable stroke to retracted height ratio. As air springs contain no sliding seals, they have no breakaway friction, as traditional cylinders do.
Air springs need to be restrained upon extension to prevent an over-running load from pulling an end-plate from the cylinder. They also need to be supported on retraction. The load should not be allowed to settle down onto the cylinder as this could cause the end-plates to crush the rubber portion of the cylinder. A mechanical stop should be used to prevent this from occuring.
Although they are referred to as air springs, they are equally capable of extending and retracting under the pressure of water, nitrogen or ethylene glycol (antifreeze).
As the term ‘air spring’ suggests, they can also function as vibration isolators.
The spring rate of the unit is controlled by the air pressure within the air spring. This allows the same air spring to be used at all mounting points of equipment even though the equipment loading may not be even.
Vehicle Suspension Systems
Air springs are used extensively on bus and truck suspensions, an application ideally suited to the air spring. Clearly, an air spring used in a vehicle suspension is required to act as a vibration isolator. As load changes, the pressure within the air spring can be changed to compensate. When vehicle loading does not require as many wheels in contact with the road, the air spring can be retracted to raise the axle.
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