After removing air, the cushion should retain its hardness for three weeks. This is not a rule, clearly, and it depends on how you use the cushion. Unused (lying on a shelf), the hardness does not change over several months. With many spasms, or frequent changes of pressure and shape, air may need removing more frequently. It is recommended that the pump was always at hand, fastened to the frame of the wheelchair. If a hardened cushion doesn't maintain its hardness for 24 hours, it needs to be repaired.