US Patent 6928681 Alternating pressure pads

An alternating pressure pad comprises at least two sets of inflatable cells, an air supply line to each set, a pump to circulate pressurized air through a circuit including the sets of cells and to return air from the cells to the pump, valve means for alternately causing inflation and deflation of each set, a sensor pad in the circuit through which pressurized air is passed and detecting means for detecting a reduction in air flow through the sensor pad to a level below a predetermined level and for increasing air pressure in the sets of cells to restore the air flow to a level above the predetermined level.