through a wide diameter hose 35 the pressure compensating valve may alternatively be connected to an air supply such as a compressed air cylinder 36 like a self contained breathing apparatus or alternativenly to an industrial pressurised air supply through a regulator 37 as shown in fig9 in this case a narrow diameter high pressure hose 38 connects the air cylinder to the regulator the regulator is in turn connected to valve through a wide diameter hose 35 as before the pressure compensating valve may also be connected to an air supply such as a compressed air cylinder 36 through a regulator 37 in a self contained breathing apparatus in this case two narrow diameter hoses 39 and 40 and connect the regulator with the valve one of the hoses acts as a pilot hose conveying to the regulator the pressure on the inlet side of valve it should be appreciated that the pressure compensating valve may be embodied in many other ways besides those described above for instance although all the embodiments show a valve having a generally circular configuration it could work equally well with other configurations such as oval or even square where a circular configuration is employed the surfaces need not be cylindrical but could be conical alternatively a linear configuration could be envisaged where the flexible barrier is straight and has a connection at either end to a hinge that lies parallel to its axis depending on the configuration the flexible barrier may roll stretch or deform as the two surfaces move relative to each other to open and occlude the fluid outlet it will be appreciated by persons skilled in the art that numerous variations and.