Instrument for indicating the length and number of decompression pauses in undersea diving

Claim 1

An instrument for indicating the depth and duration of the decompression pauses to be observed by an ascending diver of the kind including a deformable chamber subject to the external ambient ambient pressure and filled with liquid, said instrument comprising a hydraulic accumulator having an accumulator chamber defined at least in part by a movable member, resilient means loading said accumulator and having linear deformation characteristics from zero to a maximum value, a calibrated tube interconnecting said deformable chamber and said accumulator, the rate of displacement of fluid in either direction through said tube being determined by the ambient pressure acting on the deformable chamber and by the reaction of said resilient means loading the accumulator and indicator means having a graduated scale upon which the pressure in the accumulator is indicated, said pressure being proportional to the displacement of the movable member of said accumulator and therefore, to the volume of liquid displaced through said calibrated tube, said instrument further comprising a tubular body connected to said deformable chamber through said calibrated tube, a relatively slidable tubular sleeve having a transverse end wall closing one end and surrounding said tubular body to define therewith the hydraulic accumulator chamber, said transverse end wall constituting a movable index, a transparent casing enclosing said sleeve and provided with said graduated scale, said index being movable relative to said scale to indicate the pressure in said accumulator chamber, said resilient means comprising a helical spring under tension acting upon said sleeve and including respective helical grooves in the external surface of the sleeve and said tubular body, the ends of said spring engaging said helical grooves adjustably to permit regulation of the spring loading.