Abstract: An underwater eardrum protector for use in underwater diving by a person having a perforated eardrum includes an inflatable bladder insertable in an ear canal of the person; a tube for supplying a non-compressible fluid to the bladder so as to inflate the same; a housing fluidly connecting the bladder to the tube; and a pump which supplies the non-compressible fluid to the tube, the pump including a cylinder having an inner wall, a piston slidable in the cylinder so as to define a variable volume chamber with the inner wall of the cylinder, the chamber being in fluid communication with the tube, O-rings connected with the piston for providing a fluid seal between the piston and the inner wall of the cylinder so as to seal the variable volume chamber, and a piston rod for slidably moving the piston in the cylinder so as to reduce the volume of the chamber and force the non-compressible fluid in the chamber through the tube and into the bladder, the piston rod being connected with the piston in a freely rotatab