Piston for high-pressure hydraulic machine

In a hydraulic machine comprising in combination a cylinder and a piston in said cylinder, said piston comprising a body of bronze having a cylindrical outer surface and having at the periphery thereof an annular groove opening in the end face thereof which is subjected to high pressure, said groove being defined between a cylindrical inner surface and a truncated conical outer surface joined at the bottom by an annular surface which is semi-circular in cross section, said conical outer surface forming an angle not exceeding 6.degree. with the cylindrical outer surface of the piston, the piston between said cylindrical outer surface and said conical surface comprising a peripheral thin resiliently deformable flange having clearance with the cylinder of 1/100 mm. when undeformed but slidably engaging the cylinder when deformed outwardly by high pressure.