Pressure-relief valve with teflon seal

A pressure-relief valve for protection of hydraulic units in underground mining functionable against a sudden overload in pressure, comprising:

• a valve housing including an upper part and a connection piece;
• a valve spring lodged in said upper part;
• a valve piston arranged and longitudinally slidable within said connection piece, said valve piston being engageable forceably against said valve spring, said valve piston including a blind bore and radial bores, said radial bores being perpendicular to and communicating with said blind bore, and a pressure medium being flowable through said bores;
• at least one sealing ring arranged in said connection piece over which said piston travels, said sealing ring being positioned to correspond adjoiningly with said radial bores, and said sealing ring consisting of a very hard plastic material producing very low friction and having a rectangular cross section;
• and
• at least one annular groove within said connection piece receiving a respective said rectangular sealing ring, said at least one annular groove being defined by a groove bottom and a support wall perpendicular thereto with a bevel connecting said groove bottom and said support wall.