Este texto en wikipedia las describe:"Valves whose disc is between the seat and the stem and where the stem moves in a direction into the valve to shut it are normally-seated or front seated. Valves whose seat is between the disc and the stem and where the stem moves in a direction out of the valve to shut it are reverse-seated or back seated. These terms don't apply to valves with no stem or valves using rotors" y pueden verse en el sitio web referido abajo, donde las nombran como válvulas de vástago ascendente