Valve tray

Mass transfer equipment comprises a base (3) having at least one riser (1) with inwardly and upwardly elongated sloping sides and a moveable valve cap (2) positioned above the riser (1), having outwardly and downwardly elongated sloping sides. Legs (5) extend downwardly from the valve cap (2) and possess stops which limit the movement of the valve cap (2) to such an extent that the lower edge of the sloping side of the valve cap (2) is never above the upper edge of the sloping side of the riser (1). Dimples (4) may be provided on the riser (1) to prevent sticking when the valve is closed.