Such a valve forms part of, for example, medico-surgical drainage systems where the valve can be operated by the user/carrier.

With a view to user comfort it is essential that the valve is completely tight when it is to prevent a flow from the inlet to the outlet as well as at the ends of the opening in the valve box serving as the bearing of the shut-off device.

In order to achieve this, according to the present invention it is suggested that at opposite ends the cylindrical opening in the box is provided with an outward facing conical surface designed to interact with a corresponding conical surface on the shut-off device where the shut-off device is embedded by means of a process and/or of a material causing the shut-off device to shrink more than the box upon cooling and causing cross sections of the box opening to deviate from a circular form in such a way that the extent of the shut-off device at right angles to the passage is slightly larger than in the direction of the passage.

When the shut-off device shrinks upon cooling, its conical surfaces will be pressed against the corresponding surfaces in the cylindrical opening, thereby achieving a particularly good sealing at the ends of the opening. Because of the deviation from the circular form, the shut-off device embedded in the opening does not have circular cross sections either, but in its closed position is pressed tightly against the orifices of the inlet and outlet in the box opening to prevent leakage along the exterior of the shut-off device.

The invention will be explained in further detail below in connection with the drawing where Figure 1 shows a sectional view of the axis of the cylindrical opening in a valve according to the invention; Figure 2 shows a sectional view of the valve at right angles to the axis of the opening with the valve open; and Figure 3 shows the same, but with the valve closed.

The valve shown on the drawing includes a plastic-moulded box 1 with an inlet 2 and an outlet 3 and an essentially cylindrical opening 4. In this opening, a rotary shut-off device 5 of plastic is embedded, which in the first position (Figure 3) prevents a flow from the inlet 2 to the outlet 3, but in the second position (Figure 2) allows a flow via a passage 6 in the shut-off device.

As appears from Figure 1, at opposite ends the cylindrical opening 4 has an outward-facing conical surface 7 which is designed to interact with a corresponding conical bearing surface on the shut-off device 5.

During manufacturing, the shut-off device 5 is embedded in the cylindrical opening 4 by means of such a method and/or of such a material that upon cooling the shut-off device shrinks more than the box 1, see Figures 1 and 2. This causes the bearing surfaces of the shut-off device 5 to be pressed against the outward-facing conical surfaces 7 in the opening 4 to the effect that they are tight-fitting (see Figure 1) and that when the valve is open, the shut-off device 5 does not fill the opening 4 along its circumference (see Figure 2).

However, cross sections of the box 1 opening 4 deviate from a circular form to such an extent that the extent of the shut-off device 5 at right angles to the passage 6 is slightly larger than in the direction of the passage.

A comparison between Figures 2 and 4 shows that because of the deviation from a circular form, the shut-off device 5 embedded in the opening 4 does not have circular cross sections either, but in the closed position is pressed tightly against the orifices of the inlet 2 and the outlet 3 in the box opening 4 to prevent leakage along the exterior of the shut-off device.