GB2105010A

GB2105010A - Sealing means for a ball valve

Info

Publication number: GB2105010A
Application number: GB08224148A
Authority: GB
Inventors: Costantino Vinciguerra
Original assignee: Nuovo Pignone SpA
Current assignee: Nuovo Pignone SpA
Priority date: 1981-09-02
Filing date: 1982-08-23
Publication date: 1983-03-16
Also published as: SE8204986D0; FR2512158A1; FR2512158B1; IT1138189B; JPS6182181U; IT8123730A0; CA1192889A; SE448908B; SE8204986L; DE3232565C2; JPS5846270A; CH651641A5; DE3232565A1

Abstract

The sealing means for hermetically sealing a shut-off ball valve or a gate valve, is constituted by an elastomeric gasket (6) of substantially triangular cross-section with rounded vertices and a curved base, and which is retained in a cavity (7), also of triangular cross-section, in an annular floating seat member (2) of the valve, by means of a metal retaining ring (8). <IMAGE>

Description

SPECIFICATION Annular sealing means for a shut-off ball valve or a gate valve This invention relates to an annular sealing means for a shut-off ball valve or a gate valve.

Sealing in a ball valve is known to be effected at the present time by means of an annular floating member having suitable cavities which respectively house a main annular gasket providing sealing towards the valve ball, and another annular gasket providing sealing towards the valve body. The annular floating member is urged towards the valve ball by a set of springs which keep the main annular gasket in contact with the ball, so providing a seal even when the pressure difference is zero, this seal becoming hermetic as the operating pressure increases, since such an increase generates a progressive additional load on the main gasket by a piston effect.

It is apparent that in order to obtain an effective hermetic seal, the main annular gasket should ideally be very soft and project considerably from its housing. In this respect, the softer the gasket and the more it projects, the more it is able to overcome any defects on the ball surface, due to constructional imperfections, scratches or incisions caused by foreign matter entrained by the operating fluid.

On the other hand, the fundamental problem arising in such valves when subjected to high pressure differences is the tendency of the main annular gasket to become extruded, i.e. to become dragged out of its housing, during the opening of such valves, by throttled fluid passing at high speed through the housing.

In the present state of the art, such main annular seal gaskets are constructed of a resilient material and have a circular crosssection. However, such a gasket obviously possesses none of the aforesaid characteristics necessary for providing an effective hermetic seal. In this respect, the fact that the gasket is of circular cross-section means that only a small proportion of it can project from the housing if the gasket is to be effectively retained within the housing. Again, in order to prevent extrusion it is necessary to use gaskets which instead of being soft are on the contrary rather rigid so that harmful contraction of the gasket cannot occur. Finally, a gasket of circular cross-section can rotate in its seat during the movement of the ball, resulting in possible deformation of the gasket and a consequent loss of the seal.

According to the present invention, there is provided an annular sealing means for a shutoff ball valve or a gate valve, the sealing means comprising an annular floating seal member in an annular cavity of which is housed an annular elastomeric seal gasket having a substantially triangular cross-section with rounded vertices and a curved base, said annular cavity, which is also of substantially triangular cross-section, being partially defined by a retention ring serving to retain the gasket in the cavity.

Thus, according to the invention, there is used an annular gasket of elastomer construction and having a cross-section which, instead of being circular, widens rearwards so that its escape from its housing is impossible, the gasket being retained in its seat by a retention ring, e.g. a metal retention ring. The gasket is substantially produced by joining, in a particular manner, a normal O-ring to another O-ring which has a much greater diameter than the former.

More specifically, the annular seal gasket is characterised by being formed from an elastomer and by having a substantially triangular cross-section with rounded vertices and a curved base, and which is retained in the annular cavity, which is also of triangular cross-section, by means of a metal retention ring supported by the annular floating member.

The annular sealing means according to the invention and the annular gasket thereof can be fitted to a gate valve as well as to a ball valve.

The invention will now be described, by way of example, with reference to the drawings in which: Figure 1 is a partial perspective view of a shut-off ball valve containing an annular sealing means according to the invention; Figure 2 is a section, to an enlarged scale, through that part of the valve of Fig. 1 in which the annular sealing means according to the invention is fitted; and Figure 3 is a section through the annular sealing means according to the invention, to a further enlarged scale.

In the Figures, there is shown a shut-off ball valve consisting of a valve body 1, a valve ball 3, and an annular floating seal member 2, the latter being disposed between the valve body 1 and the valve ball 3, and being resiliently urged by a circumferential set of springs 4 against the valve ball 3. The annular floating member 2 acts as a support for an annular gasket 5 forming a seal with the valve body 1, and for a main annular gasket 6 forming a hermetic seal with the valve ball 3, the latter gasket being housed in an annular cavity 7 of the floating member 2, and being retained therein by a metal retaining ring 8 which is also supported by the floating member 2 and which may be a split ring.

The main annular gasket 6 is of elastomer construction, and is formed substantially by joining (at least in theory if not in actual practice), in a particular manner, a normal 01 ring of radius r (see Fig. 3) to another O-ring having a radius R which is much greater than the former, so as to obtain a resultant cross section which widens rearwards. In short, the annular gasket 6 is in practice an elastomer of triangular cross-section with rounded vertices and a curved convex base 6'.

According to a preferred embodiment, the triangular cross-section of the annular gasket 6 is an isosceles triangle.

As can be seen, the annular seal gasket 6 does not rotate in its seat during the movement of the ball, is not subject to extrusion during any throttling of the operating fluid when the valve is partly open even though the gasket is constructed of soft material, projects from its seal such as to ensure a seal even against partly damaged surfaces of the ball, and is simple and easy to install. The shut-off ball valve can be fitted to large diameter pipelines, where it is subjected to high pressure differentials.

Claims

1. An annular sealing means for a shut-off ball valve or a gate valve, the sealing means comprising an annular floating seal member in an annular cavity of which is housed an annular elastomeric seal gasket having a substantially triangular cross-section with rounded vertices and a curved base, said annular cavity, which is also of substantially triangular cross-section, being partially defined by a retention ring serving to retain the gasket in the cavity.

2. An annular sealing means as claimed in claim 1, for a shut-off ball valve, including means for urging the sealing means towards the ball of the valve in use of the sealing means so that the annular gasket is pressed against the ball of the valve.

3. An annular sealing means as claimed in claim 1 or 2, wherein the cross-section of the annular gasket and the corresponding crosssection of the annular cavity are substantially in the form of an isosceles triangle.

4. A shut-off ball valve or a gate valve including an annular sealing means as claimed in claim 1, 2 or 3.

5. An annular sealing means as claimed in claim 1, substantially as hereinbefore described with reference to the drawings.

6. A shut-off ball valve as claimed in claim 4, substantially as hereinbefore described with reference to the drawings.