Background of the invention The present invention relates to a ball valve gasket according to the preamble of claim 1.

As it is known, in ball valves the ball shutter is tightly supported in the valve body, which is made by one or two pieces, by means of two opposite annular gaskets consisting of plastic, for example PTFE, and housed in seats provided in the valve body. On the side facing the ball shutter said gaskets are provided with a corresponding spherical rounding for obtaining a geometrical engagement with the associated ball shutter.

The sealing action is given by the compromise resulting from the gasket plastic elasticity on one hand and the pressure pushing said gasket against the shutter on the other hand.

As shown for example in the Figures 1 to 4 known gaskets for ball valves may have cross sections of different shapes having the common feature of being nonsymmetrical.

From an analysis it has been detect that this feature causes practically several disadvantages which are partially set forth as follows: A) First of all such asymmetric gaskets require an unambiguous assembling position, that is with the rounded side facing the ball shutter. This slows down an automatic assembling of said gaskets because the couple of gaskets to be inserted in a ball valve are to be inserted in two different positions. Self-acting gaskets loaders are to be designed with particular expedients.

In the case of a manually assembling the error of overturned gaskets may be rather frequent. Therefore, particular care is required in a correct positioning of both gaskets which likewise slows down the assembling time.

In both manually and automatic assembling if one or both gaskets are inserted in an overturned position this, if detected, requires a rather long re-positioning of the gaskets.

B) Due to the fact that the lateral gasket side facing the valve body is flat along the complete gasket height is completely pressed in its seat in the valve body or against an intermediate supporting element it is clear that under such conditions the gasket is not allowed to carry out any bending movement. This requires a very high pressure of the gaskets on the ball shutter in order to achieve the necessary sealing action. However, in turn, said strong pressure of said gaskets on the shutter causes a high twisting moment for the shutter opening/closing movements by means of the valve lever or the like.

This disadvantage becomes greater with the increasing of the ball shutter diameter and, generally, after long intervals between opening/closing rotations of the shutter.

C. The asymmetric cross-sections of the known gaskets necessarily require a rather great quantity of material which is due to the asymmetric design of said gaskets.

It would be desirable to need less material.

Summary of the invention Accordingly, the aim of the present invention is to provide ball valve gaskets which are not affected by the disadvantages of the prior arte gaskets and with the same ball shutter diameters allow to reduce the twisting moment which is required for carrying out closing/opening movements of the ball valve.

The stated aim is achieved with a ball valve gasket having the features set forth in claim 1.

Further advantageous configurations are inferable from the dependent claims.

With the teaching of the present invention several important advantages are achieved.

First of all the symmetric design of the gaskets avoids the need of an unambiguous positioning of both gaskets during the insertion thereof into a ball valve, that is during the valve assembling.

This will facilitate and speed up an automatic valve assembling.

Also the gasket loaders will have an easier design.

In the case of a manually valve assembling it will no more be necessary to pay attention to a defined positioning of the gaskets as the symmetric design of the gaskets will allow an"always correct" insertion of said gaskets into the valve body. Further, also the manually assembling will be carried out in a shorter time.

The symmetric design further requires less material on the gasket side facing the valve body and defines the configuration of an annular hollow space between the oblique segment on the external lateral side of the gaskets and the associated seat in the valve body, that is substantially in connection with the engagement between gasket and ball shutter. With these expedients the gaskets can carry out bending movements in longitudinal direction that is"to spring" in contrast with the resistance exerted by the shutter to be rotated so that when considering equal shutter diameters the twisting moment which is necessary to carry out the common valve opening/closing movements is substantially reduced, wherein an unobjectionable sealing action is always assured.

Secondly the less quantity of material required by the symmetric gasket design represents a smaller manufacturing cost of the proposed gaskets.

Yet another advantage of the gaskets according to the present invention is to be seen in the fact that the above mentioned advantages are achieved irrespective of the chosen material and the

dimensions of the gaskets as well as irrespective of the massive or hollow valve body.

Still another advantage is to be seen in the fact that the suggested gaskets can be directly used in the different types of valve bodies without requiring any modifications of said valve bodies so that the proposed gaskets can also be used in already existing and/or installed ball valve body.

Brief description of the drawings Further characteristics, advantages and details of the gaskets according to the present invention will become more apparent hereinafter from the following disclosure of some gaskets according to the invention which are schematically illustrated in the accompanying drawings where: Figure 1 is a frontal view of a prior art ball valve, partially shown in the middle longitudinal section; Figure 2 shows the detail A of Figure 1 in an enlarged scale; Figures 3,4 and 5 show a cross section across a prior art gasket, respectively; Figure 6 is a frontal view, partially in the middle longitudinal section as shown in Figure 1 of a valve provided with gaskets in accordance with the present invention; Figure 7 shows the detail B of Figure 6 in an enlarged scale; and Figures 8,9 and 10 show a cross section across a gasket in accordance with the present invention, respectively.

Description of the preferred embodiments Reference is first made to Figures 1 to 5 showing prior art gaskets.

From these Figure it is inferable that in a ball valve 1 having a valve body either in one piece or, as illustrated, in two pieces 3 and 4 the ball shutter 6 is tightly supported by means of two equal gaskets 7 and 8 having an asymmetric cross section. Said gaskets 7 and 8 are

housed in two L-shaped seats 9 and 10 obtained in the valve body 2, as illustrated, or in sleeve-like not shown inserts.

The ball shutter 6 has a throughgoing hole and may be rotated for 90° in both directions by means of a handle 12 having, in the shown example, the shape of a lever. 13 and 14 denote an inlet and outlet union, or vice versa, respectively.

The known gaskets 7 and 8, as well as the likewise known gaskets 15,16 and 17 of Figures 2 and 3 as well as 4 and 5 have different cross sections which have the common feature of being asymmetric.

The short dashes lines represents the ball shutter outline.

Using these gaskets the lateral side 18 thereof which is pressed against the associated seat 9 or 10 in the valve body is flat and abuts along its entire height against the radial side of said seats 9 or 10.

Therefore the prior art gaskets are not allowed to carry out any axial bending movement and may only carry out a moderate elastic deformation according to the features of the used plastic, for example PTFE, as already stated.

According to the present invention the gaskets 21, Figures 6 to 10, have a lateral side 19 cooperating with the seat 9 in the valve body 2 has an oblique segment 19A which is directed towards the gasket throughgoing hole 22.

In the same manner also The other lateral side 23 of the gasket 21 has a similar oblique segment 23A directed towards said gasket throughgoing hole 22.

According to the present invention both segments 19A and 23A have the same configuration so that the annular radially internal part 24 of the gasket 21 has the shape of an isosceles trapezoid. The annular radially external part 25 presents instead a cross section having the shape of a rectangle.

The angles ß defined between said oblique segments 19A, 23A and the lateral sides 19,23 are advantageously in the range between 10° and 30°, opportunely in the range between 15° and 25° and

preferably are 20°.

As an example, and using as gasket plastic PTFE, a gasket according to the present invention may have the following dimensions : - gasket thickness = 7 mm - external diameter = 125, 6 mm - internal diameter = 101, 6 - external diameter of the oblique segments = 110, 6 - angles = 20° - in a known manner, the external edges are smoothly rounded = 0, 5 mm x 45°.

According to the present invention the gaskets 21 may also have a radial recess 26 in the trapezoidal crown 24 (Figure 9) or a radial recess 27 in the rectangular crown 25 (Figure 10) in order to improve the elasticity characteristics of the gaskets 21.

During the ball valve assembling the symmetric gaskets 21 according to the invention can always be quickly and correctly introduced in consequence to the now possible positioning interchangeability, wherein with the same diameter with respect to a known gasket less plastic is also required.

As inferable in particular from the detail of figure 7, after insertion of the gaskets 21 into the valve 1 and the assembling thereof, between the oblique segments of the external lateral sides of the gaskets 21 and the associated seat 9,10 in the valve body 2 an hollow space 20 is formed.

Said hollow spaces 20 allow the annular trapezoidal crowns 24 of the gaskets 21 to carry out an elastic bending or flexion towards the associated seat 9,10 at the beginning of the opening/closing rotation of the shutter 6.

Due to this new axial springing possibility of the trapezoidal portion 24 of the symmetric gaskets together with the own elasticity of the used plastic it has been achieved the fact that the twisting moment

requested for carrying out the opening/closing rotations of the valve shutter 6 is substantially reduced with respect to known valves having the same diameter. If the angles ß increase also the elasticity of said trapezoidal portion 24 will increase.

The recesses 26 and 27 help to further reduce said twisting moment.

Even if reference has been made in particular to gaskets for ball valves it lies obviously in the spirit of the present invention to also adopt the teaching of the invention similarly for ball cocks, wherein said ball valves and cocks may be realized in any embodiment either as single valves or cocks or with incorporated components, like filters and so on.

From the above constructional and operating disclosure, it should be apparent that the gaskets according to the present invention efficiently achieve the indicated aim and the mentioned advantages.

In practicing the invention, one skilled in the art can perform geometrical modifications or variations, such as, for example, that of providing the oblique segments 19A and 23A rounded instead of rectilinear or of providing different shapes of the recesses 26 and 27 or of suggesting different suitable plastics possibly in the form of composites or laminates and so on, without departing from the scope of the invention.