Low cavitation ball valve

Abstract

A ball valve (1) has a valve body (10) with an inlet port (11) and an outlet port (12), whereby a rotatable valve member (20) in the form of a spherical body with an aperture, especially a through hole (23), is arranged in the valve body (10) for controlling a flow of a liquid from the inlet port (11) along a flow path (F) of the ball valve (1) to the outlet port (12), whereby at a downstream side (22) of the valve member (20), there is an aperture (30, 30', 30'') in the flow path (F) for generating a pressure drop in a liquid flowing along the flow path (F), whereby: a) The aperture (30, 30', 30'') comprises a fluid passage with a hollow tapered section (33, 33', 33''), which is configured such that a cross-sectional area of the flow path (F) decreases from an initial cross-sectional area (35, 35', 35'') at an upstream end (31, 31', 31'') of the aperture (30, 30', 30'') in an intended direction of flow of the liquid to a minimum cross-sectional area (36, 36', 36'') of the flow path (F) at the downstream end (32, 32', 32'') of the hollow tapered section (33, 33', 33''); and b) downstream the minimum cross-sectional area (36, 36', 36''), the cross-sectional area of the flow path (F) increases to an enlarged cross-sectional area (37, 37', 37''), whereby the enlarged cross-sectional area (37, 37', 37'') downstream the aperture (30, 30', 30'') is larger than the initial cross-sectional area (35, 35', 35'') at the upstream end (31, 31', 31'') of the aperture (30, 30', 30'').

Description

[0001] Low cavitation ball valve

[0002] Technical field

[0003] The invention relates to a ball valve having a valve body with an inlet port and an outlet port, whereby a rotatable valve member in the form of a spherical body with an aperture, especially a through hole, is arranged in the valve body for controlling a flow of a liquid from the inlet port along a flow path of the ball valve to the outlet port. Furthermore, the invention is concerned with a HVAC system comprising such a ball valve. Other aspects of the present invention are directed to an aperture for use in a ball valve and the use of an aperture for reducing or avoiding cavitation and / or flow noise in a ball valve.

[0004] Background art

[0005] A ball valve is a valve that controls the flow of a fluid, i.e. a liquid or gas, by means of a ball having a bore, which is mounted in a rotatable manner in a housing between a valve inlet and a valve outlet. By rotating the ball, for example with a handle, a fluid path can be opened or blocked to control the flow of fluid through the valve. Ball valves typically are performing well after many cycles, have a long service life and provide a reliable sealing over the life span, even after long periods of disuse.

[0006] US 4,071 ,220 A (Kitazawa) describes for example a ball valve including coupled outer casing elements adapted to enclose a rotationally movable valve body having an axial flow passageway therethrough. The ball valve is intended to be mounted in a pipeline system for purposes such as opening, closing and conversion of a fluid flow path. The fluid flow path may be under a hydraulic pressure as in various pipelines, or it may be under high gas pressure, such as steam. The specific design of the valve allows for improving the maneuverability of the valve, and the operating shaft is maintained free from leakage and the closure function is assured even when a sudden variation of the inner pressure and melting of the seal members under a high temperature as in a fire occur.

[0007] However, ball valves are known for bad cavitation performance. Cavitation is the process of vaporization, bubble generation and bubble implosion which occurs in a flowing liquid as a result of a decrease and subsequent increase in local pressure. Cavitation will occur if the local pressure decreases to some point below the saturated vapor pressure of the liquid and subsequent recovery above the saturated vapor pressure. Especially in valves, cavitation may cause a great deal of noise, vibrations or even damage. This is in particular disturbing if the valves are used in residential or industrial buildings, e.g. as components of heating, ventilation, or air conditioning (HVAC) systems or as components of industrial plants.

[0008] With regard to cavitation, globe valves are known to be advantageous compared to ball valve. Globe valves comprise movable plugs or disc elements and a stationary ring seat in a generally spherical body. In order to improve cavitation performance, globe valves may be designed such that the flow is split into parallel flows. Also, it is known to divide the pressure drop into several (serial) steps. However, such kind of valves usually are rather large and expensive.

[0009] Thus, there is still a need to develop improved valves that do not have the disadvantages mentioned above or have them to a lesser extent.

[0010] Summary of the invention

[0011] It is the object of the invention to provide an improved valve. Preferably, the valve should have a good cavitation performance and low noise level, preferably over the whole operating range from fully closed to open. Furthermore, the ball valve should be compact in design and as simple as possible to produce.

[0012] The solution of the invention is specified by the features of claim 1. Accordingly, the inventive ball valve has a valve body with an inlet port and an outlet port, whereby a rotatable valve member in the form of a spherical body with an aperture, especially a through hole, is arranged in the valve body for controlling a flow of a liquid from the inlet port along a flow path of the ball valve to the outlet port. Thereby, at a downstream side of the valve member, there is an aperture in the flow path for generating a pressure drop in a liquid flowing along the flow path, whereby: a) The aperture comprises a fluid passage with a hollow tapered section, which is configured such that a cross-sectional area of the flow path decreases from an initial cross-sectional area at an upstream end of the aperture in an intended direction of flow of the liquid to a minimum cross-sectional area of the flow path at the downstream end of the hollow tapered section; and b) downstream the minimum cross-sectional area, the cross-sectional area of the flow path increases to an enlarged cross-sectional area, whereby the enlarged cross-sectional area downstream the aperture is larger than the initial cross-sectional area at the upstream end of the aperture.

[0013] Surprisingly, it was found that with the inventive aperture it is possible to reduce cavitation and flow noise essentially over the whole operational range of the valve. Without wishing to be bound by theory, it is believed that this is due to the special structural design of the aperture with a tapered section reducing the cross-sectional area of the flow path to a minimum cross-sectional area, and the subsequent increase of the cross-section to realize an enlarged cross-sectional area, which is larger than the cross-sectional area at the upstream end of the aperture.

[0014] Furthermore, the aperture can be easily installed or realized at a downstream side of the valve member without significantly enlarging the overall size of the ball valve. Especially, it is possible to provide the aperture in the form of a retrofit part for conventional ball valves. Alternatively, the ball valve can be produced with the aperture in the form of an integral part. Thus, the inventive solution allows for producing ball valves with improved cavitation and flow noise performance that are compact in design and quite simple to produce.

[0015] Especially, the inventive ball valve works for low as well as for high flow coefficients, i.e. cvor / (^values. The flow coefficient of a valve is a relative measure of its efficiency at allowing fluid flow. It describes the relationship between the pressure drop across a valve and the corresponding flow rate. Specifically, the flow coefficient / ( can be expressed as:

[0016] Thereby, Q is the flow rate (e.g. in m3 / h), p is the density of the fluid (e.g. in kg / m3), p0is the density of the fluid for the / Rvalue (e.g. TOGO kg / m3) and AP is the pressure drop (in bar) across the valve.

[0017] Especially, the ball valve is configured such that the cavitation factor z is > 0.45. This in particular across the complete operating range from a fully closed state to fully open state and with water as flow media. The cavitation factor zis defined as follows:

[0018] Thereby, 1 is the pressure before the valve, pT. is the pressure after the valve, pv is the vapour pressure of the liquid flowing through the valve.

[0019] Especially, an absolute value of the increase of the cross-sectional area downstream the minimum cross-sectional area is larger than an absolute value of the decrease of the cross- sectional area in the tapered section. This allows for further improving cavitation and flow noise performance. However, for example for special applications, other configurations might be suitable as well.

[0020] According to a highly preferred embodiment, in an intended flow direction, the cross- sectional area of the flow path continuously decreases at least in a subsection of the hollow tapered section. Most preferably, the cross-sectional area of the flow path continuously decreases over the whole length of the hollow tapered section. In this case, at least a subsection of the hollow tapered section forms a smooth transition from a larger crosssection to a smaller cross-section. Without wishing to be bound by theory, it is believed that this helps to reduce turbulences in the liquid flowing through the ball valve.

[0021] Especially, at least in the continuously decreasing subsection of the hollow tapered section, in particular over the whole length of the hollow tapered section, every point of a boundary surface defining the flow path in the subsection or in the whole hollow tapered section, an angle of inclination of an imaginary tangent plane in said point, with respect to an intended flow direction, is at least 3°, especially 3 - 25°, in particular 4 - 10°, highly preferred 4 - 6°. This makes it possible to improve cavitation and reduce flow noise particularly well.

[0022] However, it is also possible that in an intended flow direction, the cross-sectional area of the flow path, at least in a subsection of the hollow tapered section, especially over the whole length of the hollow tapered section, decreases stepwise in at least two or more steps.

[0023] Furthermore, a combination of a first section with as stepwise decrease of the cross- sectional area and a second and continuously decreasing subsection, or vice versa, is possible as well. This might be advantageous for special applications.

[0024] In particular, a transition from the minimum cross-sectional area to the enlarged cross- sectional area is a single step-like transition. A step-like transition is meant to be an abrupt increase in the cross-sectional area of the flow path. Such a transition is particularly effective for achieving the inventive advantages and at the same time easy to implement.

[0025] However, according to another preferred embedment, downstream the minimum cross- sectional area, the aperture comprises an expanding section, which, at least in a subsection or over the whole expanding section, is configured such that a cross-sectional area of the flow path continuously increases, especially from the minimum cross-sectional area to the enlarged cross-sectional area.

[0026] Thereby, preferably, at least in the subsection, especially in the whole expanding section, in every point of a boundary surface defining the flow path in the continuously increasing subsection of the expanding section or the whole expanding section, an angle of inclination of an imaginary tangent plane in said point, with respect to a in intended flow direction, is at least 45°, especially at least 80°. For example, the angle of inclination can be >90°, e.g. to produce an undercut. However, preferably the angle of inclination is < 90°.

[0027] For example, the expanding section of the aperture has a has a frustum shaped form, in particular a truncated cone shaped form, especially a truncated circular cone shape form. Thereby, an opening angle of the truncated cone in particular is at least 45°, especially at least 80°.

[0028] Especially, measured in an intended direction of flow, a length of the tapered section is larger than a length of the expanding section. This turned out to be highly beneficial for efficiently improving cavitation performance and for reducing flow noise.

[0029] For example, the length of the tapered section of the aperture is at least 150%, especially at least 300%, in particular at least 500%, of the length of the expanding section of the aperture.

[0030] However, for special applications and / or valve designs, other configurations might be suitable as well.

[0031] Especially, an edge radius of an edge of the aperture defining the minimum cross-sectional area is at most 4%, especially at most 2%, in particular at most 1%, of a maximum diameter of the minimum cross-sectional area. In case of a non-circular minimum cross-sectional area, the diameter is meant to be the diameter of a circle with the same area as the noncircular minimum cross-sectional area.

[0032] Preferably, the passage in the tapered section of the aperture has a frustum shaped form, in particular a right frustum shaped form.

[0033] Especially, the hollow tapered section of the aperture has a truncated cone shaped form, especially a truncated circular cone shape form. Thereby, an opening angle of the truncated cone in particular is at least 3°, especially 3 - 25°, in particular 4 - 10°, highly preferred 4 - 6°. Such apertures are easy to manufacture and give rise to a good cavitation performance and flow noise reduction.

[0034] The aperture is meant to be a passage to pass liquid through.

[0035] Especially preferred, the aperture of the spherical body is a through hole in the spherical body. Thereby, in particular, the through hole at least in sections fully surrounded by the spherical body. A through hole can in particular be produced by drilling a hole through the spherical body. However, in another preferred embodiment, the aperture is configured as a groove in the spherical body. In this case, in particular, the aperture forms a channel in the spherical body that is open on one side along the whole length of the channel. A groove can e.g. be produced by cutting into the spherical body from the side.

[0036] Especially, the valve member is a sphere with an aperture, especially a through hole, in particular a sphere with a cylindrical through hole running along a diameter line of the sphere.

[0037] Preferably, the ball valve is configured such that the flow path is a straight line.

[0038] Especially, the ball valve is configured such that a liquid flowing through the ball valve is not split-up in parallel partial flows.

[0039] Overall, these configurations ensure compact design, high flow capacity and low turbulences in combination with the further inventive advantages of the ball valve.

[0040] In particular, in an intended flow direction, the aperture, especially the through hole, in the rotatable valve member has a constant cross-sectional area, especially a circular cross- sectional area.

[0041] In particular, the flow path in the ball valve has a circular cross-sectional area, especially along the whole flow path. Valves with such cross-sections are particularly easy to manufacture and beneficial with regard to the inventive advantages.

[0042] However, at least section-wise or along the whole flow path of the valve, other crosssections, e.g. elliptical cross-sections, are possible as well.

[0043] Preferably, a cross-sectional area of the aperture, especially the through hole, defining the flow path in the rotatable valve member is essentially identical to the initial cross-sectional area of the aperture. Thereby, a smooth transition between valve member and aperture can be realized. However, other configurations are possible as well.

[0044] In particular, the aperture is a cylindrical body within the valve body. Especially, a distance between the upstream end of the aperture and the downstream end of the valve member is smaller than a length of the flow path in the valve member, especially the distance is at most 25% of this length, in particular at most 10% of this length.

[0045] According to a highly preferred embodiment, the aperture is integrally and / or monolithically formed with the valve body. In this case, the aperture can be formed directly when producing the valve, which is particularly efficient.

[0046] However, in another preferred embodiment, the aperture is a separate insert, which is fixed in the valve body. In this case, the aperture can be provided as a retrofit part, which can be mounted in the ball valve after production.

[0047] The aperture can be made from a material different than the valve body. For example, the aperture can be made from plastics material and the valve body from metal, e.g. steel or cast iron. This is in particular beneficial for relatively small ball valves.

[0048] According to another preferred embodiment, the aperture and the valve body are made from the same material, especially metal, e.g. steel. This is in particular the case if the aperture is integrally and / or monolithically formed with the valve body. Nevertheless, it may also be the case if the aperture is provided as a separate insert.

[0049] Preferably, apart from said aperture, the ball valve does not comprise any further aperture between the valve member and said aperture and / or downstream said aperture. Such configurations are ensure a compact design as well as good cavitation performance and flow noise reduction.

[0050] The ball valve preferably is configured as a flow control device allowing for continuously regulating a flow rate of a liquid.

[0051] In particular, the ball valve is configured such that the valve member can be rotated continuously between a fully closed positon, in which no liquid flows through the ball valve, and a fully open position, in which a maximum flow of liquid flows through the ball valve. In this case, the flow of the liquid depends on the rotational position of the valve member. Thereby, in the fully open position, a longitudinal axis of the aperture, especially of the through hole, of the valve member preferably is positioned essentially coaxial to a longitudinal axis of the fluid passage of the aperture.

[0052] In particular, the valve member is coupled to an actuator which is configured for rotating the valve member. The actuator can e.g. be selected from a manual actuator, e.g. a handle, and / or a motorized actuator, e.g. a servomotor. The actuator can for example be coupled to the valve member with an axis and / or a stem.

[0053] Another aspect of the invention is directed to a heating, ventilation, or air conditioning (HVAC) system comprising a ball valve as described above. The ball valve can for example be used to control the flow of cooling media and / or heating media, especially water, in the HVAC system.

[0054] However, the balls valve can be used for any other applications in which a flow of a liquid, such as e.g. water, needs to be controlled. Especially preferred, the ball valve can be used in process industry, e.g. for supplying and / or discharging process liquids.

[0055] A further aspect of the present invention is directed to an aperture for use in a ball valve as described above, whereby the aperture comprises a fluid passage with a hollow tapered section, which is configured such that a cross-sectional area of the fluid passage decreases from an initial cross-sectional area at an upstream end of the aperture in an intended direction of flow of the liquid to a minimum cross-sectional area of the fluid passage at the downstream end of the hollow tapered section.

[0056] As still further aspect of the invention is directed to the use of an aperture for reducing or avoiding cavitation and / or flow noise in a ball valve.

[0057] Thereby, in particular, the ball valve has a valve body with an inlet port and an outlet port, whereby a rotatable valve member in the form of a spherical body with an aperture, especially a through hole, is arranged in the valve body for controlling a flow of a liquid flowing from the inlet port along a flow path of the ball valve to the outlet, and whereby the aperture is arranged at a downstream side of the valve member in the flow path for generating a pressure drop in a liquid flowing along the flow path, whereby the aperture comprises a fluid passage with a hollow tapered section, which is configured such that a cross-sectional area of the flow path in the ball valve decreases from an initial cross- sectional area at an upstream end of the aperture in an intended direction of flow of the liquid to a minimum cross-sectional area of the flow path at the downstream end of the hollow tapered section and downstream the minimum cross-sectional area, the cross-sectional area of the flow path increases to an enlarged cross-sectional area, whereby the enlarged cross-sectional area downstream the aperture is larger than the initial cross-sectional area at the upstream end of the aperture. Other advantageous embodiments and combinations of features result from the detailed description below and the entirety of the claims.

[0058] Brief description of drawings

[0059] The drawings used to explain the embodiments show:

[0060] Fig. 1 A longitudinal section through a first exemplary ball valve with an aperture comprising a fluid passage with a hollow tapered section having a truncated circular cone shape form;

[0061] Fig. 2 A detailed view of the longitudinal section through the aperture of the ball valve of Fig. 1;

[0062] Fig. 3 A front view along the flow direction on the upstream side of the aperture shown in Fig. 2;

[0063] Fig. 4 A detailed view of the section marked with a dashed circle in Fig. 1 ;

[0064] Fig. 5 A longitudinal section through a second aperture comprising an expanding section downstream the hollow tapered section;

[0065] Fig. 6 A longitudinal section through a third aperture whereby the flow path decreases stepwise in two steps from the initial cross-sectional area at the upstream end to the minimum cross-sectional area at the downstream end.

[0066] In the figures, the same components are given the same reference symbols.

[0067] Exemplary embodiments

[0068] Fig. 1 shows a longitudinal section through an exemplary ball valve 1 comprising a valve body 10 with an inlet port 1 1 at an upstream side with respect to an intended flow direction and an outlet port 12 at a downstream side with respect to the intended flow direction. The flow path along the intended flow direction F in the ball valve has a circular cross-sectional area.

[0069] Within the valve body 10, a rotatable valve member 20 in the form of a spherical body with a cylindrical through hole 23 along the central axis is rotatably mounted. The through hole 23 has a constant circular cross-sectional area between the upstream side 21 and the downstream side 22. In Fig. 1, the valve member 20 is shown in the fully open position. By rotating the valve member 20 around the rotational axis R, a flow of liquid from the inlet port 1 1 along the flow path F of the ball valve 1 to the outlet port 12 can be controlled. If, with respect to the situation shown in Fig. 1, the valve member is rotated by 90° around the rotational axis R, the valve member can be brought in the fully closed position.

[0070] At the upper side, the valve member 20 comprises a grove 24 for receiving a stem (not shown in Fig. 1) that allows for coupling the valve member 20 with an actuator (not shown in Fig. 1), which is configured for rotating the valve member 20.

[0071] At a downstream side 22 of the valve member 20, there is an aperture 30 in the flow path F for generating a pressure drop in a liquid flowing along the flow path F. The aperture 30 comprises a fluid passage with a hollow tapered section 33 having a truncated circular cone shape form.

[0072] Thereby, a cross-sectional area of the flow path F decreases from an initial cross-sectional area 35 at an upstream end 31 of the aperture 30 in an intended direction of flow of the liquid to a minimum cross-sectional area 36 of the flow path F at the downstream end 32 of the hollow tapered section 33.

[0073] Downstream the minimum cross-sectional area 36, the cross-sectional area of the flow path F increases to an enlarged cross-sectional area 37, whereby the enlarged cross-sectional area 37 downstream the aperture 30 is larger than the initial cross-sectional area 35 at the upstream end 31 of the aperture 30. For example, the enlarged cross-sectional area 37 is about 1.5 times as large as the initial cross-sectional area 35.

[0074] A transition from the minimum cross-sectional area 36 to the enlarged cross-sectional area 37 is a single step-like transition.

[0075] Fig. 2 shows a detailed view of the longitudinal section through the aperture 30 of Fig. 1. In Fig. 2, the opening angle A of the truncated cone, which for example is 5°, is indicated. In this exemplary embodiment, over the whole length of the hollow tapered section 33, in every point of the boundary surface 34 defining the flow path F in the hollow tapered section 33, an angle of inclination of an imaginary tangent plane in said point, with respect to the intended flow direction or the flow path F, respectively, is 5°.

[0076] Furthermore, from Fig. 2, one can recognize the step-like transition at the downstream end 32 of the aperture 30.

[0077] Fig. 3 shows a front view along the flow path F onto the upstream side 31 of the aperture 30 of Fig. 1 and 2. As evident from Fig. 3 the flow path F in the aperture 30, as in the other sections of the ball valve, has a circular cross-sectional area.

[0078] Fig. 4 shows a detailed view of the section D marked with a dashed circle in Fig. 1 . As shown in Fig. 4, an edge radius R of an edge 34. 1 defining the minimum cross-sectional area 36 is at most 2% of the minimum diameter of the minimum cross-sectional area 36.

[0079] Fig. 5 shows a longitudinal section through a second aperture 30'. At the upstream end 31', the second aperture 30' is essentially identical to aperture 30 shown in Fig. 2. However, at the downstream end 32' of the hollow tapered section 33', which has the shape of a truncated circular cone, and downstream the minimum cross-sectional area 36', the second aperture 30' comprises an expanding section 38', which is configured such that a cross- sectional area of the flow path F continuously increases from the minimum cross-sectional area 36' to the enlarged cross-sectional area 37'.

[0080] The expanding section 38' has the shape of a truncated circular cone with an opening angle A2 ' of for example 80°. Thus, in the whole expanding section 38', in every point of a boundary surface 39' defining the flow path, an angle of inclination of an imaginary tangent plane in said point, with respect to a in intended flow direction F, is for example 80°.

[0081] A length L T of the tapered section 33' is larger than a length L2' of the expanding section 38', e.g. L T is equal to 6 times L2'.

[0082] Fig. 6 shows a longitudinal section through a third aperture 30". In this aperture, the hollow tapered section 33" is configured such that the cross-sectional area of the flow path decreases stepwise in two steps from the initial cross-sectional area 35" at the upstream end 31" to the minimum cross-sectional area 36" at the downstream end 32" of the third aperture 30".

[0083] The apertures 30, 30', 30" can be provided as separate parts, which can be mounted in the ball valve, e.g. as a retrofit part. However, it is possible as well to form the apertures 30, 30', 30" integrally with the valve body.

[0084] Tests with the ball valve 1 shown in Fig. 1 showed that cavitation and flow noise can be reduced essentially over the whole operational range of the valve, when compared to a ball valve without an aperture or when compared to a ball valve with an aperture not having hollow tapered sections. The cavitation factor z of the ball valve according to Fig. 1 was found to be > 0.45.

[0085] It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted.

[0086] Especially, the ball valve 1 can be configured such that the flow path at least section-wise has a non-circular cross-sectional area. Likewise, the fluid passages of the apertures 30, 30', 30" can have a non-circular cross-sectional area, at least in sections.

[0087] Instead of a continuously expanding section 38', the expanding section 38' may be configured such that it comprises at least one step-like transition.

[0088] In summary, it is to be noted that the invention provides highly beneficial ball valves, which are compact in size and advantageous with regard to cavitation and flow noise over the whole operational range of a valve. In particular, the inventive ball valves work for low as well as for high flow coefficients while having a high cavitation factor.

Claims

Claims1. Ball valve ( 1) having a valve body (10) with an inlet port ( 1 1) and an outlet port ( 12), whereby a rotatable valve member (20) in the form of a spherical body with an aperture, especially a through hole (23), is arranged in the valve body ( 10) for controlling a flow of a liquid from the inlet port ( 1 1) along a flow path (F) of the ball valve ( 1) to the outlet port ( 12), characterized in that at a downstream side (22) of the valve member (20), there is an aperture (30, 30', 30") in the flow path (F) for generating a pressure drop in a liquid flowing along the flow path (F), whereby: a) The aperture (30, 30', 30") comprises a fluid passage with a hollow tapered section (33, 33', 33"), which is configured such that a cross-sectional area of the flow path (F) decreases from an initial cross-sectional area (35, 35', 35") at an upstream end (31, 31', 31") of the aperture (30, 30', 30") in an intended direction of flow of the liquid to a minimum cross-sectional area (36, 36', 36") of the flow path (F) at the downstream end (32, 32', 32") of the hollow tapered section (33, 33', 33"); and b) downstream the minimum cross-sectional area (36, 36', 36"), the cross-sectional area of the flow path (F) increases to an enlarged cross-sectional area (37, 37', 37"), whereby the enlarged cross-sectional area (37, 37', 37") downstream the aperture (30, 30', 30") is larger than the initial cross-sectional area (35, 35', 35") at the upstream end (31, 31', 31") of the aperture (30, 30', 30").

2. Ball valve according to claim 1, whereby, in an intended flow direction, the cross- sectional area of the flow path (F) continuously decreases at least in a subsection of the hollow tapered section (33), preferably the cross-sectional area of the flow path (F) continuously decreases over the whole length of the hollow tapered section (33).

3. Ball valve according to claim 2, whereby, at least in the continuously decreasing subsection of the hollow tapered section (33), in particular over the whole length of the hollow tapered section (33), in every point of a boundary surface (34) defining the flow path (F) in the in the subsection or in the whole hollow tapered section (33), an angle of inclination of an imaginary tangent plane in said point, with respect to an intended flow direction, is at least 3°, especially 3 - 25°, in particular 4 - 10°, highly preferred 4 - 6°.

4. Ball valve according to any of preceding claims, whereby, in an intended flow direction, the cross-sectional area of the flow path (F), at least in a subsection of the hollow tapered section (33), especially over the whole length of the hollow tapered section (33), decreases stepwise in at least two or more steps.

5. Ball valve according to any of preceding claims, whereby a transition from the minimum cross-sectional area (36) to the enlarged cross-sectional area (37) is a single step-like transition.

6. Ball valve according to any of preceding claims, whereby downstream the minimum cross-sectional area (36'), the aperture (30') comprises an expanding section (38'), which, at least in a subsection, is configured such that a cross-sectional area of the flow path (F) continuously increases from the minimum cross-sectional area (36') to the enlarged cross-sectional area (37').

7. Ball valve according to claim 6, whereby in every point of a boundary surface defining the flow path (F) in the continuously increasing subsection of the expanding section (38'), an angle of inclination of an imaginary tangent plane in said point, with respect to a in intended flow direction, is at least 45°, especially at least 80°.

8. Ball valve according to any of claims 6 or 7, whereby, measured in an intended direction of flow, a length (L 1') of the tapered section (33') is larger than a length (L2') of the expanding section (38').

9. Ball valve according to any of preceding claims, whereby an edge radius (R) of an edge (34.1) of the aperture (30) defining the minimum cross-sectional area (36) is at most 4%, especially at most 2%, in particular at most 1%, of a maximum diameter of the minimum cross-sectional area (36).

10. Ball valve according to any of preceding claims, whereby the hollow tapered section (33) of the aperture (30) has a truncated cone shaped form, especially a truncated circular cone shape form, whereby an opening angle (A) of the truncated cone is at least 3°, especially 3 - 25°, in particular 4 - 10°, highly preferred 4 - 6°.

1. Ball valve according to any of preceding claims, whereby the ball valve is configured such that the flow path (F) is a straight line. . Ball valve according to any of preceding claims, whereby a cross-sectional area of the aperture, especially of the through hole, defining the flow path (F) in the rotatable valve member (20) is essentially identical to the initial cross-sectional area (35) of the aperture (30). . Ball valve according to any of preceding claims, whereby the aperture (30, 30', 30") is integrally and / or monolithically formed with the valve body ( 10). . Ball valve according to any of claims 1 - 12, whereby the aperture (30, 30', 30") is a separate insert, which is fixed in the valve body ( 10). . Ball valve according to any of preceding claims, whereby apart from said aperture (30, 30', 30"), the ball valve does not comprise any further aperture between the valve member (20) and said aperture (30, 30', 30") and / or downstream said aperture (30, 30', 30"). . Ball valve according to any of preceding claims, whereby the ball valve is configured as a flow control device allowing for continuously regulating a flow rate of a liquid. . Heating, ventilation, and / or air conditioning system comprising a ball valve according to any of preceding claims. . Aperture (30, 30', 30") for use in a ball valve ( 1) as described in any of preceding claims whereby the aperture (30, 30', 30") comprises a fluid passage with a hollow tapered section (33), which is configured such that a cross-sectional area of the fluid passage decreases from an initial cross-sectional area (35, 35', 35") at an upstream end (31, 31', 31") of the aperture (30, 30', 30") in an intended direction of flow of the liquid to a minimum cross-sectional area (36, 36', 36") of the fluid passage at the downstream end (32, 32', 32") of the hollow tapered section (33, 33', 33"). . Use of an aperture (30, 30’, 30") for reducing or avoiding cavitation and / or flow noise in a ball valve (1), the ball valve having a valve body ( 10) with an inlet port ( 1 1) and anoutlet port ( 12), whereby a rotatable valve member (20) in the form of a spherical body with an aperture, especially a through hole (23), is arranged in the valve body ( 10) for controlling a flow of a liquid flowing from the inlet port (1 1) along a flow path (F) of the ball valve ( 1) to the outlet port (12), and whereby the aperture (30, 30', 30") is arranged at a downstream side (22) of the valve member (20) in the flow path (F) for generating a pressure drop in a liquid flowing along the flow path (F), whereby the aperture (30, 30', 30") comprises a fluid passage with a hollow tapered section (33), which is configured such that a cross-sectional area of the flow path (F) in the ball valve decreases from an initial cross-sectional area (35) at an upstream end (31) of the aperture (30, 30', 30") in an intended direction of flow of the liquid to a minimum cross- sectional area (36) of the flow path (F) at the downstream end (32) of the hollow tapered section (33) and downstream the minimum cross-sectional area (36), the cross-sectional area of the flow path (F) increases to an enlarged cross-sectional area (37), whereby the enlarged cross- sectional area (37) downstream the aperture (30, 30', 30") is larger than the initial cross-sectional area (35) at the upstream end (31) of the aperture (30, 30', 30").

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