This invention relates to a valve assembly com¬ prising a housing provided with an inlet and an outlet for fluid and a spherical body rotatably arranged in the valve housing between the in- and outlet and mount¬ ed sealingly against said valve housing, said valve body being provided with fluid flow passages.

For adjusting a fluid flow conventional ball valves comprising two throttles in series with a fixed volume enclosed between said throttles have been found to be suitable. However, in high pressure conditions high flow rates are created at these throttles depend¬ ing on small cross-sections of an inconsiderable exten- sion in the direction of flow which may cause cavita- tion and a high sound level. The most critical movement in adjustment is when the first free cross-section, especially against the outlet side, opens. In this position the flow way made free should offer a great flow resistance also at small flowing amounts.

It is the object of the invention to provide a - simple and, at the same time, efficient device for ad¬ justing a fluid flow where disadvantages of cavitation and a high sound level are avoided. For this purpose a device having the characteris¬ tic features defined in the claims is suggested accord¬ ing to the invention.

The invention is described in greater detail in the form of non-limiting examples with reference to the enclosed drawings, wherein Fig . 1 shows a longitudinal section of a valve according to a first embodiment of the invention, Fig . 2 shows the valve body according to the section I I—I I in Fig. 1, Fig . 3 shows a longitudin¬ al section of the valve body with an opening angle (X = 25°, Fig . 4 shows a section corresponding to Fig. 3 but

with the opening angle (X = 45°, Fi . 5 shows also a section corresponding to Fig. 3 with the opening angle O = 56' Fig . 6 shows a section according to VI-VI in Fig. 7 of a second embodiment of the valve, and Fi . 7 shows the valve according to the section VII-VII in Fig. 6.

With reference to Fig. 1 the ball valve comprises a valve housing 1 provided with an inlet 2 and outlet 3 and a spherical valve body 4 rotatably arranged in the valve housing 1. The valve body 4 is sealingly mounted against an annular space 5 formed in the valve housing 1 by means of two valve seat rings 6. The valve seat rings 6 are fixedly connected to the valve housing 1 by their outer peripheries and have a clearance to the valve housing 1 at their inner peripheries in order to allow a resilient motion of the valve body 4.

The valve body 4 (Figs. 1, 2) is rotatable by means of a push rod (7) fixedly connected to the valve body 4 and is provided with two groups of passing flow passages 8, 9. The flow passages 8, 9 with circular cross-sections are preferably grooved in transversal direction, for example by threads. The groups of pas¬ sages 8, 9 are arranged on both sides of the diametri¬ cal plane, the passages 8 having a smaller diameter than the passages 9. The valve body 4 further comprises two smooth flow passages 10 of a larger diameter ar¬ ranged in said plane. When the valve is closed all the passages end in the space 5. On the other hand, at an open valve the passages end in the in- and outlet 2 , 3 , as is apparent from Fig. 1.

The mode of operation of the valve will be de¬ scribed in the following by the aid of Figs. 3-5, where Fig. 3 shows the valve body with the opening angle (X = 25°. In this case only a few number of passages 8 and 9, respectively, are opened. The substantial fluid flow way is marked by arrows. Thus, the fluid streams

through a first throttle position in the form of pas¬ sages 8 into the annular space 5 and around half the periphery in order to thereafter stream out through a second throttle in the form of passages 9. The passages 8 have a small diameter which causes a great flow re¬ sistance and consequently a great fall of pressure. The grooves of the passages cause a still more increased flow resistance and greater fall of pressure simultane¬ ously with a lower flow rate. The above also applies to the passages 9, which, however, have a somewhat larger diameter in order to reduce the flow rate and the fall of pressure, the risk of cavitation being reduced.

Fig. 4 shows the valve body 4 with the opening angle (X = 45°, all the passages 8 being opened and end- ing in the inlet 2 and the space 5 and all the passages 9 also being opened but ending in the space 5 and the outlet 3. This means that a full flow with a maximum fall of pressure can pass the valve.

When the valve is opened more than 45° (Fig. 5) a part of the fluid can stream directly from the inlet to the outlet, this share of fluid increasing by increas¬ ing valve opening. At the same time the passages 10 are opened for a direct fluid flow from the inlet 2 to the outlet 3 which reduces the fall of pressure across the valve.

Thus, when the valve is opened from 0° to 45° the flow will increase to its maximum maintaining a high fall of pressure. With continued opening of the valve the fall of pressure is successively reduced to get down to a minimum at an opening of 90° when a direct flow is reached in all the passages.

In Figs. 6-7 another embodiment of the invention is shown where the valve body 4 is turned out and pro¬ vided with a cylindrical insert 11. The insert 11 com- prises a number of concentric, spaced apart, tubular

members 12 with corrugated insert members 13 placed in the interspaces. In this way zigzagged flow passages 14 are formed which are in fluid connection with flow pas¬ sages 15 of a circular cross-section arranged in the valve body 4. The fluid connection is preferably formed so that each flow passage 15 can end in two separate passages 14.

The mode of operation of the valve agrees with what is described for the first embodiment but enables to reach a still higher fall of pressure without any risk of cavitation.

Of course modifications of the valve assembly are possible within the scope of the inventive idea. Thus, the number, size and location of the passages can for example be varied in different ways depending on which adjusting characteristic is desired. The passages can further be made conical with a cross-section increasing towards the outlet.