EP0222816A1

EP0222816A1 - Centrifugal separator

Info

Publication number: EP0222816A1
Application number: EP19860902946
Authority: EP
Inventors: Jan Setterberg
Original assignee: Alfa Laval Separation AB
Current assignee: Alfa Laval Separation AB
Priority date: 1985-04-30
Filing date: 1986-04-29
Publication date: 1987-05-27
Also published as: WO1986006300A1; SE8502101D0; JPS62502672A

Abstract

Un séparateur centrifuge comprend un rotor ayant à sa périphérie un dispositif de soupape. Le dispositif de soupape comprend un corps de soupape (9) radialement mobile agencé dans une position radialement intérieure de façon à résister à l'influence de la force centrifuge et à fermer un passage d'évacuation (8) d'un liquide contenu dans une chambre agencée à l'intérieur du rotor, et agencé dans une position radialement extérieure pour maintenir ouvert ledit passage. L'objectif de l'invention est de créer un séparateur centrifuge qui ne perd que de petites quantités de liquide et dans lequel le dispositif de soupape crée une faible résistance à l'écoulement du liquide qui sort par le passage d'évacuation (8). A cet effet, le dispositif de soupape est muni d'une première chambre de soupape (12), d'une deuxième chambre de soupape, d'un élément (14) qui pousse le corps de soupape (9) radialement vers l'intérieur en cas de surpression dans le première chambre de souape (12), d'un élément mobile (11) qui forme une paroi mobile entre lesdites chambres de soupape (12, 13) et est exposé aux pressions qui règnent dans celles-ci, d'un permier canal et d'un deuxième canal séparé (18) qui fournissent le liquide de commande aux chambres respectives et d'un orifice d'évacuation (20) formé à la périphérie du rotor pour décharger le liquide de commande contenu dans le deuxième canal (19), cet orifice d'évacuation (20) ayant un débit limité.A centrifugal separator includes a rotor having at its periphery a valve device. The valve device comprises a radially movable valve body (9) arranged in a radially inner position so as to resist the influence of centrifugal force and to close a discharge passage (8) of a liquid contained in a chamber arranged inside the rotor, and arranged in a radially external position to keep said passage open. The object of the invention is to create a centrifugal separator which loses only small quantities of liquid and in which the valve device creates a low resistance to the flow of liquid which leaves through the evacuation passage (8). . To this end, the valve device is provided with a first valve chamber (12), a second valve chamber, an element (14) which pushes the valve body (9) radially inwards. in the event of overpressure in the first valve chamber (12), a movable element (11) which forms a movable wall between said valve chambers (12, 13) and is exposed to the pressures prevailing therein, d '' a first channel and a second separate channel (18) which supply the control liquid to the respective chambers and a discharge orifice (20) formed at the periphery of the rotor for discharging the control liquid contained in the second channel (19), this discharge orifice (20) having a limited flow.

Description

Centrifugal separator

The present invention concerns a centrifugal separator with a rotor, having a valve device located at its periphery. The valve device comprises a radially movable valve body arranged in a radial inner position and against the influence of the centri¬ fugal force to close an outlet passage for a liquid contained in a chamber within the rotor and in a radial outer position to keep said outlet passage open.

In a previously known centrifugal separator of this kind a liquid mixture is intended to be centrifugally treated in a separation chamber within the rotor, a specific heavier compo¬ nent of the liquid mixture being separated and accumulated at the periphery of the separation chamber. The component accumulated in. this way is thrown out of the separation chamber through an outlet which is openable during operation. The outlet can be opened by axially moving by means of the pressure from the mixture of liquids contained in the separation chamber, a slide valve, which together with a rotor part defines the separation chamber, said pressure acting axially on the slide valve against the pressure action of a closing liquid which is contained in a closing chamber formed by the slide valve and the rotor wall. If the axial force acting on the slide valve by the pressure from the closing liquid is larger than the axial force by the pressure of the liquid mixture, the slide valve moves in a closing direction and is pressed into sealing abutment against a sealing surface.

The opening and closing procedure can be controlled by letting closing liquid out of the closing chamber through a peri¬ pheral outlet passage provided with a contol valve. The control valve in turn can be controlled by means of a control liquid, which by its pressure acts radially inwards on a radially movable valve body against the influence of the centrifugal force. The pressure of the control liquid acts on the valve body in a direction closing the outlet passage for the closing liquid, whereas the centrifugal force thus is acting on the valve body in an opening direction.

During this opening and closing procedure closing liquid and control liquid are supplied centrally through supply channels in the rotor. The supply channels for the control liquid has a peripherally located throttled outlet, out of which control liquid flows during most of the time of operation, while the control valve is kept closed by the pressure of the control liquid in the control channels. The control valve can be opened by cutting off the supply of control liquid, whereby the pres¬ sure acting on the valve body successively decreases and, finally, the valve body moves radially outwards as a consequence of the centrifugal force and opens the outlet passage for the closing liquid. By arranging a control valve for letting out of closing liquid in this mannef it is possible to design the outlet passage for the closing liquid such that it opens in a surface in the rotor, which is facing radially outwards, and to design a valve body radially movable to and from this surface. Thereby, a throughflow area of the flow path through the control valve can be accomplished, which increases rapidly when the valve body moves in its opening direction, which is desirable for a rapid outflow of closing liquid from the closing chamber.

However, the known valve arrangement means that large amounts of control liquid get lost because of the fact that such control liquid during most of the time of operation is forced out of the centrifuge rotor through the throttled outlet at a high pressure. With the control liquid even its content of energy is lost.

The main object of the present invention is to provide a ceαtri- fugal separator of the Initially described kind, wherein a liquid contained in the rotor can be let out through a valve device giving a low flow resistance and being designed such that no control liquid has to be lost only for retainment of the valve device in a position in which said outlet passage is closed.

This object can be achieved according to the invention by providing a centrifugal separator of this kind with a valve device, which in addition to said valve body comprises two valve chambers, a first and a second valve chamber, means arranged to press the valve body radially inwards at an overpressure in the first valve chamber, a radially movable member, which forms a movable wall between said valve chambers and is exposed to pressures prevailing therein, a first and a separate second channel, for the supply of control liquids to the first and second valve chambers, respectively, which channels extend between the valve chambers and central parts of the rotor, and an outlet at the periphery of the rotor for draining of control liquid out of said second channel. This outlet has such a limited through flow capacity that upon supply of a predeter¬ mined minimum flow of control liquid to the second channel a certain overpressure is obtained in the second chamber, the movable member being arranged to be moved radially inwards by said overpressure in the second valve chamber, so that liquid is displaced out of the first valve chamber and further through the first channel towards the centre of the rotor.

In a preferred embodiment of the invention said outlet passage opens in a surface in the rotor, which is facing essentially ra- dially outwards, the valve body being movable radially to and from sealing abutment against said surface. Hereby a through- flow area of the openable flow path through the control valve is obtained, which increases quickly when the valve body moves in its opening direction. In another embodiment of the invention the first valve chamber of the valve device is located radially outside of the movable member, and the second valve chamber of the valve device is located radially inside of the same. The movable member is arranged to move radially inwards at an overpressure in the first valve chamber - against the influence of the centrifugal force and the pressure in the second valve chamber - and via an element, radially movable through and sealing against the wall of the second valve chamber to press the valve body mechanically toward closing of the outlet passage. Upon supply of the second control liquid to the second valve chamber the pressure therein will increase to such a degree that it overcomes the radial force on the movable member resulting from the pressure in the first valve chamber, whereby the valve body by the centrifugal force is brought to move radially outwards and to open the outlet passage.

According to a further embodiment of the invention the first valve chamber of the valve device is located radially inside of the movable member and the second valve chamber is located radially outside of the same. In this embodiment the movable member is arranged to be pressed by centrifugal forces and the pressure in the first valve chamber radially outwards against the action of the pressure in the second valve chamber. A part of the valve body in this embodiment forms a radially inner wall, of the first valve chamber, which simultaneously operates as a pressure transmittning element for pressing the valve body radially inwards to sealing abutment against the rotor body at an overpressure in the first valve chamber. In addition to the outlet of the second channel in this embodiment even the inlet for the control liquid to the first valve chamber has been given a limited throughflow capacity by throttling means in the first channel. Before opening of the outlet passage in this centrifugal separator control liquid is supplied to the second valve chamber centrally via the second channel. The supply of control liquid then exceeds a predetermined minimum flow, which is deter- mined by the through flow capacity of the outlet of the second channel. The pressure in the second valve chamber hereby increases so much that it can move the movable member radially inwards, against the action of the centrifugal force and the pressure in the first valve chamber, and thereby displace the control liquid out of the first valve chamber and further through the first channel towards the centre of the rotor. After that the supply of control liquid to the second channel is cut off, whereby this channel and the second valve chamber are emptied of their contents out to the radius, at which the throttled outlet is located. The pressure in the second chamber then decreases and the movable member is thrown out. Because of the fact that the supply of control liquid to the first valve chamber is throttled, this means that the pressure in this valve chamber decreases, which influences the valve body. Hereby the valve body will be thrown radially outwards and will open the outlet passage. In the meantime control liquid is supplied to the first valve chamber through the throttled inlet and the pressure in this increases again. When the pressure has reached a certain level It is able to move the valve body radially inwards into sealing abutment against the opening of the outlet passage.

In order to ensure that the pressure in the second valve chamber is able to move the movable member radially inwards in the beginning of the opening procedure, the movable member may be provided with a larger effective pressure area facing radially outwards to the second valve chamber than its effective pressure area which facing radially inwards to the first valve chamber. In the hitherto proposed embodiments the liquid contained in said chamber can be constituted by any liquid present in the rotor, such as a liquid component separated in the separation chamber or the so called closing liquid in the closing chamber.

According to still another embodiment, which is specially adapted for centrifugal separators having a so called closing chamber, the very closing liquid is intended to operate also as a control liquid. The closing chamber in this case will function as a first channel for the supply of control liquid to the first valve chamber. This is possible according to the invention by providing the valve body with a throttled channel, which extends radially through the valve body and connects the first valve chamber with said outlet passage, so that, when the valve body is in a closing position, the firs^'t channel, i.e. the closing chamber, communicates with the first valve chamber via the outlet passage. By designing a centrifugal separator in this way the number of drilled channels in the rotor body and thus the manufacturing costs can be reduced. Even in this embodiment the moving member preferably may be provided with a larger effective pressure area facing radially outwards in the second valve chamber than its effective pressure surface facing radially inwards to the first valve chamber.

In the following the invention will be described more in detail with reference to the accompanying drawings, in which

figure 1 shows an axial section through a part of a centrifugal separator according to an embodiment of the invention,

figre 2 shows an axial section through a part of a centrifugal separator according to another embodiment of the invention,

figure 3 shows an axial section through a part of a centrifugal separator according to a preferred modification of the embodiment of the invention shown in figure 2, and

figure 4 shows an axial section through a part of a centrifugal separator according a further embodiment of the invention.

Corresponding details in the different figures have been alotted the same reference numbers.

_⁾ In figure 1 there is shown a part of a centrifugal separator which has a rotor body, which consists of a lower rotor part 1 and an upper rotor part 2, which in a not shown manner are connected to each other, for instance by means of a locking joint. Inside the lower rotor part 1 an axially movable slide valve 3 is arranged, which together with the upper rotor part 2 'forms a separation chamber 4. The slide valve 3 and the lower rotor part 1 define between themselves a closing chamber 5. The slide valve 3 is pressed by the pressure from a closing liquid being inside the closing chamber 5 to sealing abutment against the upper rotor part 2 against the action of the pressure from a mixture of liquids being inside the separation chamber 4, and thereby shutting off a connection between the separation chamber 4 and an outlet 6 for a specific heavier liquid component, which during separation has been thrown radially outwards and accumulated at the periphery of the separation chamber 4.

The closing chamber 5 is connected to the outlet chamber 7 via an outlet passage 8, which extends essentially radially outwards from the closing chamber 5 and is able to be opened and closed by means of a valve device. This valve device comprises a radially movable valve body 9 arranged in the outlet chamber 7 which valve body 9, when the outlet passage is closed, is pressed to sealing abutment against an essentially radially outwards facing surface, to which the outlet passage 8 opens. The outlet chamber 7 is connected to the surroundings of the rotor via an outlet channel 10. Radially outside the outlet chamber 7 there is formed a valve cavity in the lower rotor part 1. In this valve cavity there is arranged a radially movable member 11, which divides the valve cavity into a radially outer first valve chamber 12 and a radially inner second valve chamber 13. Between the movable member 11 and the valve body 9 a mechanically force transmitting element 14 is arranged radially movable through and sealed against a sleeve 15 in the separating wall 16 between the outlet chamber 7 and the second valve chamber 13. The first valve chamber 12 is separated from the surroundings of the rotor by means of a plug 17 and connected to a first channel 18 for the supply of control liquid from a centrally located supplying means (not shown) to this valve chamber 12. The second valve chamber 13 is connected to a second channel 19 for the supply of control liquid from a centrally located supplying means (not shown) to this second valve chamber 13. This second channel 19- is connected.to the surroundings of the rotor via an outlet 20, which has a limited through flow capacity.

The centrifugal separator shown in figure 1 operates in the following manner:

Upon start of the centrifugal separator control liquid is supplied centrally to the first channel 18 and the first valve chamber 12, which consequently are filled. The pressure from the control liquid in the first valve chamber 12 acting on a substantially larger effective pressure area than the pressure area of the valve body 9, on which the closing liquid in the closing chamber acts, at this increases to and is kept at such a pressure level that it is able to move the movable member 11, the force transmitting element 14 and the valve body 9 against the influence of the centrifugal force radially inwards and press the valve body to sealing abutment against an essentially radially outwards facing surface around the opening of the outlet passage 8. During this phase the second valve chamber 13 and the second channel 19 are emptied of its content of control liquid. As soon as the opening of the outlet passage 8 is closed the closing liquid can be supplied centrally to the closing chamber 5. The pressure acting on the slide valve 3 from the closing liquid at this time will be increasing and pressing the slide valve 3 to sealing abutment against the upper rotor part 2. When the connection between the separation chamber 4 and the peripheral outlet 6 is closed, the mixture of liquid, which is to be centrifugally treated, Is supplied to the separation chamber through a not shown central inlet. During the starting procedure the rotational speed of the rotor increases and reaches after a while the operational speed, at which the components in the mixture of liquids is separated in the separation chamber 4. The specific heavier component is thrown radially outwards during the separation and accumulates at the periphery of the separation chamber 4, while one or more specific lighter components are guided radially inwards toward one or more central outlets (not shown).

The opening of the connection between the separation chamber

4 and the peripheral outlets 6 is activated when a predetermined amount of specific heavier components has been accumulated at the periphery of the separation chamber, or at predetermined time intervals, and is carried out by supplying control liquid to the second channel 19 and the second valve chamber 13 from a centrally located supplying means. Hereby the pressure from the control liquid in the second valve chamber 13 increases, which pressure together with the pressure acting on the valve body 9 from the closing liquid in the closing chamber 5 via the force transmittning element 14 acts in radial direction outwards on the movable member 11 against the influence of the pressure from the control liquid contained in the first valve chamber 12 and the first channel 18. The total force, acting radially outwards on the movable member 11, increases thereby in such a degree that it is capable to move the movable member 11 and the valve body 9 radially outwards and to force the control liquid out of the first valve chamber 12 and further through the first channel 18 towards the centre of the rotor and to open the outlet passage 8 for the letting out of the closing liquid 5 contained in the closing chamber 5 Inside the radial level, at which the outlet passage 8 is connected to the closing chamber 5. The axial force acting on the slide valve 3 from the closing s) liquid remaining in the closing chamber 5 Is thereby decreasing and becomes smaller than the axial force from the mixture of 10 liquids contained in the separating chamber 4 on the same, whereby the connection between the separating chamber 4 and the outlet 6 is opened.

As soon as the supply of control liquid to the second channel 15 19 and the second valve chamber 13 is cut off, they will be drained of their liquid content through the outlet 20, whereby the pressure in the second valve chamber 13 and consequently the radial force acting on the movable member 11 decreases. The pressure of the control liquid in the first valve chamber 12 20 and the first channel 18 will hereby be able to press the movable member 11 and the valve body 9 radially Inwards and to cut off the outlet passage 8.

In this embodiment It is possible to control the time, during 25 which the passage between the separating chamber 4 and the outlet 6 is open. This can be done by controlling the time, during which liquid is supplied to the second channel 19 and the closing chamber 5. It also can be done by controlling the supply flow for one or both of these liquids. Preferably the 30 control Is done by controlling the time, during which the control liquid is supplied to the second channel 19 and the second valve chamber 13 with a relatively heavy flow. In this case the supply of closing liquid to the closing chamber 5 then can be done either continuously or intermittently. How much of 35 the liquid content in the separation chamber, which can be let out through the outlets 6, is determined by the radius at which the outlet passage 8 is connected to the closong chamber 5, i.e. the remaining amount of closing liquid in the radial outer portion of the closing chamber 5 acting in the closing direction on the slide valve 3. When the axial force of the pressure from the remaining closing liquid exceeds the axial force of the pressure from the remaining mixture of liquids in the separation chamber 4, the slide valve 3 moves in the closing direction and closes the connection.

Figure 2 shows an embodiment, in which the first valve chamber 12 is located radially inside the movable member 11 and the second valve chamber 13 is located radially outside the movable member 11. In this embodiment the first channel 18 has been provided with a throttling means 21 at the inl-et of the first valve chamber 12. Further, the first valve chamber 12 is de¬ fined radially inwards by a separating wall, which at the same time functions as a pressure transmitting element 14 in order to press the valve body radially inwards at an overpressure in the first valve chamber 12. The element 14 constitutes an integrated part of the valve body 9. As for the rest this embodiment corresponds to the one shown in figure 1.

The embodiment shown in figure 2 functions in a way that differs somewhat from the way described above with reference to figure 1. In the embodiment according to figure 2 the opening of the outlet 6 is activated by supplying control liquid to the second channel 19 and the second valve chamber 13. The pressure in the second valve chamber 13 will at this time be increasing enough to move the movable member 11 radially inwards and thereby to displace at least a part of the control liquid contained in the first valve chamber 13out of the same through the throttled inlet 21 and further through the first channel 18 towards the centre of the rotor. During this phase the valve body 9 remains in a position closing the outlet passage 8. Afterwards, when the supply of control liquid to the second channel 19 is cut off, this and the second valve chamber 13 are drained through the throttled outlet 20, whereby the movable member 11 is thrown radially outwards. The throttling means 21 in the inlet to the first valve chamber 12 is in this given a through flow capacity which is so much lower than the throttle device at the outlet 20 that the pressure in the first valve chamber decreases and becomes lower than the pressure necessary to keep the valve body 9 in a position closing the outlet passage 8. This results in that the valve body 9 moves radially outwards and opens the outlet passage 8 for letting the closing liquid out of the chamber 5. The outlet passage 8 remains open during the time that is necessary for the amount of control liquid having earlier been forced out of the first valve chamber 12 and further through the channel 18 towards the centre of the rotor, to reflow into the first valve chamber 12 through the throttled inlet 21. As soon as so much of the closing liquid has been let • out through the outlet passage 8 that the pressure from the same acting in closing direction on the slide valve 3 is lower than the pressure from the mixture of liquids contained in the separation chamber on the slide valve 3, the connection will be opened between the separation chamber 4 and the outlet 6. This connection will be kept open and will be shut off again according to the same procedure as the one already described in connection to the embodiment according to figure 1. As in the embodiment according to figure 1 the supply of the closing liquid to the closing chamber 5 in this one will be done either continuously or intermittently.

Figure 3 shows a preferred modification of the embodiment of the invention shown in figure 2. The preferred embodiment differs from the above described embodiment by designing the radially movable member 11 with a radial outer portion 11a and a radial inner portion lib. The outer portion 11a has been given a larger effective pressure area facing radially outwards to the second valve chamber 13 than the effective pressure area of the inner portion lib facing radially inwards to the first valve chamber 12. In order to make this possible the barrel, in which the movable member 11 moves, has been divided in two, i.e. one barrel to each part of the movable member 11, and the barrel for the outer portion 11a has been provided with a communication with a surrounding atmosphere around the rotor in the form of an evaporation channel 22 at its radially innermost part, which is separated from communication with the second valve chamber 13 by the outer portion 11a. Hereby it is secured that the pressure in the second valve chamber is capable to move the movable member 11 inwards during the introductory phase of the opening procedure.

In both the embodiment according to figure 2 and the embodiment according to figure 3 it is possible to have the valve body 9 to move rapidly radially outwards when the supply of control liquid to the second channel 19 is cut off. This means that a wanted amount of the closing liquid rapidly can be let out of the closing chamber 5 by means of a small number of valve devices. The rapid letting out of closing liquid is of great importance to make it possible even for a predetermined amount of separated specific heavier component accumulated at the periphery of the separating chamber 4 to be let out rapidly, which is desirable at many applications.

In the embodiments according to figures 2 and 3 it is possible to control the time, during which the connection between the separation chamber 4 and the outlet 6 is open and the amount of liquid let out through the connection by controlling the time, during which liquid is supplied to the second channel 19. Indirectly the amount of liquid, which Is displaced out of the first valve chamber 12 through the throttled inlet and further through the first channel 18 towards the centre of the rotor hereby is controlled.

The so far described and in the figures 1, 2 and 3 shown embodiments of a centrifugal separator according to the inven- tion altogether have been provided with an axially movable slide valve 3, which is arranged to open and close the connection between the separation chamber 4 and one or more outlets 6. In the closing direction the slide valve is influenced by a closing liquid contained in a closing chamber 5. The liquid which flows out of the outlet passage 8 consists in these cases of said closing liquid. However, it is possible to design a centrifugal separator according to the invention without any such slide valve 3, namely such that the liquid flowing out of the outlet passage 8 consists of a liquid separated in the separation chamber 4, In which the valsre device preferably being located nearby the outermost periphery of the separation chamber 4.

In figure 4 an embodiment of the invention is shown which especially has been adapted for centrifugal separators having such a slide valve 3 and in which the liquid flowing out through the outlet passage 8 consists of closing liquid. In this embodiment the closing liquid also functions as a control liquid, the closing chamber 5 functioning as a first channel for the supply of control liquid to the first valve•chamber 12. This is made possible by the fact that the throttled inlet to the first valve chamber 12 consists of a channel 23, which extends essentially radially through the valve body 9, in a way that, when the valve body 9 is in a position closing the outlet passage 8, the closing chamber 5 communicates with the first valve chamber 12 via the outlet passage 8 and the channel 23. As for the rest this embodiment corresponds to the embodiment shown in figure 3.

Upon start of the centrifugal separator shown in figure 4 control liquid supplied to the second channel 19 and the second valve chamber 13 with a flow, which exceeds the through- flow capacity of the throttled outlet 20. Hereby, the pressure in the second valve chamber 13 increases and presses the radial movable chamber 11 radially inwards towards the valve body 9 against the influence by the centrifugal force, the valve body 9 being pressed radially inwards into sealing abutment against an annular part of a sealing surface facing essentially radially outwards around the opening of the outlet passage 8. After that it is possible to supply closing liquid to the closing chamber, whereby the separation chamber 4 is closed and the mixture of liquids, which is to be centrifugally treated, can be supplied to the separation chamber 4. A portion of the supplied closing liquid passes through the throttled channel 23 into the first valve chamber 12 and fills it up. Because of the fact that the cross section area in the first valve chamber.12 is larger than the cross section area of the outlet passage 8, the valve bo'dy 9 is kept in a position closing the outlet passage 8 even -if there is no overpressure in the second valve chamber 13. Without opening of the outlet passage 8 a supply of control liquid to the second channel 19 hereby can be diminished to a flow, which is somewhat less than the throughflow capacity of the throttled outlet 20, in a way such that the movable member slowly is moving radially outwards. The speed of the movable member 11 has to be so low that the flow through the throttled channel 23 to the first valve chamber 12 can fill up the increasing of volume, which the first valve chamber 12 hereby undertakes.' As soon as the movable member 11 has reached its radially outermost end position, the supply of control liquid to the second channel 19 can be cut off completely.

In the same way as in the above embodiments the proceedings for the letting out of specific heavyer component accumulated at the periphery of the separation chamber in this one is started with the supply of control liquid to the second valve chamber via the second channel 19. Hereby, the pressure from the control liquid in the second valve chamber 13 increases and moves the movab member 11 radially inwards. This member forces the control liquid out of the first valve chamber 12 through the throttled channel 23 and the outlet passage 8 and further towards the centre of the rotor in the closing chamber 5. When the supply of control liquid to the second channel 19 is cut off, the pressure in the second valve chamber 13 decreases rapidly and the movable member 11 and the valve body 9 are thrown by the centrifugal force radially outwards, and the outlet passage- 8 is opened and closing liquid is thrown out of the closing chamber 5 through the outlet passage 8 and further out through the outlet channel 10. Hereby, the pressure in the closing chamber 5 decreases and the slide valve moves downwards in the figure, whereby the connection between the separation chamber 4 and the outlet 6 opens. In this embodiment the outlet passage 8 is dosed by supplying control liquid again to the second chamber 19, whereby the. valve body 9 closes the outlet passage 8 in the same way as described in connection with start of this centrifugal separator.

If the mixture of liquids supplied to the separation chamber con¬ tains relatively large amounts of the specific heavier component, it is possible to omit to reduce the supply of control liquid to the second channel 19 before it is time again to open the outlet passage 8. Thereby, the movable member 11 is kept in its radial inner position until the supply of control liquid to the second channel 19 is cut off for the opening of the outlet passage 8.

In all embodiments shown in the figures the outlet passage 8 is connected to the closing chamber 5 at a radius which is smaller than the greatest radius of the closing chamber 5.

This means that the closing chamber only partly will be emptied, and consequently it is not either possible for the separation chamber 4 to be completely emptied. Naturally, it is quite possible to connect the outlet passage 8 at the largest radius of the closing chamber, so that the separation chamber 4 can be emptied completely.

Claims

1. Centrifugal separator with a rotor having a valve device located at its periphery, the valve device comprising a radially movable valve body (9) arranged in a radially inner position and against the influence of the centrifugal force to close an outlet passage (8) for a liquid contained in a chamber within the rotor, and in a radially outer position to keep said outlet passage (8) open, c h a r a c t e r i z e d i n that said valve device also comprises

- two valve chambers, a first valve chamber (12) and a second valve chamber (13),

- an element (14) arranged to press the valve body (9) radially inwards at an overpressure in the first valve chamber (12),

- a radially movable member (11), which forms a movable wall between said valve chambers (12, 13) and Is exposed to pressures prevailing therein,

- a first channel (18) and a separate second channel (19) for the supply of control liquids to the first and second chambers (12, 13) respectively, which channels extend between the valve chambers and central parts of the rotor, and

- an outlet (20) at the periphery of the rotor for draining of control liquid from said second channel (19), which outlet (20) has such a limited throughflow capacity that upon supply of a predetermined minimum flow of control liquid to the second channel (19) a certain overpressure is obtained in the second chamber (13), the movable member (11) being arranged to be moved radially inwards at said overpressure in the second valve chamber (13) so that liquid is displaced out of the first valve chamber (12) and further through the first channel (18) towards the centre of the rotor.

2. Centrifugal separator according to claim 1, c h a r a c ¬ t e r i z e d I n that said outlet passage (8) opens In a surface of the rotor, which is facing essentially radially outwards, the valve body (9) being movable radially towards and away from this surface.

3. Centrifugal separator according to claim 1 or 2, c h a ¬ r a c t e r i z e d i n that a throttle device (21) is arran¬ ged between said first channel (18) and the first chamber (12).

4. Centrifugal separator according to claim 3, c h a r a c ¬ t e r i z e d i n that the first chamber (12) is defined radially inwards by said element (14) and radially outwards by the movable member (11), said element (14)- being an integral part of the valve body (9).

5. Centrifugal separator according to claim 3 or 4, c h a ¬ r a c t e r i z e d i n that the movable member (11) is provided with a larger effective pressure area facing the second chamber (13) than the one facing the first chamber (12).

6. Centrifugal separator according to any of the claims 3-5, c h a r a c t e r i z e d i n that the movable member (11) is arranged to move radially inwards upon supply of control liquid to the second channel (19) during operation, as a result of the increasing pressure in the second valve chamber (13), and to move radially outwards as a result of the centrifugal force upon interruption of said supply, so that the pressure In the first chamber (12) decreases, whereby the valve body (9) moves radially outwards to open the outlet passage (8).

7. Centrifugal separator according to any of the claims 3-6, which is provided with a separation chamber (4) and a slide valve (3) arranged under influence from the pressure of a closing liquid contained in a closing chamber (5), formed by the slide valve (3) and a wall (1) of the rotor, to close and open outlets (6) for a component separated in the separation chamber, c h a r a c t e r i z e d i n that said chamber in the rotor is constituted by this closing chamber (5).

8. Centrifugal separator according to claim 7, c h a r a c ¬ t e r i z e d i n that the closing chamber (5) constitutes at least a part of the first channel (18), via which the first valve chamber (12) communicates with a central part of the rotor, the first channel (18) having communication with the first valve chamber (12) via the outlet passage (8) and a throttled channel (23) radially through the valve body (9)', when the valve body (9) is in a position closing the passage.

9. Centrifugal separator according to claim 1 or 2, c h a - r a c t e r i z e d i n that the movable member (11) is arranged to be moved radially inwards by an overpressure in the first chamber (12) and, thereby, via an element (14) to move the valve body (9) in the closing direction, and to be moved radially outwards by a predetermined pressure in the second chamber for movement of the valve body (9) in the opening direction.

10. Centrifugal separator according to claim 9, c h a r a c ¬ t e r i z e d i n that the movable member (11) is provided with a larger effective pressure area facing the second chamber (13) than the one facing the first chamber (12).