US3773253A - Centrifugal basket bottom valve machanism - Google Patents

Abstract

A cyclical basket having openings in its bottom structure for the removal of centrifuged solids is provided with bottom valve means which are opened and closed by positioning means driven by slow rotation of the basket. The valve means comprise leaves hinged to the spokes of the basket for downward swinging movement to a hanging, open position, with the hinges so disposed that during high speed rotation of the basket the leaves are urged toward closed position both by the pressure of ambient air and by centrifugal force. The positioning means rotate with and are displaceable in a limited path relative to the basket bottom; for example, a spider turnable on the basket hub is connected with the leaves through rigid links and universal joints. Suitable actuating means, for example, a non-rotary slip clutch member engageable axially with a mating rotary clutch member on the spider, cause the leaves to be closed by rotation of the basket in the centrifuging direction and to be swung open by rotation of the basket in the reverse direction. The links can form toggle joints locking the leaves closed against pressure applied to their upper side.

Description

Umted States Patent 11 1 1111 3,773,253

Laven Nov. 20, 1973 CENTRIFUGAL BASKET BOTTOM VALVE [57] ABSTRACT MACHANISM A cyclical basket having openings in its bottom struc- [75] Inventor: Thomas R. Laven, Hamilton, Ohio ture for the removal of centrifuged solids is provided [73] Assignee: The Western States Machine with q i i valve means.which are opened closed 66615355, Hamilton; by pos1t1on1ng means driven by slow rotation of the basket. The valve means compnse leaves hmged to the [22] Filed: May 25, 1972 spokes of the basket for downward swinging movement to a hanging, open position, with the hinges so [21] Appl' 256762 disposed that during high speed rotation of the basket the leaves are urged toward closed position both by [52] US. Cl. 233/20 R, 233/46 the pressure of ambient air and by centrifugal force. [51] Int. Cl B04b 11/00 The positioning means rotate with and are displace- [58] Field of Search 233/20 R, 20 A, 46, able in a limited path relative to the basket bottom; 233/47 R, 21, 22, 19 R, 19 A for example, a spider turnable on the basket hub is connected with the leaves through rigid links and uni- [56] References Cited versal joints. Suitable actuating means, for example, a UNITED STA PATENTS non-rotary slip clutch member engageable axially with 1,974,679 9/1934 Lindbergum 233/20 R a mating rotary clutch member on the spider, cause 1,101,549 6/1914 Hoffman 233/20 R the leaves to be closed by rotation of the basket in the 921,371 5 1909 Dibble 233 20 R centrifuging direction and to be swung p y rota- 3,294,317 12/1966 Moretti 233 20 R tion f th asket in th reverse ir t n- The links Primary Examiner-George H. Krizmanich Attorney-Albert C. Johnston SEQUENCE can form toggle joints locking the leaves closed against pressure applied to their upper side.

11 Claims, 6 Drawing Figures CONTROL PATENTEU NOV 2 0 I973 SHTT 1C? 2 l0 SEQUENCE CONTROL CENTRIFUGAL BASKET BOTTOM VALVE MACHANISM This invention relates to a bottom valve mechanism for a centrifugal basket of the kind used in cyclical centrifugal machines, as in sugar and chemical industries, for separating liquids from solids and retaining the solids until, after each centrifuging period,they are discharged from the side wall of the basket and removed by being passed downward through openings in the basket bottom structure.

The bottom structure of a centrifugal basket of that kind typically includes a circular bottom ring fixed about the inner edge of an annular bottom wall, a central hub secured to a spindle carrying the basket, spokes between the hub and the bottom ring, and openings between the spokes for the delivery of treated solids from the basket.

A basket bottom valve is usually provided for closing the bottom openings during periods of loading the basket and centrifuging its contents, together with means for displacing the valve after each centrifuging period so that the treated solids may be discharged through the bottom openings.

According to U. S. Pat. Nos. 2,667,974 and 2,694,494, the treated solids are discharged by a mechanical discharger brought into action upon rotation of the basket to and at a low speed in the direction opposite to that of the centrifuging rotation, and the bottom valve is a frusto-conical member which surrounds the basket shaft and is lifted and tilted away from the zone of action of the discharger during each discharging period.

U.S. Pat. No. 3,056,505 proposes a bottom valve having the form of a collapsible conical diaphragm connected with a sleeve slidable axially on the basket spindle by linkages which contract the diaphragm radially inwardly when the sleeve is raised and expand the diaphragm so that it will close the bottom openings when the sleeve is lowered.

US. Pat. No. 3,294,317 proposes a bottom valve constituted by a series of doors, or leaves, hinged to the hub of the basket bottom structure and connected through links to a rotary two-way air cylinder mounted slidably on a downward extension of the spindle hub. The leaves normally are held in an upward position in which they close the bottom openings, by compressed air admitted to the lower side of a piston in the rotary air cylinder. When the air pressure is shifted to the upper side of the piston, the cylinder and the links are forced downward so as to pull the leaves downward and radially inward from the basket bottom openings, thus enabling discharge of the centrifuged products.

The present invention provides a bottom valve mechanism having new features of construction and operation which enable a variety of practical advantages not previously attained in the art.

According to the invention, the basket bottom valv mechanism comprises valve means for the basket bottom openings which are displaced to and held in open or closed position as and when desired, typically being opened for the discharging operation of each centrifugal cycle and closed for and during the loading and centrifuging periods of the cycle, by positioning means which are displaceable in a limited path relative to the basket by power transmitted from rotation of the centrifugal basket itself.

Further according to the invention, displacement of the positioning means to move the valve means to the opened and closed positions is effected by rotation of the basket in opposite directions relative to its stopped or zero-speed condition. To this end, through the agency of selectively operable actuating means, the positioning means are displaced so as to dispose the valve means in closed position by rotation of the basket in its forward or centrifuging direction and are displaced oppositely so as to dispose the valve means in open position by rotation of the basket in the reverse direction.

Several practical advantages are realized by the utilization of the basket rotation to operate the bottom valve. Especially important is the inherent safety of this arrangement, in that the valve cannot be opened by mistake or by malfunction when the basket is rotating in the forward direction for the loading or the centrifuging operations and, conversely, it cannot be closed inadvertently while the basket is rotating in the reverse direction for the discharging, or unloading, operation. Moreover, an economic advantage is provided by the invention, in that relatively simple clutch means may be' utilized for actuating, or triggering, the movements of the valve means, with the power required for these movements being furnished by the drive of the basket which for other reasons is more than adequate. Also, the actuating parts of the clutch means are not a part of the rotating basket assembly; so they do not require energy to be conducted into it from a special source and do not add to its weight or to dynamic balancing requirements.

The valve means preferably have the form of leaves which are hinged to spokes of the basket bottom structure so that they may be swung downward to a hanging, open position to enable free passage of discharged solids through the bottom openings, with the hinges so disposed relative to the direction of the forward rotation of the basket that during its high speed operation the leaves are urged toward closed position both by the pressure of ambient air and by centrifugal force. In this way safety of the valve mechanism is enhanced in the event of failure of actuation of the valve positioning means to close the leaves; while by virtue of the downward opening movement of the leaves and location of the positioning means below the basket proper there is no obstruction of the working space inside the basket. Further, the motion of the leaves can itself clean the bottom openings so as to prevent solids from building up in them.

In order to effectuate the valve operations, after each period of high speed basket rotation an actuating member mounted independently of the basket, e.g., a nonrotary slip clutch member, is brought into engagement with a mating rotary member provided on valve positioning means which function by being turned to and fro in a limited path relative to the basket bottom structure. The engaged clutch members cause the valve positioning means to be turned relative to the basket so as to open the valve leaves upon rotation of the basket in the reverse direction for a discharging operation. By being kept in sliding engagement those members will then hold the basket in a stable rotating condition during .the operation of a mechanical discharger to dig treated solids out of the basket. Upon the change of the direction of basket rotation which follows the discharging operation, with the clutch members engaged, the leaves are swung upward to their closed position.

According to a further feature of the invention, the valve positioning means include a central rotary member mounted on and turnable in a limited path relative to the hub of the basket bottom structure and link means so connecting this member with the leaves that when the leaves are in closed position the respective link means form toggle joints which prevent the leaves from being forced open by pressure upon their upper sides. By virtue of this locking action the leaves are kept securely closed at any basket speed as long as desired, notwithstanding pressures which may be exerted upon them such as by the impact of material being loaded into the basket or by occasional collapse of a load of material present in the basket.

The foregoing and other objects, features and advantages of the invention will be further apparent from the following detailed description and the accompanying drawings of an illustrative embodiment thereof.

In the drawings:

FIG. 1 is a schematic view in vertical cross-section of a suspended cyclical centrifugal machine provided with the new basket bottom valve mechanism;

FIG. 2 is a top plan view of the basket bottom structure showing the valve leaves in open position;

FIG. 3 is a similar view showing the leaves in closed position;

FIG. 4 is a vertical cross-sectional view of the basket bottom structure, partly in elevation, taken approximately along line 4-4 of FIG. 3;

7 FIG. 5a is a fragmentary bottom plan view showing one of the valve leaves and the related link means in closed position; and

FIG. 5b is a similar view showing the same valve leaf and link means in open position.

The centrifugal machine illustrated in FIG. 1 includes a basket 1 having a substantially cylindrical side wall 2, an annular cap 3 on that wall and an annular bottom wall 4 carried by a bottom ring 5 which is secured to a central hub 6 by four massive, nearly radial spokes 7. The hub 6 is fixed to the foot 8 of a spindle 9' which is suspended in customary manner from a gyratory head (not shown) and is driven by a drive system, indicated schematically at M, under the influence of a sequence control system indicated schematically at 10.

The basket is surrounded by a stationary casing, or curb12 having in its bottom wall a cylindrical skirt 13 surrounding the lower part of the bottom ring 5. The basket side wall 2 in some cases is imperforate but more often is perforated and fitted with screens for filtering liquid away from the solids of an annular charge of granular solids and liquid formed against that wall at the outset of each cycle of operation of the machine.

The drive M and control system may be, for example, of the kinds disclosed in U.S. Pat. No. 2,667,974, whereby the basket is driven in the forward or high speed direction for the loading and centrifuging periods of each operating cycle and, upon being brought to rest, is driven in the opposite or reverse direction to and at a low speed suitable for the operation of a mechanical discharger (not shown) to dig the treated solids out of the basket. As the solids are so removed, they are delivered by gravity through bottom openings 15 provided as sector-shaped spaces between the spokes 7 of the basket bottom structure.

For each of the openings 15 a plate-like closure element or valve leaf is provided, having the form of a segment of a circle defined by the inner surface of a bearing ring 5a which is seated in a notch around the upper inner edge of bottom ring 5. There may be any desired number of spokes, openings and valve leaves in the bottom structure; the illustrated structure comprises four of each. Each leaf 20 has a curved outer edge 21 to mate with the inner surface of bearing ring 5a, a curved inner edge 22 to mate with a flange 6a on hub 6, and a straight edge 23 disposed radially along the left-hand border of the leaf as viewed in FIG. 3, to mate with a radial edge 32 of the hinge plate 30 of an adjacent leaf, which plate is fixed to the upper surface of one of the spokes 7. Each leaf has also, along its right-hand border as viewed in FIG. 3, a hinged edge which in the form shown comprises hinge elements 24 interfitting and connected by a hinge pin 26 with like elements 34 of its own hinge plate 30.

Thus, each leaf is swingable on the nearly radial axis of its hinge pin 26 between a normal closed position as shown in FIG. 3 and FIG. 5a, in which its edges mate with edges of adjacent structures to close and substantially seal off access to one of the bottom openings, and an open position in which it hangs nearly vertically downward from the basket as indicated in FIG. 2 and FIG. 5b and by broken lines in FIG. 4. The drive M of the machine is adapted to rotate the basket in forward direction (clockwise as viewed in FIGS. 2 and 3) for the centrifuging period of each operating cycle. The hinge along the righthand lateral edge of each leaf leads the leaf in the direction of the centrifuging rotation of the basket, with the leaf itself trailing in that direction. Accordingly, if for any reason the basket should be brought to a high speed of rotation when the valve leaves 20 are hanging open, as in FIG. 2, both the centrifugal force resulting on the leaves themselves and the pressure of air ambient to their lower faces will strongly urge them upward toward their closed position. The location of the hinge is reversed if the centrifuging or high speed direction of basket rotation is reversed.

For normal usage of the basket, the movements of the leaves 20 are effected by slow rotation of the basket, according to the direction of such rotation, through the agency of valve positioning means mounted for rotation with the basket bottom structure yet displaceable relative thereto and of actuating means including mated connecting or clutch members which are engageable to cause the valve positioning means and thus the leaves to be displaced relative to the basket by the rotation of the basket.

The valve positioning means of the form shown include a rotary member, or spider, 40 secured to the basket hub 6 yet rotatable to and fro in a limited path relative thereto and a series of circumferentially spaced link means respectively connecting the spider to the leaves 20. The spider is secured to the lower end 43 of a stub shaft 42 mounted for rotation on the axis of the basket in a bearing 44 fixed in the lower end of hub 6. The spider 40 carries an upstanding stop member 41 and comprises four rigid arms 45 which are disposed radially at angular spacings of The stop member 41 coacts with two stops 41a and 41b which protrude downwardly from the lower end of hub 6 at a spacing of approximately so that movement of the spider relative to the hub 6 is confined to a limited path.

Each valve leaf 20 has a rigid arm 28 fixed to its lower side. A rigid link 46 connects each leaf arm 28 with one of the spider arms 45 through universal joints 47 and 48 at the opposite ends of the link. The spider 40 and the link means connecting it with the leaves 20 are so related that when the spider is at the counterclockwise limit of its path of movement relative to the hub 6, as it appears in FIG. 3, the arms 28 and 45 and link 46 of each link means hold the related leaf 20 in closed position. Further, in that disposition of the parts the center of each joint 48 is disposed slightly beyond (to the left of, as viewed in FIG. 3) that radial plane of the structure which contains the center of the related joint 47, so that a toggle is formed which prevents the leaves from being moved out of closed position by pressure applied to their upper side.

On the other hand, a simple angular displacement of the spider 40 relative to the hub 6 in clockwise direction as viewed in FIG. 3, for example, through an angle of approximately 125, brings the spider near the other limit of its path of relative movement, meanwhile drawing the links 46 and leaves 20 downward and inward to an open position such as that of FIG. 2 and FIG. 5b.

As shown further in FIG. 4, the central rotary member, or spider, 40 is formed to comprise a rotary slip clutch member 49 coaxial with the basket. In the illustrated form, this clutch member is a conical surface of female configuration. Located in axial alignment with it is a mating non-rotary slip clutch member 50 carried on the upper end of an upstanding support 51 which is positioned adjustably, as by screw fasteners 52 passed through slots 53, on a vertically movable clutch lever 54. The lever extends between and is movable relative to slotted brackets 14a and 14b fixed to the curb skirt 13 at diametrically opposite locations. A free end 54a of lever 54 extends through'the slot of bracket 140, which serves as a fulcrum. The other end 54b of the lever extends through and beyond the slot of bracket 14b and is coupled by a yoke 55 to the plunger 56 of a two-way air cylinder 57. It is apparent that when air under sufficient pressure is supplied into the lower end of the air cylinder, as through a valve V and supply line 58 under the influence of the sequence control 10, the lever 54 will be raised to a working position in which the clutch members 49 and 50 are engaged. The air pressure is selected at a magnitude which will produce enough friction between the clutch members to cause the power applied for rotation of the basket to displace the spider 40, links 46 and leaves 20 relative to the basket, but which will allow the clutch members to slip when the spider has reached either of the limits of its path of movement relative to the hub 6.

On the other hand, when compressed air is supplied into the upper end of the air cylinder 57, as through valve V and line 59, the lever 54 and non-rotary clutch member 50 are lowered to an idle position at which the mating clutch members are entirely disengaged. Arm 61 of a limit switch 60 may be depressed by the lever end 54b in that idle position of the clutch members, thus closing through the control a circuit which will enable the centrifugal basket to be rotated in forward direction to high speed without restraint by the clutch.

In operation, the mechanism functions as follows: At the end of a normal centrifuging operation the basket is decelerated to a stop and then rotated to and at a low speed in the reverse direction (in this instance, countercloc-kwise, as viewed in FIGS. 2 and 3) for operation of a mechanical discharger to remove treated solids from the basket. At this time air under the selected pressure is delivered into the lower end of cylinder 57, and the non-rotary clutch member 50 is thus moved into working engagement with clutch member 49 on the spider 40. The resulting friction prevents or slows rotation of the spider, causing it to be displaced, relative to the reversely rotating basket, in the direction opposite to that of the basket rotation (in this instance, clockwise as viewed in FIG. 3) until the links 46 have drawn the valve leaves 20 down into their open position. The actuating clutch member can now be either withdrawn or left in working though now slipping engagement with the spider; if the latter course is chosen, member 50 will serve as a stabilizer for the basket during the discharging operation.

The discharging operation is carried out in usual manner, with delivery of the solids by gravity through the basket bottom openings 15. Upon its conclusion the basket is brought to zero speed and then is started in the forward, or high speed, direction of rotation for another cycle of loading and centrifuging operations. At this point, continued engagement or re-engagement of the clutch member 50 with member 49 causes the spider to be returned relative to the basket to its limiting relative position shown in FIG. 3, thus forcing the links 46 and leaves 20 back to their closed and locked position. The actuating clutch member 50 then is withdrawn, as by admitting compressed air into the upper end of cylinder 57 through line 59 and venting the air pressure in line 58 so that the lever 54 will retract clutch member 50 to its lower, idle position. When the clutch member is thus fully disengaged, limit switch 60 is closed. The basket may then be rotated through its high speed operations without any restraint by clutch member 50. Furthermore, the high speed rotation is not accompanied by any danger of the valve leaves 20 being forced open by a pressure applied to their upper side; and even if the toggle action of the links 46 should be omitted, or for any reason should fail to exist, the leaves would still be held in a safely closed position by the centrifugal force and the air pressure which constantly act to urge them closed during the high speed operation of the machine.

What is claimed is: l. A bottom valve mechanism for a cyclical centrifu- V gal basket having in its bottom openings for the delivcry of centrifuged solids from the basket, comprising valve means for closing said openings and movable away from them to an open position, means connected with said valve means and mounted for rotation with said basket yet displaceable angularly relative thereto about the axis thereof for positioning said valve means, and actuating means for causing said positioning means to be displaced angularly relative to said basket so as to dispose said valve means in open position by rotation of said basket in one direction, and to be displaced angularly relative to said basket so as to dispose said valve means in closed position by rotation of said basket in the other direction.

2. A mechanism according to claim 1, said actuating means including a rotary connecting member on said positioning means, a mating connecting member normally disengaged from the structures rotated with said I basket, and means for moving said mating member into clutching engagement with said rotary member so as to restrain the latter against rotation with said basket.

3. A mechanism according to claim 1, said positioning means being turnable in a limited angular path about the axis of said basket, said actuating means comprising a rotary clutch member on said positioning means, a non-rotary clutch member normally disengaged from the structures rotated with said basket, and means for moving said non-rotary clutch member into clutching engagement with said rotary clutch member so as to restrain the latter against rotation with the basket, thereby causing said positioning means to be displaced angularly in one direction relative to said basket so as to move said valve means to closed position by rotation of the basket in the centrifuging direction and to be displaced angularly in the opposite direction so as to 7 move the valve means to open position by rotation of the basket in the reverse direction.

4. A mechanism according to claim 3, said clutch members being mating slip clutch members and said means for moving said non-rotary clutch member being operative to engage the same with said rotary clutch member under a limited pressure sufficient to prevent rotation of said rotary clutch member during displacement of said positioning means yet enabling rotation of said rotary clutch member by slipping thereof relative to said non-rotary clutch member when said positioning means is displacedto either limit of said path.

5. A mechamism according to claim 1, said basket bottom having a bottom ring, a central hub and spokes between said hub and said ring, said openings being spaces between said spokes, said valve means comprising for each of said openings at sector-shaped valve leaf and means hinging each said leaf to one of said spokes for swinging movement of the leaf from closed position to an open position in which it hangs downward from the related spoke, the hinge means of each leaf being disposed along a lateral edge of the leaf from which the leaf trails in the direction of the centrifuging rotation of the basket and said positioning means being responsive centrifugally to rotation of said basket in said direction so that upon such rotation said leaves are urged toward closed position both by the pressure of ambient air and by centrifugal force.

6. A mechanism according to claim 5, each said hinging means being secured to and along the top of the related spoke so as to hinge the related valve leaf on an axis substantially parallel to the center line of the spoke.

7. A mechanism according to claim 1, said basket bottom having a central hub, said valve means comprising a sector-shaped valve leaf for closing each of said openings, said positioning means comprising a rotary spider secured to said hub yet rotatable to and fro in a limited path relative thereto and a series of circumferentially spaced link means respectively connecting said spider to said leaves, and said actuating means comprising a rotary clutch member on said spider, a non-rotary clutch member that mates with said rotary clutch member but normally is disengaged from the structures rotated with said basket and means for moving said nonrotary clutch member into and out of clutching engagement with said rotary clutch member.

8. A mechanism according to claim 7, said clutch members respectively having mating conical surfaces, said surface of said rotary clutch member being coaxial with said basket, and said means for moving said nonrotary clutch member including fluid pressure responsive means for moving the same upward to bring said surfaces into frictional engagement under a predetermined pressure.

9. A mechanism according to claim 8, said means for moving said non-rotary clutch member further including means for retracting the latter away from said rotary clutch member when said valve means have been moved to closed position.

10. A mechanism according to claim 7, each said link means comprising rigid arms respectively on the related valve leaf and said spider, a rigid link, and universal joints respectively connecting the opposite ends of said link to said arms.'

11. A mechanism according to claim 10, the center of the one of said joints that connects said link to the arm on said leaf lying slightly beyond the radial plane containing the center of the other of said joints when said spider is at its valve closing position, so that said leaf is not displaceable from closed position by pressure upon its upper side.

Claims (11)

1. A bottom valve mechanism for a cyclical centrifugal basket having in its bottom openings for the delivery of centrifuged solids from the basket, comprising valve means for closing said openings and movable away from them to an open position, means connected with said valve means and mounted for rotation with said basket yet displaceable angularly relative thereto about the axis thereof for positioning said valve means, and actuating means for causing said positioning means to be displaced angularly relative to said basket so as to dispose said valve means in open position by rotation of said basket in one direction, and to be displaced angularly relative to said basket so as to dispose said valve means in closed position by rotation of said basket in the other direction.

2. A mechanism according to claim 1, said actuating means including a rotary connecting member on said positioning means, a mating connecting member normally disengaged from the structures rotated with said basket, and means for moving said mating member into clutching engagement with said rotary member so as to restrain the latter against rotation with said basket.

3. A mechanism according to claim 1, said positioning means being turnable in a limited angular path about the axis of said basket, said actuating means comprising a rotary clutch member on said positioning means, a non-rotary clutch member normally disengaged from the structures rotated with said basket, and means for moving said non-rotary clutch member into clutching engagement with said rotary clutch member so as to restrain the latter against rotation with the basket, thereby causing said positioning means to be displaced angularly in one direction relative to said basket so as to move said valve means to closed position by rotation of the basket in the centrifuging direction and to be displaced angularly in the opposite direction so as to move the valve means to open position by rotation of the basket in the reverse direction.

4. A mechanism according to claim 3, said clutch members being mating slip clutch members and said means for moving said non-rotary clutch member being operative to engage the same with said rotary clutch member under a limited pressure sufficient to prevent rotation of said rotary clutch member during displacement of said positioning means yet enabling rotation of said rotary clutch member by slipping thereof relative to said non-rotary clutch member when said positioning means is displaced to either limit of said path.

5. A mechamism according to claim 1, Said basket bottom having a bottom ring, a central hub and spokes between said hub and said ring, said openings being spaces between said spokes, said valve means comprising for each of said openings a sector-shaped valve leaf and means hinging each said leaf to one of said spokes for swinging movement of the leaf from closed position to an open position in which it hangs downward from the related spoke, the hinge means of each leaf being disposed along a lateral edge of the leaf from which the leaf trails in the direction of the centrifuging rotation of the basket and said positioning means being responsive centrifugally to rotation of said basket in said direction so that upon such rotation said leaves are urged toward closed position both by the pressure of ambient air and by centrifugal force.

6. A mechanism according to claim 5, each said hinging means being secured to and along the top of the related spoke so as to hinge the related valve leaf on an axis substantially parallel to the center line of the spoke.

7. A mechanism according to claim 1, said basket bottom having a central hub, said valve means comprising a sector-shaped valve leaf for closing each of said openings, said positioning means comprising a rotary spider secured to said hub yet rotatable to and fro in a limited path relative thereto and a series of circumferentially spaced link means respectively connecting said spider to said leaves, and said actuating means comprising a rotary clutch member on said spider, a non-rotary clutch member that mates with said rotary clutch member but normally is disengaged from the structures rotated with said basket and means for moving said nonrotary clutch member into and out of clutching engagement with said rotary clutch member.

8. A mechanism according to claim 7, said clutch members respectively having mating conical surfaces, said surface of said rotary clutch member being coaxial with said basket, and said means for moving said non-rotary clutch member including fluid pressure responsive means for moving the same upward to bring said surfaces into frictional engagement under a predetermined pressure.

9. A mechanism according to claim 8, said means for moving said non-rotary clutch member further including means for retracting the latter away from said rotary clutch member when said valve means have been moved to closed position.

10. A mechanism according to claim 7, each said link means comprising rigid arms respectively on the related valve leaf and said spider, a rigid link, and universal joints respectively connecting the opposite ends of said link to said arms.

11. A mechanism according to claim 10, the center of the one of said joints that connects said link to the arm on said leaf lying slightly beyond the radial plane containing the center of the other of said joints when said spider is at its valve closing position, so that said leaf is not displaceable from closed position by pressure upon its upper side.

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