Viscosity Pump

Abstract

A viscosity pump for dosing small quantities of liquid including a rotor and driving shaft, and a housing surrounding the rotor, the cooperating surfaces of rotor or housing being provided with at least one pattern of shallow pumping grooves which communicate on one side with a liquid supply and on the other side with a liquid outlet, the side of the grooves communicating with the outlet being shallower than the rest of the groove.

Description

The invention relates to a viscosity pump for dosing small quantities of liquid, the pump including a rotor provided with a driving shaft as well as a housing surrounding the rotor. The surfaces of the rotor and of the housing facing each other comprise at least one pattern of shallow pumping grooves which communicate at one end with a liquid inlet and at the other end with a liquid outlet.

Viscosity pumps of the above-described type are known and are used as dosing pumps for the accurate dosing of small quantities of liquid, for example, in micro-analysis and in automated chemical analysis. The quantities to be dosed in these cases are very small and cover the range of 30 cm/sec to quantitites smaller than 1cmm/sec. Upon rotating of the rotor, the liquid is transported from the liquid inlet to the liquid outlet through the shallow pumping grooves by the occurring viscous forces. This type of pump gives a continuous, pulse-free supply which is proportional to the number of revolutions of the rotor and independent of the viscosity of the relevant liquid.

These types of pumps may be constructed as cylindrical, conical or flat disk pumps and also as double acting conical or disk pumps.

The pressure variation in the grooves between the liquid inlet and liquid outlet in the relevant pumps has been found to be the same for all the grooves and of little dependence on the distance between the rotor and the housing. This means that in these pumps the rotor is not self-stabilizing, that is to say, if the rotor is moved by some cause or other, no forces occur which counteract this movement. In the case of cylindrical and conical pumps this movement may consist of a tilting and/or eccentric location of the rotor relative to the housing, and in the case of flat disk pumps, mainly of a tilting; in the case of double-acting pumps, a movement of the rotor in the axial direction may occur in addition. Although said movements in the first instance do not influence the supply of the pump, quadratic effects occur in the case of larger movements which influence the quantity of pumped liquid per unit time so that the accuracy of dosing is lost. For a great accuracy of the liquid to be dosed, it is therefore desirable to avoid an occurrence of such disturbing influences.

The viscosity pump according to the invention is characterized in that the part of each of the pumping grooves communicating with the outlet is shallower than the rest of the groove.

This very simple structural measure surprisingly has the result, in the case of variation of the distance between the relevant surfaces, that the pressure in the liquid in the pumping grooves now varies inversely proportionally to the distance, so that a stabilising play of forces on the rotor is obtained and the rotor always assumes the same position relative to the housing, as a result of which the dosing accuracy is always the same.

Since in the viscosity pump according to the invention, the pressure in the liquid is inversely proportional to the distance between the faces in which the patterns of grooves are present, it has now become possible in viscosity pumps in which an axial movement of the rotor and the housing produces a distance variation between the relevant surfaces, to control the liquid pressure supplied by the pump.

For the above purpose, a favourable embodiment of the viscosity pump according to the invention includes the rotor having a surface which encloses an angle with the rotor axis, and the housing having a surface cooperating therewith, and one of the said surfaces comprising a pattern of grooves. The pump is characterized in that the rotor and the housing are movable axially relative to each other, and means are present to exert on the rotor or the housing a control force which may be controllable and is directed opposite to the liquid pressure.

In this viscosity pump, the rotor will automatically assume such a position relative to the housing that the pressure in the liquid is just in equilibrium with the control force. This control force may be exerted, for example, by a spring, a hydraulic or pneumatic pressure, and so on.

A further favourable embodiment of the viscosity pump according to the invention is constructed as a double acting pump; its rotor has two surfaces which enclose an angle with the rotor axis and the housing comprises two surfaces cooperating therewith, and in which each of the said two surfaces of the rotor or the housing is provided with a pattern of grooves. The pump is characterized in that the housing has such a construction that the relevant two surfaces thereof are movable axially relative to each other. In this construction of the pump, the magnitude of the clearance between the rotor and the housing can be varied by varying the distance between the two relevant surfaces which, as described above, produces a variation in the pressure supplied by the pump.

In a further embodiment, one of the said two surfaces forms part of a structural component which is connected to the housing via a flexible diaphragm, means being present to exert pressure on said diaphragm. The pressure exerted on the diaphragm makes equilibrium with the pressure exerted on the housing by the liquid in the pump so that the pressure exerted on the diaphragm is a reference pressure for the pressure of the liquid supplied by the pump. In this manner, a pressure controlled by means of a viscosity pump is obtained with structurally very simple means. The invention will be described in greater detail with reference to the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2 and 3 show diagrammatically the housing, the rotor and the combination thereof, respectively, of a cylindrical viscosity pump.

FIG. 4 is a diagrammatic cross-sectional view of a disk-shaped viscosity pump not drawn to scale

FIG. 5 is a perspective view of the rotor and one of the parts of the housing of the pump shown in FIG. 4,

FIG. 6 shows diagrammatically a conical viscosity pump not drawn to scale.

FIG. 7 shows diagrammatically a disk-shaped viscosity pump of which one of the parts of the housing is axially movable relative to the rotor to control the pressure.

FIG. 8 shows the control principle of FIG. 7 applied to a single-acting conical pump of the type in FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1, 2 and 3 show the housing, the rotor and a cross-sectional view of the combination of housing and rotor, respectively. The rotor is denoted by reference numeral 1. This rotor 1 comprises a shaft 2 which can be coupled to a driving mechanism not shown. The rotor comprises three shallow pumping grooves 3 and three shallow pumping grooves 4. The pumping grooves 3 are separated from each other by dams 6, and the pumping grooves 4 are separated from each other by dams 7. The rotor 1 furthermore comprises a much deeper liquid collecting duct 5 and two liquid supply ducts 8 and 9. Via axial recesses 8', the liquid supply duct communicates with one side of the pumping grooves 3, while the supply duct 9 communicates with one side of the pumping grooves 4 via axially extending recesses 9'. The other side of the pumping grooves 3 and the other side of the pumping grooves 4, respectively, communicate with liquid outlet duct 5 via axial recesses 10 and 11, respectively. The housing furthermore comprises liquid supply apertures 20 and 21 which communicate with the pumping grooves 3 and 4, respectively, and a liquid outlet 13 which communicates with the liquid collecting duct 5.

The rotor 1 fits in the housing 12 with a small amount of play. Upon rotating the rotor in the direction of the arrow as shown, the liquid in the grooves 3 and 4 is forced, by viscous forces, from the inlets 8' and 9' to the outlets 10 and 11. Since the same pressures prevail at the area of the inlets 8' and 9' on the one hand and of the outlets 10 and 11 on the other hand, and the pressure variation in the grooves 3 and 4 is the same for all the grooves, the forces exerted on the rotor will compensate each other as a result of the uniform distribution of the grooves 3 and 4 over the rotor circumference.

It has been found that when the rotor leaves its central position by whatever cause, this has no influence on the pressure variation in the grooves, that is to say, no reaction force will occur which forces the rotor back to its central position. When the deviation becomes too large, however, this causes inaccuracy in the supply of liquid.

In order to prevent this, each of the grooves 3 and 4 comprises a shallower portion 22 on the side where said grooves communicate with the outlets 10 and 11; i.e., the outlet part 10 of the groove is more shallow than the central and inlet parts. It has now been found that as a result of said shallower portions, the pressure in the grooves decreases when the distance between the housing and the rotor increases, while when the distance between the housing and the rotor decreases, the pressure in the grooves increases. The result of this is that the rotor is always forced back to its central position. So in this structurally very simple manner a viscosity pump is obtained having a stable position of the rotor and hence always the same great dosing accuracy. The measure described above for a cylindrical construction of a viscosity pump may be applied with the same advantages to conical and disk-shaped constructions of this type of pumps.

FIG. 4 shows a double-acting disk-shaped pump in which reference numeral 41 denotes a disk-shaped rotor which includes a driving shaft 42. The rotor 41 is surrounded by the parts 43 and 44 of the housing. The surfaces of the parts 43 and 44 of the housing facing the rotor 41 are each provided with a pattern of shallow pumping grooves 45 and 46, respectively, which communicate at one side with the liquid supply chambers 47 and 48, respectively, and communicate on the other side with a common liquid collecting duct 49 which communicates with a liquid outlet 50. The liquid supply chambers 47 and 48 communicate with each other through ducts 51 in the rotor 41, the chamber 48 communicating with a liquid supply duct 52.

The portion 53 of each of the grooves 45, 46 which communicates with the collecting duct 49, is shallower than the rest of the groove. All this is shown in greater detail in the perspective view of the rotor 41 and the part 43 of the housing shown in FIG. 5. The part 44 of the housing is not shown to improve clarity; however, how the portion 53 of each groove becomes gradually shallower in the direction of the collecting duct is shown. Although in this embodiment a gradual transition from the portion 53 to the rest of the groove has been chosen, an abrupt transition may also be used.

Since the pressure in the supply chambers 47 and 48 on the one hand and in the collecting duct 49 on the other hand is the same for all the grooves, the pressure variation, supposing the shallow portion 53 were not present, would be the same in all the grooves independently of the position of the rotor 41 relative to the housing walls. This means that the forces exerted on the rotor in the axial direction are always equal to each other so that no stabilizing effect, that is to say an automatic searching of the central position of the rotor relative to the housing, occurs. In the case of a large deviation from the central position of the rotor, quadratic influences start to influence the dosing accuracy of the pump. In order to prevent this, the shallow portions 53 are provided. These actually ensure that when the play between one side of the rotor and the part of the housing cooperating therewith becomes narrower, the pressure on that side increases while the pressure on the other rotor side decreases as a result of increase of the play. So in this manner an axial force occurs on the rotor which forces it back to its central position, so that a flat viscosity pump is obtained with a stable position of the rotor by the mere position of the shallow portions 53. Tilting if any, of the rotor is also prevented by it.

Although FIG. 4 shows a disk-shaped flat viscosity pump by way of example, it will be obvious that other constructions are also possible. By way of illustration, FIG. 6 shows diagrammatically a conical viscosity pump according to the same principle. In this Figure the parts are referred to by the same reference numerals as in the pump shown in FIG. 4 but with suffix a. A difference is that the liquid supply 52a communicates with only one supply chamber 48a, while on the other side of each pattern of grooves 45a and 46a, respectively, a collection duct 49a is present with which liquid outlet 50a communicates. On the side of the relevant collection duct 49a, each of the grooves 45a and 46a, respectively, is again provided with a shallower portion 53a so that again a stabilizing effect of rotor 41 is obtained which therefore will always be in its central position again.

FIG. 7 finally shows a viscosity pump of the same disk-shaped type as in FIG. 4. For corresponding parts the same reference numerals are used but with suffix b. The only difference with the construction shown in FIG. 4 is that the pattern of grooves 45b is now provided on a structural part 55 which communicates, via a diaphragm 56, with the part 43b of the housing. A chamber 57 is present below the diaphragm 56 and contains liquid the pressure of which can be controlled. For that purpose the space 57 communicates, via a duct 58, with a pressure-supplying control device not shown. The position of the structural part 55 can now be adjusted by means of the liquid in the space 57, a variation of the play between the rotor 41b and the patterns of grooves 45b and 46b thus occurring. This variation will involve a pressure variation namely such that the pressure exerted on the structural part 55 by the liquid in the pump is equal to and opposite to the pressure which is exerted on said part by the liquid in the space 57. So in this manner a viscosity pump is obtained with structurally very simple means and in which liquid can be dosed with a given desirable pressure. Although the reference force on the structural part 55b in this case is obtained hydraulically, this may also be effected, if desirable, mechanically, for example, with spring force, pneumatically, and so on.

FIG. 8 shows diagrammatically how the control principle according to FIG. 7 can also be applied to a single-acting pump. The conically constructed rotor 81 is incorporated in housing 82 which is arranged on a spring 83 the resilience of which can be adjusted by means of an adjusting screw 84. The liquid to be pumped is supplied on the top at 85 and transported to space 87 through the grooves 86 and then to outlet 88. The side of the grooves 86 communicating with the space 87 again comprises a shallower portion. In the liquid pumped to space 87 a pressure will adjust such that an equilibrium of forces is achieved with the force of the spring 83. By adjusting the force of the spring 83 by means of the adjusting screw 84, the desirable liquid pressure can thus be adjusted; it will be obvious that this is associated with a given distance between the rotor 81 and the housing 82. When the pressure in the space 87 becomes higher than corresponds to the force of the spring 83, the housing and the rotor are slightly forced apart as a result of which the distance between the co-operating surfaces becomes larger. As a result of this the internal leak will increase and the pressure will drop until the desirable pressure is achieved.

It will be obvious that in certain circumstances the spring 83 may be replaced by a hydraulic or pneumatic force. It is also possible to exert the force on the rotor instead of on the housing, although this will present a few problems structurally.

Claims

What is claimed is:

1. A viscosity pump for dosing small quantities of liquid, and operable with a source of control fluid comprising, a rotor and drive shaft, a housing that surrounds the rotor, the rotor and housing having at least one pair of adjacent, facing surfaces, which define between them a pattern of continuous shallow pumping grooves comprising an inlet part, a central part, and an outlet part more shallow than the other parts, liquid inlet means communicating with said inlet part, and liquid outlet means communicating with said outlet part, the rotor rotatable and axially movable relative to said housing, whereby the shallowness of said grooves is variable, control means for exerting a selectively, variable axial force on at least one of said housing and rotor members relative to the other, for controlling the shallowness of said grooves, said control means comprising a flexible diaphragm, one side of which supports a part of the housing that defines one of said surfaces, the other side of the diaphragm defining with the housing a chamber, and means communicating said control fluid into said chamber whereby fluid pressure in said chamber moves said diaphragm and thereby varies the shallowness of said grooves.

2. Apparatus according to claim 1 wherein said pair of adjacent surfaces define a generally conical configuration.

3. Apparatus according to claim 1 wherein said pair of adjacent surfaces define two generally conical configurations positioned coaxially with their base parts adjacent.

4. Apparatus according to claim 1 wherein said rotor is a disk, and said pair of adjacent surfaces are in a plane generally normal to the rotor axis.

5. A viscosity pump for dosing small quantities of liquid, and operable with a source of control fluid comprising, a rotor and drive shaft, a housing that surrounds the rotor, the rotor and housing having at least one pair of adjacent, facing surfaces, which define between them a pattern of continuous shallow pumping grooves comprising an inlet part, a central part, and an outlet part more shallow than the other parts, said pair of adjacent surfaces define two generally conical configurations positioned coaxially with their base parts adjacent, liquid inlet means communicating with said inlet part, and liquid outlet means communicating with said outlet part, the rotor rotatable and axially movable relative to said housing, whereby the shallowness of said grooves is variable, control means for exerting a selectively, variable axial force on at least one of said housing and rotor members relative to the other, for controlling the shallowness of said grooves, said control means comprising a flexible diaphragm, one side of which supports a part of the housing that defines one of said surfaces, the other side of the diaphragm defining with the housing a chamber, and means communicating said control fluid into said chamber whereby fluid pressure in said chamber moves said diaphragm and thereby varies the shallowness of said grooves.

6. A viscosity pump for dosing small quantities of liquid, and operable with a source of control fluid comprising, a rotor and drive shaft, a housing that surrounds the rotor, the rotor and housing having at least one pair of adjacent, facing surfaces, which define between them a pattern of continuous shallow pumping grooves comprising an inlet part, a central part, and an outlet part more shallow than the other parts, liquid inlet means communicating with said inlet part, and liquid outlet means communicating with said outlet part, the rotor rotatable and axially movable relative to said housing, whereby the shallowness of said grooves is variable, control means for exerting a selectively, variable axial force on at least one of said housing and rotor members relative to the other, for controlling the shallowness of said grooves.