US20110274563A1

US20110274563A1 - Dosing pump

Info

Publication number: US20110274563A1
Application number: US13/143,210
Authority: US
Inventors: Lior Man; Anton Babushkin
Original assignee: Tefen Manufacture and Marketing Plastic Products 1990 Ltd
Current assignee: Tefen Manufacture and Marketing Plastic Products 1990 Ltd
Priority date: 2009-01-19
Filing date: 2010-01-14
Publication date: 2011-11-10
Also published as: IL196598A0; WO2010082201A1; EP2379885A1

Abstract

A dosing pump comprises an inlet for a solvent, an injection device for an additive, a reciprocating main piston for mixing the solvent with the additive during a suction stroke and for discharging the mixture from an outlet in an evacuation stroke. A divider substantially perpendicular to a rod connected to the main piston separates a main piston housing from a switching device for controlling a main piston stroke direction. The switching device comprises two inlet rotary valve assemblies that are disposed externally to a corresponding inlet aperture bored in the divider when in an opened state and are rotatable about an axis substantially perpendicular to the axis of the main piston. Each of the valve assemblies alternately opens and occludes a corresponding inlet aperture so that solvent flowing through a first inlet aperture performs a suction stroke and solvent flowing through a second inlet aperture performs an evacuation stroke.

Description

FIELD OF THE INVENTION

The present invention relates to the field of pumps. More particularly, the invention relates to an improved dosing pump.

BACKGROUND OF THE INVENTION

Numerous dosing pumps are known in the prior art. Many of these prior art dosing pumps, such as those disclosed in U.S. Pat. No. 4,118,152, U.S. Pat. No. 4,166,411, and U.S. Pat. No. 7,207,260, include a reciprocating piston for effecting the delivery of fluid.
With respect to these prior art pumps, elements of an axially displaceable valve assembly either partially or completely occlude a corresponding passage with which the valve assembly is in communication, thereby increasing the hydraulic resistance of liquid flowing through the passage.
It is an object of the present invention to provide a dosing pump that selectively controls the passage of liquid therethrough without use of axially displaceable valve elements.
It is an additional object of the present invention to provide a dosing pump that generates a significantly increased volumetric flow rate than prior art pumps of similar dimensions.
It is yet an additional object of the present invention to provide a dosing pump that reliably produces a solution of a predetermined concentration, regardless of the volumetric flow rate.
Other objects and advantages of the invention will become apparent as the description proceeds.

SUMMARY OF THE INVENTION

The present invention provides a dosing pump, comprising an inlet for a solvent; an injection device for an additive; a reciprocating main piston and longitudinally disposed rod connected thereto, for mixing said solvent with said additive during a suction stroke and for discharging said mixture from an outlet in an evacuation stroke; a switching device for controlling a main piston stroke direction; and a divider substantially perpendicular to said rod, for separating a main piston housing from said switching device, wherein two inlet apertures for directing the flow of solvent are bored in said divider, wherein said switching device comprises two inlet rotary valve assemblies rotatable about an axis substantially perpendicular to the axis of said main piston, each of said valve assemblies adapted to alternately open and occlude a corresponding inlet aperture and being disposed externally to an inlet aperture in an opened state, solvent flowing through a first inlet aperture adapted to perform said suction stroke and solvent flowing through a second inlet aperture adapted to perform said evacuation stroke.
The switching device further comprises two outlet rotary valve assemblies rotatable about an axis substantially collinear with the axis about which the inlet valve assemblies rotate, each of said outlet valve assemblies adapted to alternately open and occlude a corresponding outlet aperture bored in the divider and being disposed externally to an outlet aperture in an opened state, fluid being discharged from each of said outlet apertures to a dosing pump outlet.
In one aspect, the rod interconnects the main piston and an injection device piston.
The main piston housing comprises a cylindrical wall substantially perpendicular to the divider and defining an annular chamber between the piston housing and a pump housing outer wall, said annular chamber being in fluid communication with a distal variable volume chamber between the main piston and a pump housing terminal surface.
As referred to herein, the term “proximal” means in a direction towards the inlet and outlet apertures, while “distal” means in a direction away from the inlet and outlet apertures.
A first inlet aperture and a first outlet aperture are in communication with the annular chamber and a second inlet aperture and a second outlet aperture are in communication with a proximal variable chamber between the main piston and the divider, solvent admitted to said first inlet aperture adapted to initiate an evacuation stroke while fluid located within said proximal chamber being discharged through said second outlet aperture, and solvent admitted to said second inlet aperture adapted to initiate a suction stroke while solvent located within the distal chamber overflows into the annular chamber and is discharged through said first outlet aperture.
The inlet valve assemblies are located within an inlet flow chamber in communication with the dosing pump inlet and with the first and second inlet apertures, and the outlet valve assemblies are located within an outlet flow chamber in communication with the dosing pump outlet and with the first and second outlet apertures, said inlet and outlet flow chambers being provided with mutually parallel planar walls defining therebetween an additive discharge chamber in communication with the proximal chamber to which additive is discharged from the injection device.
The switching device further comprises mutually longitudinally disposed, parallel and similarly shaped inlet and outlet toggle plates rotatably mounted in the planar wall of the inlet and outlet flow chambers, respectively, said inlet and outlet toggle plates being connected to the inlet and outlet valve assemblies, respectively, and adapted to rotate a predetermined angular distance and in a first rotational direction, so that the first inlet aperture and the second outlet aperture are in an opened state while the second inlet aperture and the first outlet aperture are in an occluded state, or in a second rotational direction so that the second inlet aperture and the first outlet aperture are in an opened state while the first inlet aperture and the second outlet aperture are in an occluded state.
The switching device further comprises a connector for connecting the inlet and outlet toggle plates such that said plates will retain a mutually parallel disposition, a longitudinally displaceable toggle frame, and a dual coiled spring assembly attached to said toggle frame and to each of the toggle plates or to said connector, a change in longitudinal displacement of said toggle plate inducing a corresponding change in a spring caused moment acting on an axis about which the toggle plates rotate.
The axis about which the toggle plates rotate is preferably substantially collinear with the axis about which the valve assemblies rotate.
In one aspect, a tubular carrier support is perpendicularly attached to a corresponding toggle plate and two arms carrying two valve assemblies, respectively, radially extend from said support, said two valve assemblies being angularly spaced by a predetermined value suitable, for alternately closing and occluding two apertures, respectively, bored in the divider.
In one aspect, the spring assembly comprises an a U-shaped head element received in a cavity formed in the toggle frame, two coiled springs, and an element by which each of said springs is attached to a corresponding toggle plate or to the connector.
In one aspect, the toggle frame comprises a head portion and a leg portion substantially perpendicular to said head portion, a first through hole being bored in said leg portion through which the main piston rod interconnected with an injection device piston passes and at least one second through hole being bored in said head portion, said at least one second through hole adapted to receive therein a corresponding longitudinally oriented post, whereby to urge the toggle frame when displaced to maintain a solely longitudinal displacement path.
In one aspect, the main piston rod is configured with an enlarged portion located proximally to the injection device piston, said enlarged portion adapted to contact a wall of the first through hole during a suction stroke, whereby to cause the toggle frame to be proximally displaced.
In one aspect, a longitudinally oriented post extends proximally from the leg portion of the toggle frame, the toggle frame post adapted to be contacted by the main piston during an evacuation stroke, whereby to cause the toggle frame to be distally displaced.
The spring caused moment changes direction during longitudinal displacement of the toggle plate when a spring caused force vector coincides with the toggle plate axis and a corresponding moment arm changes direction.
In one embodiment, the toggle plates are provided with means for repressing a change in their rotational direction. The rotational change repressing means preferably comprises first and second straight edges provided at the toggle frame facing end of the toggle plates for producing a moment counteracting the spring caused moment, a sidewall of the toggle frame head portion adapted to slide along said first edge, following rotation in the first rotational direction of a corresponding toggle plate along the predetermined angular distance, during proximal displacement of the toggle frame and to slide along said second edge, following rotation in the second rotational direction of the corresponding toggle plate along the predetermined angular distance, during distal displacement of the toggle frame.
In one aspect, the divider comprises a distal level and a proximal level, and the cylindrical wall of the main piston housing is configured with an undercut arranged such that a proximal end of the cylindrical wall is separated from said proximal level and an element radially extends from the cylindrical wall to a transitional wall extending between said distal and proximal levels.
In one aspect, the dosing pump further comprises a deactivation switch protrudable from the pump housing outer wall and adapted to prevent operation of the switching device, said deactivation switch being a terminal end of a unitary assembly which comprises first and second cylindrical extension elements having a substantially equal diameter, and a cylindrical connecting element interposed between said first and second extension elements and having a smaller diameter than that of said first and second extension elements, said unitary assembly being axially displaceable upon depression of said deactivation switch to such a distance that an abutment element protruding from the connector will contact said first extension element when the toggle plates are at a predetermined angular disposition at which the first and second inlet apertures and the first and second outlet apertures are in a neutral state.
The dosing pump of the present invention therefore provides at least the following advantages with respect to prior art pumps:

- 1. Significantly reduced hydraulic resistance as the valve assemblies are disposed externally to a corresponding occludable aperture in an opened state.
- 2. Increased main piston housing volume by virtue of an undercut configuration, leading to a lower rate of switching operations, improved reliability without stalling, and reduced fatigue.
- 3. Improved dosing percentage accuracy at low flow rates by virtue of the rotational change repressing means, whereby a rotational change of the toggle plates is repressed from a first angular position of the toggle plates at which the spring caused force vector coincides with the toggle plate axis to a second angular position at which the spring caused force vector is spaced from the toggle plate axis and the occludable apertures abruptly change from an opened state to an occluded state, or vice versa.
- 4. Improved compactness as the toggle frame is longitudinally displaced within the projected area circumscribed by the main piston housing wall.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a perspective, vertical cross sectional view of dosing pump, according to one embodiment of the invention, showing the main piston in a raised position;

FIG. 2 is a top perspective view of the pump of FIG. 1, showing a pump divider when the main piston housing is removed;

FIG. 3 is a top perspective view of the pump of FIG. 1 when the divider is removed, showing the flow of fluid through two fluid chambers with respect to the state of apertures corresponding to a raised main piston position;

FIG. 4 is a perspective, vertical cross sectional view of the pump of FIG. 1, showing the main piston in a lowered position;

FIG. 5 is a top perspective view of the pump of FIG. 1 when the divider is removed, showing the flow of fluid through two fluid chambers with respect to the state of apertures corresponding to a lowered main piston position;

FIG. 6 is a top view of a switching device, according to one embodiment of the invention;

FIG. 7 is a perspective view from the side of a toggle frame used in conjunction with the switching device of FIG. 6;

FIG. 8 is a perspective view of the switching device of FIG. 6 when a dual coiled spring assembly is removed;

FIGS. 9A and 9B are a perspective view of two embodiments, respectively, of a dual coiled spring assembly;

FIG. 10 is a perspective view of a toggle plate used in conjunction with the switching device of FIG. 6;

FIGS. 11A-E illustrate in perspective view various angular positions of the toggle plates of FIG. 10;

FIG. 12 is vertical cross sectional view of one valve assembly and a side view of a second valve assembly used in conjunction with the switching device of FIG. 6;

FIG. 13 is a perspective view of a toggle plate according to another embodiment of the invention;

FIG. 14 is a vertical cross sectional view of a dosing pump, showing a toggle plate according to another embodiment of the invention;

FIG. 15 is a perspective view of a dosing pump, according to another embodiment of the invention;

FIG. 16 is a perspective view from the bottom of the pump of FIG. 15 when the lower cover and injection device are removed, showing a deactivation switch in an extended position;

FIG. 17 is a perspective view from the bottom of the pump of FIG. 15 when the lower cover and injection device are removed, showing a deactivation switch in a retracted position;

FIGS. 18A and 18B are a perspective view from the bottom of the pump of FIG. 15 when the lower cover and injection device are removed, showing a valve assembly in two angular positions, respectively, while a fluid chamber cover is partially shown;

FIG. 19A is a perspective view of a fluid chamber cover assembly;

FIG. 19B is a perspective view from the bottom of the pump of FIG. 15 when the lower cover, injection device and switching device are removed, showing two fluid chambers when the corresponding valve assemblies are removed;

FIG. 20 is a vertical cross sectional view of the pump of FIG. 15, showing a spring caused force vector and moment arm produced by the switching device;

FIG. 21 is a partial vertical cross sectional view of the pump of FIG. 15, showing the spring caused force vector coinciding with a dead point;

FIG. 22 is a perspective view from the top of a two level divider when the piston housing and pump top cover are removed;

FIG. 23 is a perspective, vertical cross sectional view of a dosing pump that employs the two level divider of FIG. 22;

FIG. 24 is a perspective, vertical cross sectional view of a dosing pump, according to another embodiment of the invention;

FIG. 25 is a horizontal cross sectional view of a dosing pump, showing another embodiment of a switching device and a deactivation switch unitary assembly;

FIG. 26 is a perspective view of an injection device, showing the disposition of a sealing element when the injection piston is downwardly displaced;

FIG. 27 is a perspective view of an injection device, showing the disposition of a sealing element when the injection piston is upwardly displaced; and

FIG. 28 is a perspective view of another embodiment of a dosing pump.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is a novel dual piston based dosing pump wherein a solution is prepared during a four stroke cycle. An additive is first drawn during a suction stroke and is introduced to a mixing chamber in an evacuation stroke. In a subsequent suction stroke a solvent is introduced to the mixing chamber to produce the solution, and the mixed solution is discharged from the pump in a subsequent evacuation stroke. A hydraulic engine cylinder is interconnected with an injection device cylinder, and the two cylinders are longitudinally displaced in unison.
An inlet rotary valve assembly, which is connected to a switching device, selectively occludes one of two apertures through which the solvent flows towards the main piston and thereby controls the direction of the piston stroke. An outlet rotary valve assembly, which is also connected to the switching device and is synchronized with the inlet valve assembly, selectively occludes one of two other apertures through which the mixture is discharged.
While prior art dosing pumps comprise an axially displaceable valve assembly that partially or completely occludes a corresponding passage with which the valve assembly is in communication, thereby increasing the hydraulic resistance of liquid flowing through the passage, the valve assemblies of the present invention are disposed externally to the apertures through which fluid can flow. When the direction of the piston stroke is to be changed, the valve assemblies of the present invention rotate a predetermined angular distance about an axis that may be substantially perpendicular to the axis of the piston rod to open one aperture and to occlude another aperture of a corresponding pair of apertures. As an aperture is either completely open or completely occluded, the hydraulic resistance of an aperture that controls the direction of flow of the solvent is significantly reduced with respect to that of prior art dosing pumps, and therefore the volumetric flow rate of the dosing pump of the present invention can be significantly increased with respect to that of the prior art.
As shown in FIGS. 18A and 18B, inlet valve assemblies V1 b and V2 b are attached by carrier arms 91 b and 92 b, respectively, to rotatable carrier support 19 b located within inlet fluid chamber D. In FIG. 18A, valve assembly V1 b is in occluding relation with aperture 72, so that solvent S introduced to fluid chamber D via inlet barrel 62 and opening 66, is forced to flow through open aperture 75. After carrier support 19 b has rotated by means of the switching device, as will be described hereinafter, valve assembly V1 b is released from aperture 72, as shown in FIG. 18B, and valve assembly V2 b is positioned in occluding relation with aperture 75, so that solvent S introduced to fluid chamber D via inlet barrel 62 and opening 66, is forced to flow through the interspace between fluid chamber wall 83 and element 71 to open aperture 72.
FIG. 1 illustrates a dosing pump generally designated by numeral 40, according to one embodiment of the present invention. Dosing pump 40 comprises hydraulic engine 45 and injection device 50, which are interconnected by means of rod 7. Injection device 50 is located below hydraulic engine 45, and is adapted to supply an additive to a mixing chamber located within hydraulic engine 45, as will be described hereinafter. Alternatively, injection device 50 may be located above hydraulic engine 45 in dosing pump 280 illustrated in Fig.
Hydraulic engine 45 comprises a substantially cylindrical base structure 47, to which a solvent, S e.g. water, is admitted via inlet barrel 62 and from which a mixed solution M produced by means of injection device 50 is discharged via outlet barrel 64. Base structure 47 has vertically oriented upper wall 37, intermediate wall 44, and lower wall 49. Intermediate wall 44 is integrally formed with barrels 62 and 64. An upper cover 1 is threadedly engaged with base structure 47 by means of threading T₁provided with upper wall 37. A lower cover 41 is threadedly engaged with base structure 47 by means of threading T₂provided with lower wall 49. Inlet barrel 62 and outlet barrel 64 are generally coaxial, and their central axis is generally horizontally disposed. A vertically displaceable main piston 6 reciprocates within hydraulic engine 45 in response to the direction of liquid flow as controlled by switching device 70.
Base structure 47 has an essentially horizontal divider 67, which divides the main piston housing from the switching device. Divider 67 extends radially inwardly from the inner face 47 of upper wall 37 and that is located slightly above barrels 62 and 64. A closed cylindrical wall 4, with which main piston 6 is sealingly engageable by means of sealing element 5 (FIG. 14), is substantially concentric with base structure upper wall 48 and the inner face 42 of upper cover 1, and extends upwardly from a central portion of divider 67 until terminating slightly below flattened top surface 39 of upper cover 1. Switching device 70 is located below divider 67. If so desired, the main piston housing may have an undercut whereby a lower portion thereof has a smaller dimension than an upper portion thereof, thereby increasing the volumetric flow rate without increasing the outer dimensions of the pump.
Lower cover 41 has an inner portion defined by a substantially planar surface 55 and a radially outer portion 57 disposed below surface 55, to accommodate base structure lower wall 49. Two parallel planar walls 68 and 69 of base structure 47 downwardly extend from divider 67 to lower cover inner portion 55, at a region that is inwardly from cylindrical wall 4. Surface 55 is bored with an aperture through which rod 7 connected to injection device 50 passes.
Hydraulic engine 45 has six fluid transport chambers: (1) variable-volume chamber A within the interior of cylindrical wall 4 and above main piston 6, (2) variable-volume mixing chamber B located between main piston 6 and divider 67, (3) annular chamber C in communication with chamber A and defined by cylindrical wall 4, base structure upper wall 37, upper cover wall 42, and divider 67, (4) inlet fluid chamber D located below divider 67, as defined by base structure lower wall 53 and planar wall 68, and in communication either with chamber B or with chamber C, (5) outlet fluid chamber E located below divider 67, as defined by base structure lower wall 53 and planar wall 69, and in communication either with chamber B or with chamber C, and (6) additive discharge chamber F in communication with mixing chamber B and located below divider 67 and between planar walls 68 and 69.
As shown in FIG. 2, six apertures are bored in divider 67: aperture 61 in communication with mixing chamber B and with additive discharge chamber F and through which rod 7 extends, apertures 72 and 73 inwardly of cylindrical wall 4, apertures 75 and 76 outwardly from cylindrical wall 4, and aperture 120 through which elongated post 99 (FIG. 7) passes. The switching device alternately occludes and opens the pair of apertures 72 and 75 as well as the pair of apertures 73 and 76 such that apertures 73 and 75 will always have the same state, i.e. whether being occluded or opened, and that apertures 72 and 76 will always have the same state
FIG. 3 illustrates inlet chamber D and outlet chamber E, e.g. shown to have an oval shape. Convex walls 81 and 82 defining inlet chamber D extend from base structure lower wall 49 in the vicinity of inlet barrel 62 to planar wall 68, and convex walls 84 and 85 defining outlet chamber E extend from base structure lower wall 49 in the vicinity of outlet barrel 64 to planar wall 69. A tubular wall 86, which is spaced from lower cover inner portion 55, extends downwardly from divider 67 below each of apertures 72, 73, 75, and 76 (FIG. 2). An intermediate planar wall 89 connects two adjacent tubular walls 86.
In FIGS. 1-3, main piston 6 is in a raised position while apertures 73 and 75 are in an opened state and apertures 72 and 76 are in a closed state. Thus solvent S admitted into inlet barrel 62 flows from inlet chamber D to annular chamber C via aperture 75, and then to variable-volume chamber A. Due to the pressure differential between the admitted solvent S and the fluid within chamber B, main piston 6 is urged to be downwardly displaced while performing an evacuation stroke, causing mixture M within chamber B to be discharged via aperture 73, outlet fluid chamber E, and outlet barrel 64.
In FIGS. 4-5, main piston 6 is in a lowered position while apertures 72 and 76 are in an opened state and apertures 73 and 75 are in a closed state. Thus solvent S admitted into inlet barrel 62 flows from inlet chamber D to mixing chamber B via aperture 72. Due to the pressure differential between the admitted solvent S and the fluid within chamber A, main piston 6 is urged to be upwardly displaced while performing a suction stroke, causing the fluid within chamber A to be discharged to annular chamber C, to outlet fluid chamber E via aperture 76, and to outlet barrel 64.
The operation of injection device 50 is illustrated in FIGS. 14, and 24, 26 and 27.
Lower cover 41 has a cylindrical support 22 extending downwardly from surface 55 of the lower cover inner portion and concentric with rod axis I-I. The outer surface of cylindrical support 22 is threadedly connected to an adjustment sleeve 15 by which the dosing percentage is adjusted, and the inner surface of cylindrical support 22 is connected to injection cylinder 14. Latch 16 connects injection cylinder 14 and adjustment sleeve 15. A check valve assembly 18 for preventing backflow of fluid into the additive reservoir is connected and fitted internally to injection cylinder 14.
Main piston rod 7 is provided with an enlarged portion 152 integral with, or keyed to, the lower end thereof. An enlarged portion 152A may be formed with one or more vertically extending grooves 171, e.g. having a concave configuration. Injection piston 17 extends downwardly from enlarged portion 152, and is configured with a vertically extending inner core and with vertically spaced upper and lower circular caps 174 and 176 extending radially outwardly from the inner core. The outer diameter of caps 174 and 176 is greater than that of enlarged portion 152 or 152A. Upper cap 174 is formed with a notch 179. A circular sealing element 28 loosely encircles the inner core and is adapted to contact one of the caps 174 and 176.
Sealing element 28, which has a slightly greater outer diameter than caps 174 and 176, is adapted to sealingly engage the inner wall of injection cylinder 14 during the longitudinal displacement of injection piston 17. During the suction stroke, a vacuum is generated within injection cylinder 14 as injection piston 17 is upwardly displaced and additive H is drawn into the interior of injection cylinder after passing through check valve 18. In response to the upward displacement of injection piston 17, sealing element 28 is forced downwardly until contacting cap 176, as shown in FIG. 27. The drawn additive H therefore remains isolated between check valve 18 and injection cylinder 17.
When injection piston 17 is downwardly displaced during the evacuation stroke as shown in FIG. 26, sealing element 28 is forced upwardly until contacting cap 174. The drawn additive H is therefore able to seep through the clearance between sealing element 28 and cap 176, and then flow to rod enlarged portion 152 or 152A via notch 179. The additive released from injection device 50 is then introduced to additive discharge chamber F, whereupon it flows to mixing chamber B via the aperture 61 formed in divider 67 surrounding rod 7 (FIG. 2).
Alternatively, as shown in FIG. 24, a large area opening 172 is formed in divider 167 radially outwardly from rod 7. Opening 172 is formed above additive discharge chamber F and below mixing chamber B, to reduce the hydraulic resistance to the flow of the additive therethrough.
FIG. 6 illustrates a plan view of switching device 70. Switching device 70 comprises toggle frame 8, mutually parallel and similarly shaped toggle plates 9 a and 9 b from which perpendicularly extend tubular carrier supports 19 a and 19 b, respectively, connector 10 for connecting toggle plates 9 a and 9 b, carrier arms 91-2 a extending from carrier support 19 a, carrier arms 91-2 b extending from carrier support 19 b, valve assemblies V1-2 a and V1-2 b attached to the ends of carrier arms 91 a-b and 92 a-b, respectively, for alternately occluding and opening corresponding apertures formed in divider 67 (FIG. 2), and dual coiled spring assembly 13. Carrier supports 19 a and 19 b preferably have a hollow interior to facilitate connection, e.g. by means of screws, with toggle plates 9 a and 9 b, respectively.
Switching device 70 is configured so that the main piston rod longitudinally extends along axis I-I, toggle plates 9 a-b and carrier supports 19 a-b rotate about axis II-II, dual coiled spring assembly 13 rotates about axis coinciding with the connector facing end of the toggle plates, a post of toggle frame 8 longitudinally extends along axis IV-IV, and toggle frame 8 is longitudinally displaced along axes V-V and VI-VI. Axis II-II is substantially perpendicular to axes I-I, IV-IV, V-V, and VI-VI.
With reference to FIGS. 6, 8 and 11A, a straight arm 91 a and a planar arcuate arm 92 a are carried by support 19 a, and a straight arm 91 b and a planar arcuate arm 92 b are carried by support 19 b. The straight and arcuate arms of a given pair are arranged so as to be angularly spaced by a predetermined value, e.g. 45 degrees. The straight and arcuate arms of a given pair extend radially from the corresponding support, and may be integral therewith, or may be releasably connected thereto. For example, arm 91 b radially extends from support 19 b at connection region 107 b.
FIG. 12 illustrates a front view of valve assembly V1 b and a cross sectional view of a valve assembly V2 b. Valve assemblies V1 b and V2 b comprise a valve head 34 terminating at a proximal end, i.e. in a direction towards an aperture to be occluded by the valve assembly, with a plug element 38, e.g. of a tapered configuration. Valve head 34 is formed with a groove in which is seated O-ring 31, or any other suitable sealing element for preventing passage of fluid through an aperture being occluded. A spring element 33 may be connected to bottom surface 43 of valve head 34 and to spring housing 35 located below valve head 34 such that spring element 33 surrounds stem 59, which extends from valve head bottom surface 43 to below bottom surface 63 of spring housing 35 and terminates with a cap 65. Valve housing 35 is connected to carrier arm 92 b. When carrier support 19 b is rotated in a clockwise direction by means of toggle plate 9 b, as will be described hereinafter, plug element 38 of valve assembly V2 b is urged into tubular wall 86 (FIG. 3) surrounding aperture 75, or directly into aperture 75 as shown in FIGS. 18A-B, so that fluid will be prevented from flowing into annular chamber C (FIG. 2) while cap 65 presses on valve housing 35, thereby compressing spring 33 and providing an improved fluid isolating operation. When carrier support 19 b is rotated in a counterclockwise direction, valve assembly V2 b is released from aperture 75 and valve assembly V1 b is urged into aperture 72. If so desired, a valve assembly may be provided without a spring housing while the carrier arm is connected directly to the valve head.
Dual coiled spring assembly 13A shown in FIG. 9A has a U-shaped head element consisting of an end element 74 and two side elements 78 and 79 connected thereto. Two coiled springs 87 and 88 are connected, and oriented substantially perpendicularly, to side elements 78 and 79, respectively. To coiled springs 87 and 88 are connected parallel leg elements 90 and 92, respectively, which terminate with hook elements 106 a and 106 b that are substantially perpendicular to the axis of the corresponding coiled spring.
Another dual coiled spring assembly 13B shown in FIG. 9B has hook elements 106 a and 106 b that are substantially perpendicular to the axis of coiled springs 123 and 124, respectively. Springs 123 and 124 connected to base elements 128 and 129, respectively, are parallel to, and shorter than, end element 74 of the U-shaped head element.
Alternatively, dual coiled spring assembly 13C shown in FIG. 25 has arcuate hook elements 132 engageable with the periphery of the connector that are substantially collinear with the axis of a corresponding coiled spring 133.
The structure of the switching device will be more readily understood by referring also to FIGS. 7 and 8.
Toggle frame 8 has a rounded T-like configuration, with a head portion 93 and a leg portion 95 extending substantially perpendicularly to head portion 93. Head portion 93 and leg portion 95 have planar top surfaces. Head portion 93 is bored with two apertures 96 and 97 for engaging posts 161 and 162 (FIGS. 17 and 19B), respectively, that are integrally formed with the base structure, extending downwardly from divider 67 and adapted to contact lower cover inner portion 55, as shown in FIG. 14. Alternatively, posts 161 and 162 may be integrally formed with the lower cover, extending upwardly from portion 55 and adapted to contact divider 67. Elongated post 99 protrudes upwardly from top surface 98 of leg portion 95 proximate to head portion 93 and is introducible in a through-hole bored within divider 67. Integrally formed, vertically oriented tubular element 102, which extends downwardly from leg portion 95, is bored with an aperture 101 through which rod 7 (FIG. 1) passes. A triangular brace 143 (FIG. 11A) may connect tubular element 102 to bottom surface 148 of leg portion 95.
Leg portion 95 is hollowed out with a common cavity 105 between each side wall 103 thereof, each side wall 103 being substantially perpendicular to top surface 98 of the leg portion. Cavity 105 is configured such that closed elliptical edge 108 thereof faces tubular element 102 and such that upper wall 111 and lower wall 112 thereof abut sidewall 104 of head portion 93, which is substantially perpendicular to top surface 94 of the head portion. A thin lip element 109 extends slightly towards head portion 93 from elliptical edge 108. Lip element 109, which adjoins cavity 105, is adapted to be engaged by end element 74 of the dual coiled spring assembly, as shown in FIG. 11E, after a side element 78 or 79 (FIG. 9A or 9B) of the latter has been brought to pass through cavity 105 and then to contact a corresponding side wall 103. Alternatively, end element 74 of the dual coiled spring assembly may engage elliptical edge 108.
The toggle frame is adapted to be vertically displaced along posts 161 and 162 (FIG. 19B). As shown in FIGS. 14 and 20, rod 7 is configured with an upper portion 151 and a lower enlarged portion 152 having an outer diameter greater than the outer diameter of upper portion 151 and the inner diameter of tubular element 102 of toggle frame 8 (FIG. 7). Since rod upper portion 151 passes through tubular element 102, rod lower portion 152 will contact lower edge 147 of tubular element 102 during upward displacement of piston 6 and rod 7 connected thereto following passage of solvent S from inlet chamber D to mixing chamber B (FIG. 4). As piston 6 continues to be upwardly displaced, toggle frame 8 will therefore be caused to be upwardly displaced as well. When piston 6 is downwardly displaced following passage of solvent S from inlet chamber D to annular chamber C and then to variable-volume chamber A, as shown in FIG. 1, the piston contacts elongated post 99, causing toggle frame 8 to be downwardly displaced as well.
With reference to FIGS. 8, 10, 11A, 18A and 20, toggle plates 9 a and 9 b have a toggle frame facing end 116, a connector facing end 134, and a central portion 121 interposed between ends 116 b and 134. Each toggle plate is configured with straight edges E1 and E2 at the toggle frame facing end 116 and with arcuate edges 113 and 114 extending from straight edges E1 and E2, respectively, and has mirror symmetry about centerline 115 coincident with apex 117, which adjoins straight edges E1 and E2, and with axis II-II, about which the corresponding toggle plate rotates.
Straight edges E1 and E2 are slightly longer than the vertical dimension of sidewall 104 of toggle frame head portion 93, and are adapted to be in sliding engagement with sidewall 104. The spacing between arcuate edges 113 and 114 is greater in the vicinity of toggle plate central portion 121 than at relatively thin connector facing end 134. Arcuate edges 113 and 114 may have a convex portion 126 in the vicinity of toggle plate central portion 121 and a concave portion 127 between convex portion 126 and connector facing end 134. Connector facing end 134 may be bounded an additional convex portion 137 of arcuate edges 113 and 114.
A plate 136, e.g. rectangular, may protrude from the fluid chamber facing side of a toggle plate. An aperture 131, in which a corresponding hook element 106 a or 106 b (FIGS. 9A and 9B) of a dual coiled spring assembly is pivotally seated, is bored through plate 136 and through connector facing end 134 of the toggle plate. Alternatively, aperture 131 is bored through connector facing end 134 without use of a protruding plate. Hook elements 106 a and 106 b pivot about axis (FIG. 6).
From the fluid chamber facing side of toggle plate central portion 121 protrudes a cylindrical element 141 which is rotatably mounted in a complementary opening formed in planar wall 68 or 69 (FIG. 3) of a corresponding oval fluid chamber. A sealing element such as an O-ring for preventing seepage of fluid from the oval fluid chamber may be mounted on a neck element interposed between cylindrical element 141 and toggle plate central portion 121. A key element 144 for coupling with a complementary element of a carrier support 19 a or 19 b (FIG. 6) protrudes from cylindrical element 141. An aperture 146 coinciding with axis II-II, whereby a carrier support is secured to the corresponding toggle plate by means of a suitable connection means such as a screw, is bored in key element 144.
Connector 10 has a semicircular peripheral surface 118, and is provided with two end plates 119 which are perpendicular to axis III-III. An end plate 119 is adapted to be in abutting relation with connector facing end 134 of a corresponding toggle plate, and is configured with a notch complementary to the shape of plate 136 so that the latter can be seated therein, e.g. by a snap fit. Thus connector 10 retains toggle plates 9 a and 9 b in mutually parallel relation. Connector 10 also has a separating plate 122 e.g. of rectangular cross section, which is substantially perpendicular to the longitudinal axis of surface 118. Separating plate 122 is adapted to separate the two coiled springs of the spring assembly by a predetermined spacing.
As can be appreciated by the above description, the switching device is configured to coact with the dual coiled spring assembly, which is of the compression type. As end element 74 of the spring assembly (FIGS. 9A-B) is engaged with arcuate wall 108, or lip portion 109 thereof, of cavity 105 formed in toggle frame leg portion 95 (FIG. 7) and hook elements 106 a and 106 b of the spring assembly are seated in an aperture 131 (FIG. 10) of a corresponding toggle plate from the interior side thereof, while the two coils are separated by plate 122 of connector 10 (FIG. 8), each coil applies a force from toggle plate end 134 to toggle frame leg portion 95. While toggle frame 8 is vertically displaced, hook elements 106 a and 106 b will pivot about axis and the coils will change their degree of compression as the direction of the spring caused force vector changes as well. Since this force vector varies, the resulting moment which causes the toggle plates to rotate about axis II-II also varies, as will be described hereinafter.
FIG. 20 illustrates the force vector T applied by coiled spring 124 from connector facing end 134 of toggle plate 9 b to arcuate wall 108 of toggle frame 8. In the illustrated disposition of toggle plate 9 b, force vector T is separated from point P coinciding with axis II-II, about which the toggle plate rotates, by an upwardly extending moment arm vector MA, resulting in a clockwise moment. The disposition of toggle plate 9 b does not change until the rotational direction of the moment is reversed by the switching device.
While toggle frame 8 is being upwardly displaced, the direction and magnitude of force vector T and of moment arm MA continuously change. When force vector T coincides with dead point P, as shown in FIG. 21, the length of moment arm MA is essentially zero. Following additional upward displacement of toggle frame 8, the moment arm vector will be downwardly extending, resulting in a counterclockwise moment that is capable of rotating toggle plate 9 b in a similar direction.
FIGS. 11A-E illustrate various angular positions of toggle plates 9 a and 9 b.
In FIG. 11A, toggle frame 8 is in a lowered position. During this position, valve assembly V2 b is occluding aperture 75 and fluid flows from inlet chamber D to mixing chamber B via aperture 72 (FIGS. 4-5), causing main piston 6 to be upwardly displaced. After lower portion 152 of rod 7 (FIG. 20) engages lower edge 147 of tubular element 102, toggle frame 8 is upwardly displaced along axes V-V and VI-VI, as shown in FIG. 11B, while sidewall 104 of head portion 93 slides along edge E1 of toggle plates 9 a and 9 b. Following additional upward displacement of toggle frame 8, the direction of the moment arm acting on axis II-II changes, resulting in a counterclockwise moment M1. Although a counterclockwise moment M1 resulting from the spring caused force vector acts on axis II-II, toggle plates 9 a and 9 b do not rotate since sidewall 104 applies a reactive force to the toggle plates, and the moment resulting from this reactive force, which also acts on axis II-II, has an opposite angular direction than moment M1.
After toggle frame 8 is additionally displaced upwardly above edge E1, as shown in FIG. 11C, the moment resulting from the reactive force ceases to act upon the toggle plates. Since moment M1 is no longer counteracted by the moment resulting from the reactive force, toggle plates 9 a and 9 b are caused to rotate about axis II-II in a counter clockwise direction, as shown in FIG. 11D. Thus valve assembly V2 b is abruptly released from aperture 75 and valve assembly V1 b is abruptly placed in occluding relation with aperture 72, causing fluid to flow from inlet chamber D to annular chamber C via aperture 75 and to cause piston 6 to be downwardly displaced (FIGS. 1-2). The counterclockwise rotation of toggle plates 9 a and 9 b is limited by means of the reactive force applied by divider 67, or by tubular 86 (FIG. 3) extending therefrom, onto valve assembly V1 b when the latter is in occluding relation with aperture 72. In FIG. 11E, toggle frame 8 is downwardly displaced along axes V-V and VI-VI while sidewall 104 slides along edge E2 of toggle plates 9 a and 9 b. After toggle frame 8 is downwardly displaced below edge E2, toggle plates 9 a and 9 b are caused to be rotated in a clockwise direction by moment M2 until returning to the disposition shown in FIG. 11A.
If so desired, a toggle plate 149 shown in FIG. 13 or a toggle plate 159 shown in FIG. 14 may be provided with a completely arcuate toggle frame facing end 146, i.e. without straight edges. The toggle plate of these embodiments is not adapted to contact toggle frame 8. Toggle plate 159 may be provided with a square connector facing end 154.
FIGS. 13 and 25 illustrate another embodiment of a switching device 310. Toggle plates 149 a and 149 b have a proximal edge 113 and distal edge 114 that extend from toggle frame facing end 146, and a connector facing end 142 that terminates with concave edge 313. C-shaped socket 316 protrudes from the fluid chamber facing side of connector facing end 142 such that its inner wall coincides with concave edge 313. Connector 320 is tubular, and has two terminal tubular ends that are received by a friction fit in socket 316 of toggle plates 149 a and 149 b, respectively, to ensure that the latter remain in mutually parallel relation. Arcuate hook elements 132 of dual coiled spring assembly 13C engage connector 320, so that the springs 133 will be tensed and to thereby cause the toggle plates to rotate.
FIGS. 15-25 illustrate another embodiment of the invention wherein a dosing pump 240 is provided with a deactivation switch 245, for preventing operation of the hydraulic engine. Deactivation switch 245 protrudes from intermediate wall 244 of the base structure in the vicinity of outlet barrel 64.
Deactivation switch 245 is a terminal end of a unitary assembly 243 (FIG. 25) that comprises cylindrical extension elements 246 and 249 having a substantially equal diameter, and cylindrical connecting element 248 interposed between extension elements 246 and 249. Extension elements 246 and 249 are supported by housings 241 and 242, respectively.
Connecting element 248 has a smaller diameter than extension elements 246 and 249, so that when toggle plates 9 a and 9 b rotate, abutment element 255 attached to a central portion of connector peripheral surface 118 will not contact connecting element 248, as shown in FIG. 16. However, when deactivation switch 245 is depressed, as shown in FIG. 17, elements 246 and 248 are shifted towards housing 242, resulting in the protrusion of activation switch 251 from intermediate wall 244, so that abutment element 255 will contact element 246. Additional angular displacement of toggle plates 9 a and 9 b is prevented following contact between abutment element 255 and extension element 246. The dimensions of extension element 246 and abutment element 255 are selected such that toggle plates 9 a and 9 b will be immobilized at a predetermined angular disposition by which all of the occludable apertures are in a neutral state, i.e. not fully opened and not fully occluded. Thus the solvent will be introduced to the dosing pump via both of the inlet apertures and will be discharged, possibly as a mixture with the additive, via both of the outlet apertures. When it is desired to reactivate the dosing pump, activation switch 251 is depressed, and unitary assembly 243 is shifted towards housing 241. Deactivation switch 245 and activation switch 251 may be provided with a capped end 252 for contacting outer surface 239 of housings 241 and 242, respectively, thereby limiting the axial displacement of unitary assembly 243 in each direction.
Alternatively, a sphere 12 which is biased inwardly by means of spring actuated device 11 (FIG. 14) may be employed to immobilize toggle plates 159 at a predetermined angular disposition by which all of the occludable apertures are in a neutral state.
In this embodiment, fluid chambers D and E downwardly extend from divider 264 to a height above lower cover surface 55 (FIG. 1). Posts 161 and 162 with which the toggle frame is engaged also extend downwardly from divider 264. Fluid chambers D and E may be covered by virtue of the spacing between bottom edge 259 of the fluid chambers and lower cover surface 55. When covers 256 and 257, e.g. of oval shape, are pressed onto bottom edge 259 of fluid chambers D and E, respectively, the corresponding carrier supports become stabilized.
A cover assembly 266 is illustrated in FIG. 19A. Cover assembly 266 comprises oval cover 256 or 257, and mutually parallel plates 262 and 267 longitudinally extending from the underside of the cover towards divider 264. Extensions 276-278 radially protruding from cover 256 are adapted to be received by a friction fit in complementary recesses 281-283 formed in bottom edge 259 of a fluid chamber (FIG. 19B). Arcuate openings 263 and 267, e.g. semicircular, are formed in plates 262 and 267, respectively, such that their open portion faces divider 264. The length of plates 262 and 267 is selected to enable the wall of openings 263 and 267, respectively, to engage the corresponding tubular carrier support 19 a or 19 b (FIG. 8) when the cover is pressed onto bottom edge 259 of a fluid chamber. The carrier support is therefore rotatably mounted in arcuate openings 263 and 267, which serve as bearing elements, while ensuring that the valve assemblies will rotate about axis II-II (FIG. 11D).
Alternatively as shown in FIG. 18B, a cover assembly may comprise a cover element 77, which is only partially illustrated, provided with a single arcuate opening, e.g. semicircular, for engaging the carrier support, and an additional bearing element 71 provided with a single arcuate opening for engaging the carrier support. Bearing element 71 may be fixedly connected to cover element 77 by any means well known to those skilled in the art.
The employment of openable fluid chambers also facilitates assembly of the valve assemblies. A concave recessed portion 273 is formed within the divider 264 of each of fluid chambers D and E, to accommodate the placement therein of a corresponding tubular carrier support 19 (FIG. 8). After a carrier support 19 is seated in the corresponding recessed portion 273, an arm 91 carrying valve assemblies V1 and V2 can be attached to the corresponding carrier support 19 at a connection region 107 (FIG. 11A). When a fluid chamber is uncovered, the mounting of a cylindrical element 141 (FIG. 10) of a toggle plate 9 within opening 275 formed in a planar wall of a corresponding fluid chamber or the connection of a carrier support 19 with a toggle plate 9 by means of key element 144 is simplified.
Another feature of this embodiment is that the piston housing is provided with an undercut such that the proximal end thereof is separated from the divider. The diameter of the piston housing can advantageously be increased without interfering with the passage of fluid through the two outwardly disposed apertures bored in the divider. The capacity of the dosing pump is therefore increased, resulting in a considerably greater volumetric flow rate, without increasing its outer dimensions.
Since the undercut configuration provides an increased volume of the variable volume chambers A and B, the switching device can be adjusted to effect a lower rate of switching operations than prior art dosing pumps while generating a selected mixture at a desired volumetric flow rate. Due to their relatively high rate of switching operations, prior art dosing pumps tend to experience periods of stalling since their piston is subject to relatively high inertia loads. The main piston of dosing pump 240 of the present invention, in contrast, is subject to lower inertia loads than one associated with prior art pumps as a result of its lower rate of displacement. Consequently, dosing pump 240 can operate reliably without stalling. An additional advantage of a lower rate of switching operations is that the switching device, and particularly the dual coiled spring assembly, experiences a reduced level of wear and fatigue.
As shown in FIG. 20, the piston housing has a cylindrical wall 287 and an extension element 291 substantially perpendicular to, and extending radially inwardly from the proximal end of, wall 287 to distal divider level 167. A support element 294 proximally extends from extension element 291. Alternatively, an undercut piston housing may be configured without a support element, but rather with a chamfered portion 295 at the proximal end of cylindrical wall 287 and with one or two extension elements 297 extending radially inwardly from chamfered portion 295, as shown in FIGS. 23 and 25.
The undercut configuration is made possible by providing the base structure with a two leveled divider. As shown in FIGS. 22 and 23, a transitional wall 197 substantially concentric with base structure upper wall 268 extends distally from proximal divider level 177 to distal divider level 167. Occludable apertures 232, 233, 235 and 236 are bored in proximal divider level 177, and are positioned such that apertures 235 and 236 are located outwardly from transitional wall 197 while apertures 232 and 233 are located inwardly from wall 197. Apertures 232 and 235 are in communication with the inlet flow chamber D, and apertures 233 and 236 are in communication with outlet chamber E. To allow the inwardly located apertures to communicate with mixing chamber B, recessed portions 201 and 202 are formed in the vicinity of apertures 232 and 233, respectively, extending from proximal divider level 177 to distal divider level 167. Extension element 297 of cylindrical wall 287 is therefore able to abut and be connected to transitional wall 197 while apertures 232 and 233 are able to communicate with annular chamber C.
A two leveled divider also allows toggle plates 9 a and 9 b to freely rotate without contacting the divider while the valve assemblies connected therewith are able to open or occlude the corresponding occludable apertures. Apertures 302 and 307 through which main piston rod 7 and toggle frame post 99 pass, respectively, are also bored in distal divider level 167. Large area opening 172 in communication with additive discharge chamber F and mixing chamber B is also formed in distal divider level 167.
FIG. 28 illustrates a dosing pump 330 that employs hydraulic engine 345, a lower injection device 50, and an upper injection device 350. A single rod may interconnect the upper injection piston, main piston, and lower injection piston, or alternatively, a separate rod may connect the main piston to the upper injection cylinder. An additive is first drawn from the upper injection device during proximal displacement of the main cylinder and is introduced to the distal variable volume chamber when the main cylinder is distally displaced.
If so desired, a dosing pump may employ an upper injection device 350 exclusively. Alternatively, the main piston rod may be horizontally disposed or disposed at any other desired orientation.
While some embodiments of the invention have been described by way of illustration, it will be apparent that the invention can be carried out with many modifications, variations and adaptations, and with the use of numerous equivalents or alternative solutions that are within the scope of persons skilled in the art, without departing from the spirit of the invention or exceeding the scope of the claims.

Claims

1. A dosing pump, comprising:

a. an inlet for a solvent;

b. an injection device for an additive;

c. a reciprocating main piston and longitudinally disposed rod connected thereto, for mixing said solvent with said additive during a suction stroke and for discharging said mixture from an outlet in an evacuation stroke;

d. a switching device for controlling a main piston stroke direction; and

e. a divider substantially perpendicular to said rod, for separating a main piston housing from said switching device, wherein two inlet apertures for directing the flow of solvent are bored in said divider,

wherein said switching device comprises two inlet rotary valve assemblies rotatable about an axis substantially perpendicular to the axis of said main piston, each of said valve assemblies adapted to alternately open and occlude a corresponding inlet aperture and being disposed externally to an inlet aperture in an opened state, solvent flowing through a first inlet aperture adapted to perform said suction stroke and solvent flowing through a second inlet aperture adapted to perform said evacuation stroke.

2. The dosing pump according to claim 1, wherein the switching device further comprises two outlet rotary valve assemblies rotatable about an axis substantially collinear with the axis about which the inlet valve assemblies rotate, each of said outlet valve assemblies adapted to alternately open and occlude a corresponding outlet aperture bored in the divider and being disposed externally to an outlet aperture in an opened state, fluid being discharged from each of said outlet apertures to a dosing pump outlet.

3. The dosing pump according to claim 1, wherein the rod interconnects the main piston and an injection device piston.

4. The dosing pump according to claim 2, wherein the main piston housing comprises a cylindrical wall substantially perpendicular to the divider and defining an annular chamber between the piston housing and a pump housing outer wall, said annular chamber being in fluid communication with a distal variable volume chamber between the main piston and a pump housing terminal surface.

5. The dosing pump according to claim 4, wherein a first inlet aperture and a first outlet aperture are in communication with the annular chamber and a second inlet aperture and a second outlet aperture are in communication with a proximal variable chamber between the main piston and the divider, solvent admitted to said first inlet aperture adapted to initiate an evacuation stroke while fluid located within said proximal chamber being discharged through said second outlet aperture, and solvent admitted to said second inlet aperture adapted to initiate a suction stroke while solvent located within the distal chamber overflows into the annular chamber and is discharged through said first outlet aperture.

6. The dosing pump according to claim 5, wherein the inlet valve assemblies are located within an inlet flow chamber in communication with the dosing pump inlet and with the first and second inlet apertures, and the outlet valve assemblies are located within an outlet flow chamber in communication with the closing pump outlet and with the first and second outlet apertures, said inlet and outlet flow chambers being provided with mutually parallel planar walls defining therebetween an additive discharge chamber in communication with the proximal chamber to which additive is discharged from the injection device.

7. The dosing pump according to claim 6, wherein the switching device further comprises mutually longitudinally disposed, parallel and similarly shaped inlet and outlet toggle plates rotatably mounted in the planar wall of the inlet and outlet flow chambers, respectively, said inlet and outlet toggle plates being connected to the inlet and outlet valve assemblies, respectively, and adapted to rotate a predetermined angular distance and in a first rotational direction, so that the first inlet aperture and the second outlet aperture are in an opened state while the second inlet aperture and the first outlet aperture are in an occluded state, or in a second rotational direction so that the second inlet aperture and the first outlet aperture are in an opened state while the first inlet aperture and the second outlet aperture are in an occluded state.

8. The dosing pump according to claim 7, wherein the switching device further comprises a connector for connecting the inlet and outlet toggle plates such that said plates will retain a mutually parallel disposition, a longitudinally displaceable toggle frame, and a dual coiled spring assembly attached to said toggle frame and to each of the toggle plates or to said connector, a change in longitudinal displacement of said toggle plate inducing a corresponding change in a spring caused moment acting on an axis about which the toggle plates rotate.

9. The dosing pump according to claim 8, wherein the axis about which the toggle plates rotate is substantially collinear with the axis about which the valve assemblies rotate.

10. The dosing pump according to claim 9, wherein a tubular carrier support is perpendicularly attached to a corresponding toggle plate and two arms carrying two valve assemblies, respectively, radially extend from said support, said two valve assemblies being angularly spaced by a predetermined value suitable for alternately closing and occluding two apertures, respectively, bored in the divider.

11. The dosing pump according to claim 8, wherein the spring assembly comprises an a U-shaped head element received in a cavity formed in the toggle frame, two coiled springs, and an element by which each of said springs is attached to a corresponding toggle plate or to the connector.

12. The dosing pump according to claim 8, wherein the toggle frame comprises a head portion and a leg portion substantially perpendicular to said head portion, a first through hole being bored in said leg portion through which the main piston rod interconnected with an injection device piston passes and at least one second through hole being bored in said head portion, said at least one second through hole adapted to receive therein a corresponding longitudinally oriented post, whereby to urge the toggle frame when displaced to maintain a solely longitudinal displacement path.

13. The dosing pump according to claim 12, wherein the main piston rod is configured with an enlarged portion located proximally to the injection device piston, said enlarged portion adapted to contact a wall of the first through hole during a suction stroke, whereby to cause the toggle frame to be proximally displaced.

14. The dosing pump according to claim 13, wherein a longitudinally oriented post extends proximally from the leg portion of the toggle frame, the toggle frame post adapted to be contacted by the main piston during an evacuation stroke, whereby to cause the toggle frame to be distally displaced.

15. The dosing pump according to claim 14, wherein the spring caused moment changes direction during longitudinal displacement of the toggle plate when a spring caused force vector coincides with the toggle plate axis and a corresponding moment arm changes direction.

16. The dosing pump according to claim 15, wherein the toggle plates are provided with means for repressing a change in their rotational direction.

17. The dosing pump according to claim 16, wherein the rotational change repressing means comprises first and second straight edges provided at the toggle frame facing end of the toggle plates for producing a moment counteracting the spring caused moment, a sidewall of the toggle frame head portion adapted to slide along said first edge, following rotation in the first rotational direction of a corresponding toggle plate along the predetermined angular distance, during proximal displacement of the toggle frame and to slide along said second edge, following rotation in the second rotational direction of the corresponding toggle plate along the predetermined angular distance, during distal displacement of the toggle frame.

18. The dosing pump according to claim 4, wherein the divider comprises a distal level and a proximal level, and the cylindrical wall of the main piston housing is configured with an undercut arranged such that a proximal end of the cylindrical wall is separated from said proximal level and an element radially extends from the cylindrical wall to a transitional wall extending between said distal and proximal levels.

19. The dosing pump according to claim 8, further comprising a deactivation switch protrudable from the pump housing outer wall and adapted to prevent operation of the switching device, said deactivation switch being a terminal end of a unitary assembly which comprises first and second cylindrical extension elements having a substantially equal diameter, and a cylindrical connecting element interposed between said first and second extension elements and having a smaller diameter than that of said first and second extension elements, said unitary assembly being axially displaceable upon depression of said deactivation switch to such a distance that an abutment element protruding from the connector will contact said first extension element when the toggle plates are at a predetermined angular disposition at which the first and second inlet apertures and the first and second outlet apertures are in a neutral state.