GB1590421A - Pump and drive assemblies - Google Patents

Description

(54) IMPROVEMENTS IN AND RELATING TO PUMP AND DRIVE ASSEMBLIES (71) We PICKER CORPORATION, a corporation organised under the laws of the State of New York, United States of America, of 595 Miner Road, Cleveland, Ohio 44143, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - The present invention relates to improvements in pump assemblies and drive assemblies particularly but not exclusively for use in analysis machines of the type escribed in Specification No. 1451449.

In that specification there is disclosed an analysis machine which requires that accurately metered small volumes of liquid be withdrawn from and dispensed into containers. The containers are located in racks in cassettes which are moved from one module of the machine to the next. The racks in a cassette when located in a module are circulated round the cassette past a liquid dispensing or liquid withdrawing head. Each cassette is divided into two compartments and the racks of tubes are arranged in two banks, one in each compartment, and are moved intermittently up each compartment and the front rack in one compartment is moved to the back of the other compartment.

According to the present invention there is provided a pump assembly for liquid comprising a cylinder comprising a cylindrical body having a longtudnal axis and an end member closing one end of said cylindrical body, a piston slidable within said cylindrical body and defining with said body and said end member a pump chamber, said end member defining passage means opening in said pump chamber for liquid flowing to and from said pump chamber, and a valve assembly for connecting said passage means to a selected one of a plurality of inlet/outlet means, said valve assembly including a stationary valve body defining said inlet/outlet means and a moveable valve member fast with said end member for connecting said passage means with said selected one of said inlet/outlet means, said valve member being angularly movable about said axis of said cylindrical body, wherein said valve member is generally frusto-conical, tapering in the direction of said end member, and defines passage means connected to said passage means in said end member and opening in the circumferential surface of said valve member, said valve body is annular and has a corresponding frusto-conical inner circumferential surface in which said inlet/outlet means open and against which said valve member seats.

Preferably said end member provides an end wall closing the one end of said cylinder, said end wall having a generally conical surface, the face of said piston opposite said end wall has a generally conical shape corresponding to that of said surface of said end wall, and said passage means in said end members opens into said pump chamber through an opening in the apex of said conical end wall surface.

Preferably, the end member and the body of the piston are made of PTFE and the cylindrical wall is made of a transparent material, e.g. glass, so that the correct operation of the pump can be visually checked.

Drive means may be provided for reciprocating said piston and moving said valve member in synchronism, said drive means comprising a single motor and two independent cam assemblies for controlling reciprocation of said piston and movement of said valve member respectively.

The present invention will be more fully understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings.

In the drawings: Figure 1 is a vertical section through an embodiment of a pump assembly in accordance with the present invention; Figure 2 is a perspective view of a stop assembly for use with the pump assembly of Figure 1; Figure 3 is a section through part of Figure 1; and Figures 4 and 5 are plan views showing two states of a mechanism for operating the valve assembly associated with the pump assembly of Figure 1.

As shown in Figure 1, the pump assembly comprises a cylinder 1 and a piston 2, one end of the cylinder being closed by an end wall 3 and defining with the piston 2 a pump chamber 4. The piston 2 is provided by a cylindrical member 5, e.g. of glass, closed at one end by an end member 6 providing the end wall 3 for the pump chamber, which end wall is conical. The inlet/ outlet opening 7 for the pump chamber 4 is provided at the apex of the cone in the end member and communicates with an Lshaped passage 8 in member 6. Cylinder 5 is held by rings 9a, 10a, e.g. of PTFE, between two fixed members 9, 10, e.g. of stainless steel, which are bolted together, member 9 being fixed to the framework.

The piston 2 has an end face 11 which is conical and corresponds in shape to the shape of the end wall 3 of the chamber. The piston 2 is fixed to a piston rod 12 which is guided in a bushing 13 through one end of member 10. A vent 14 is provided in member 10.

The end member 6 has a lower cylindrical part 6a which fits into the end of cylinder 5 and seals against the walls of the cylinder, and has an upper conical part 6b which is received in a conical recess in member 9 and is biassed into contact with the recess walls by a spring 15 extending between the member 6 and an end plate 16.

In use, the cylinder 5 is arranged with its axis vertical and end member 6 uppermost. Wall 3 of member 6 and face 11 of piston 2 are shaped as described above so as to encourage the movement of any gas bubbles forming in the pump chamber upwardly to the opening 7. Additionally, the end part of the piston 2 providing face 11 is made of a material, e.g. stainless steel, which inhibits the attachment of gas bubbles thereto. The body of the piston 2 is made of PTFE.

The end of piston rod 12 is received in a sleeve 17 which is retained on the rod by circlips 18. The sleeve 17 is externally threaded and screwed into a threaded bore in a bar or bridge 19 which is attached to rods 20 extending between, and axially slidable relative to, members of the frame and is biassed downwardly by springs 21 around the bars 20. Bridge 19 carries a cam follower 22 (Figure 3) which runs on the periphery of a cam 23 which is rotated by a motor (not shown) about the axis of shaft 24 of the cam. The periphery of the cam is shaped to move the piston 2 from its lowermost to its uppermost positions in the cylinder. At the uppermost position, the cam is provided with a flat surface so that the piston 2 has a short dwell at this time.In operation, the volume of the stroke of the pump, i.e. the effective lowermost position of the piston in the cylinder, is determined by a stop 24 against which the bridge 19 abuts at the end of the required downward travel of the piston. Thus the piston 2 also has a short dwell at its effective lowermost position while the bridge 19 rests on the stop 24 and before the cam follower again contacts the cam 23. The effective lowermost position of the piston may be varied manually or automatically. Preferably a plurality of stops 24a, 24b, 24c . . . (Figure 2) are provided on a rotatable disc 25 which may be rotated manually, for example by providing the shaft of the disc with a knurled knob, or automatically.For auto- matic operation, the periphery of the disc 25 may be toothed and the disc arranged to be in mesh with a gear wheel driven by a stepping motor which is operated when the volume of the pump stroke is to be changed.

The end member 6 forms the body of a valve assembly and is rotated in member 9 about the axis of the cylinder 5 between two positions, shown in Figures 4 and 5, in each of which passage 8 communicates with a radial passage 26 or 27 in member 9. As shown, rotation of member 6 is effected by engagement between a member 28 in the form of a sector of a circle which is fixed to the end of a shaft 29 coaxial with member 5 and fixed to member 6, and a pair of follower rods 30, 31 pivoted by their ends at 32 to a frame member. The rods 30, 31 are parallel and each bears a projection 33 which engages the inner surface 34 of an inverted cup-shaped cam 35.

The inner surface of the cam 35 is part circular with a flat. In operation with the cam 35 rotating, when a projection 33 comes into contact with the flat the follower rod associated therewith is moved towards the axis of the cam to cause the member 28 to pivot. The cam 35 is arranged to be rotated through gearing by the motor driving cam 23 so that the two cams rotate at the same speed. In the preferred embodiment, the shaft 24 of the cam is extended upwardly and provided with a gear which is in mesh with a gear on the shaft of cam 35.

The cams 35 and 23 are so arranged that when the piston reaches either the top of its stroke or the bottom of its stroke and dwells there, during the period of dwell the valve member 6 is rotated from one posi tion to the other position.

There is thus provided a pump assembly which is easy to demount and replace simply by removing the bolts connecting plate 16 to the framework and unscrewing the sleeve 17 from the bridge 19. In re placing the pump, no adjustment of the stop 24 is required since this abuts the bridge 19 and does not act directly on the piston of the pump.

WHAT WE CLAIM IS: - 1. A pump assembly for liquid comprising a cylinder comprising a cylindrical body having a longitudinal axis and an end member closing one end of said cylindrical body, a piston slidable within said cylindrical body and defining with said body and said end member a pump chamber, said end member defining passage means opening in said pump chamber for liquid flowing to and from said pump chamber, and a valve assembly for connecting said passage means to a selected one of a plurality of inlet/outlet means, said valve assembly including a stationary valve body defining said inlet/outlet means and a movable valve member fast with said end member for connecting said passage means with said selected one or said inlet/outlet means, said valve member being angularly movable about said axis of said cylindrical body, wherein said valve member is generally frusto-conical, tapering in the direction of said end member, and defines passage means connected to said passage means in said end member and opening in the circumferential surface of said valve member, said valve body is annular and has a corresponding frusto-conical inner circumferential surface in which said inlet/outlet means open and against which said valve member seats.

2. An assembly as claimed in claim 1, wherein said valve member is integral with said end member.

3. An assembly as claimed in either claim 1 or claim 2, comprising drive means for reciprocating said piston and for moving said valve member in synchronism, said drive means comprising a single motor and two independent cam assemblies for controlling reciprocation of said piston and movement of said valve member respectively.

4. A pump assembly as claimed in claim 3, wherein said cam assembly controlling reciprocation of said piston is adjustable to vary the stroke of said piston.

5. A pump assembly as claimed in either claim 3 or claim 4, wherein said cam assembly controlling reciprocation of said piston is adapted to hold said piston stationary at each end of its stroke during movement of said valve member.

6 An assembly as claimed in any one of the preceding claims, wherein said end member provides an end wall closing the one end of said cylinder, said end wall having a generally conical surface, the face of said piston opposite said end wall has a generally conical shape corresponding to that of said surface of said end wall, and said passage means in said end member opens into said pump chamber through an opening in the apex of said conical end wall surface.

7. An assembly as claimed in claim 6, wherein said face of said piston is made of a material inhibiting the attachement of gas bubbles thereto.

8. An assembly as claimed in claim 7, wherein said cylinder is made of a transparent material, said end member is made of PTFE and said piston comprises a body made of PTFE and a surface part providing said conical face of said piston made of stainless steel.

9. An assembly as claimed in any one of the preceding claims, wherein said end member extends into an end of said cylindrical body.

10. An assembly as claimed in claim 9, wherein said end of said cylindrical member seats on said valve body.

11. An assembly as claimed in any of the preceding claims, wherein said frusto conical valve member is spring biassed into abuttment with said valve body.

12. A pump assembly substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. stop 24 is required since this abuts the bridge 19 and does not act directly on the piston of the pump. WHAT WE CLAIM IS: -

1. A pump assembly for liquid comprising a cylinder comprising a cylindrical body having a longitudinal axis and an end member closing one end of said cylindrical body, a piston slidable within said cylindrical body and defining with said body and said end member a pump chamber, said end member defining passage means opening in said pump chamber for liquid flowing to and from said pump chamber, and a valve assembly for connecting said passage means to a selected one of a plurality of inlet/outlet means, said valve assembly including a stationary valve body defining said inlet/outlet means and a movable valve member fast with said end member for connecting said passage means with said selected one or said inlet/outlet means, said valve member being angularly movable about said axis of said cylindrical body, wherein said valve member is generally frusto-conical, tapering in the direction of said end member, and defines passage means connected to said passage means in said end member and opening in the circumferential surface of said valve member, said valve body is annular and has a corresponding frusto-conical inner circumferential surface in which said inlet/outlet means open and against which said valve member seats.

2. An assembly as claimed in claim 1, wherein said valve member is integral with said end member.

3. An assembly as claimed in either claim 1 or claim 2, comprising drive means for reciprocating said piston and for moving said valve member in synchronism, said drive means comprising a single motor and two independent cam assemblies for controlling reciprocation of said piston and movement of said valve member respectively.

4. A pump assembly as claimed in claim 3, wherein said cam assembly controlling reciprocation of said piston is adjustable to vary the stroke of said piston.

5. A pump assembly as claimed in either claim 3 or claim 4, wherein said cam assembly controlling reciprocation of said piston is adapted to hold said piston stationary at each end of its stroke during movement of said valve member.

6 An assembly as claimed in any one of the preceding claims, wherein said end member provides an end wall closing the one end of said cylinder, said end wall having a generally conical surface, the face of said piston opposite said end wall has a generally conical shape corresponding to that of said surface of said end wall, and said passage means in said end member opens into said pump chamber through an opening in the apex of said conical end wall surface.

7. An assembly as claimed in claim 6, wherein said face of said piston is made of a material inhibiting the attachement of gas bubbles thereto.

8. An assembly as claimed in claim 7, wherein said cylinder is made of a transparent material, said end member is made of PTFE and said piston comprises a body made of PTFE and a surface part providing said conical face of said piston made of stainless steel.

9. An assembly as claimed in any one of the preceding claims, wherein said end member extends into an end of said cylindrical body.

10. An assembly as claimed in claim 9, wherein said end of said cylindrical member seats on said valve body.

11. An assembly as claimed in any of the preceding claims, wherein said frusto conical valve member is spring biassed into abuttment with said valve body.

12. A pump assembly substantially as herein described with reference to the accompanying drawings.