GB2214241A - Improvements in metering pumps - Google Patents

Abstract

A metering pump is disclosed wherein a piston (2) is axially reciprocable in a pumping chamber (1), inlet (7, 8) and outlet (7a, 8a) ducts leading to respective ends of the pumping chamber from coaxially arranged ports (5, 6 and 5a, 6a) in respective inlet and outlet valving chambers (4, 4a), the coaxially arranged ports of each valving chamber (4, 4a) being alternately closed by valving members (10, 11 and 10a, 11a) slidably mounted on respective control rods (12, 12a). Axial displacement of a control rod away from a central position serves to open one of its two ports (5, 6 and 5a, 6a) while maintaining the other closed, and vice versa. <IMAGE>

Description

"IMPROVEMENT3 IN METERING PUMPS" The present invention relates to closing pumps, and is particularly concerned with a metering pump for use in filling machinery.

Bottle-filling machinery is often supplied with liquids from a storage tank remote from the filling station, and variations in the liquid level in the storage tank give rise to varying hydrostatic pressures at the filling head which can cause inaccuracy in the volume dispensed. To combat this problem, it has been proposed to install a constant-head tank adjacent the filling station, but this is an expensive installation and because it involves a free liquid surface, there is a risk of contamination.

A object of the present invention is to provide a metering pump which can accurately dispense a predetermined volume of a liquid irrespective of variations in the liquid supply pressure to the pump.

According to the present invention, a metering pump suitable for use in a filling machine comprises a cylindrical pumping chamber, a piston sealingly axially reciprocable in the pumping chamber, a pair of inlet ducts leading from repective ends of the pumping chamber to coaxial ports arranged in an inlet valving chamber, a pair of outlet ducts leading from respective ends of the pumping cylinder to coaxial ports arranged in an outlet valving chamber, a respective actuator rod extending through each pair of coaxial ports, and two valve closure members arranged slidably on the actuator rod and resiliently biased towards respective ones of said pair of ports, each valve closure member having an abutment cooperable with a collar on its actuator rod to urge the valve closure member away from its port upon axial movement of the actuator rod.

Preferably the valve closure members are positioned within the inlet and outlet valving chambers respectively, and are resiliently biased apart. Each actuator rod preferably has two collars spaced along its length, two valve closure members being slidably mounted on each actuator rod between the collars thereon.

Most preferably the distance between opposing faces of the collars is slightly greater than the distance between the abutments on the valve closure elements when both valve closure elements are seated in their respective ports.

A pump according to the present invention will now be described in detail, with reference to the accompanying drawings, in which: Figure 1 is a longitudinal central section of the pump assembly during a first dispensing stroke, Figure 2 is a section similar to figure 1 showing the valve operating mechanisms at the mid-point of their changeover travel, and Figure 3 is a longitudinal section similar to figure 1 showing the return dispensing stroke.

Referring now to the drawings, the pump comprises a central cylinder 1 in which a piston 2 is sealingly slidably mounted on a piston rod 3. Piston rod 3 is coupled to a reciprocating drive (not shown) which may be a double-acting air or hydraulic cylinder or may be a cam or crank mechanism driven by a rotating motor.

Positioned adjacent the central cylinder 1 are cylindrical inlet and outlet valving chambers 4 and 4a. Inlet valving chamber 4 has two coaxial axially facing ports 5 and 6 at its ends, port 5 being joined to one end of central cylinder 1 by first inlet duct 7, and port 6 being joined to the other end of central cylinder 1 by second inlet duct 8. Inlet valving chamber 4 also has a main inlet port 9 facing radially away from the central cylinder 1.

Two valve closure members 10 and 11 are positioned within the inlet valving chamber 4, each capable of seating on and closing a respective one of the ports 5 and 6. An axial actuator rod 12 eXt"Rt:. thze the valve loslire member 10 and 11, which are sealingly slidable on the actuator rod 12. A spring 13 is compressed between the valve closure members, urging them apart. Fixed on the actuator rod 12 are two collars 14, 15 which cooperate with abutments 16, 17 on the valve closure members 10, 11 repectively to limit relative movement of the valve closure members 10, 11 on the actuator rod 12. The spacing between the collars 14, 15 is slightly greater than the spacing between abutments 16 and 17 when the valve closure members are both seated on their respective ports 5, 6.

Positioned laterally of the central cylinder 1 opposite the inlet valving chamber 4 is the outlet valving chamber 4a, whose construction is substantially identical to that of the inlet valving chamber 4, and comprises axially opposed ports 5d, 6a, first and second outlet ducts 7a, 8a communicating with respective ends of the central cylinder 1, a main outlet port 9a and valve closure members l0a, lla.

The valve closure members 10a, 11a are controlled by an actuator rod 12a, collars 14a, 15a engageable with abutments 16a and 17a, and a spring 13a as described in relation to the inlet valving chamber 4.

Actuating rods 12, 12a are operated by reciprocating drives, which are shown as double-acting pneumatic cylinders. Equally any other drive may be used, e.g. a solenoid, a hydraulic cylinder, or a mechanical linkage driven by an electric motor.

Operation of the pump is as follows: With the piston 2 at one end of its stroke, as seen in figure 2, actuator rods 12, 12a are urged in opposite directions by their drives to the positions shown in figure 3 so that one port 5 of the inlet valving chamber is closed and the other port 6 opened by closure member 11 being lifted. Communication thus exists between the main inlet port 9 and the right-hand end of the central cylinder as seen in Figure 2. Also, due to the operation of actuator rod 12a, the outlet valving chamber has one port 6a closed and its other port 5a opened, thus providing fluid communication between the interior of the central cylinder 1 and the main outlet port 9a.

By moving the piston 2 leftwards as seen in Figure 3, a quantity of fluid will be expelled from the central cylinder 1 via the first outlet duct 7a, outlet valving chamber 4a and the main outlet port 9a. Simultaneously a substantially equal volume of fluid will be drawn into the central cylinder 1 through the main inlet port 9, inlet valving chamber 4, and second inlet duct 8.

When the piston 2 reaches the left-hand end of its stroke as seen in Figure 3, the actuator rods 12, 12a are urged by their respective drives to their opposite axially displaced positions, shown in figure 1 thus closing ports 6 and 5a, and opening ports 5 and 6a, as shown in figure 1. Piston 2 is then drawn back towards the position shown in figure 2, and the fluid in the central cylinder 1 is expelled via the second outlet duct 8a, port 6a, outlet valving chamber 4a, and main outlet port 9a. Again a substantially equal volume of fluid will be drawn into the central cylinder 1 via the main inlet port 9, inlet valving chamber 4, port 5, and the first inlet duct 7.

It will be noted that, due to the clearance between the collars 14, 15 on the actuator rod 12 and abutments 16, 17, it is impossible for the two valve closure members 10, 11 to be free of their respective ports 5, 6 simultaneously. Thus, during the valve changeover, there is no risk of unmetered seepage through the dispenser due to high hydrodstatic pressures at the main inlet port 9. The arrangement is such that high inlet port pressures merely reinforce the seating of the valve closure members on their respective ports. The presence of the spring 13 ensures that, in the envent of a loss of air pressure in the actuator rod drive, the inlet valve closure members are both returned to their seats and the passage of fluid into the pump is arrested, thus preventing unmetered flows.

It will be appreciated that modifications to the above arrangement are possible, such as linking the two actuator rods 12 and 12a by a lever arrangement and providing a common drive for operating all the valves. Likewise, by adjusting the travel of the piston 2, the volume dispensed at each stroke may be controlled. It is further foreseen that, since the axial reciprocating travel of the piston 2 may be over all of the cylinder 1 or only a part thereof, the reciprocating travel may be asymmetrically axially positioned in the central cylinder. Thus, by providing one adjustable limit for the piston travel and utilising an end of central cylinder 1 as the other limit, a simply. regulatable adjustable meterinq pump may be provided.

Claims (9)

1. A metering pump suitable for use in a filling machine, and comprising a cylindrical pumping chamber1 a piston sealingly axially reciprocable in the pumping chamber, a pair of inlet ducts leading from repective ends of the pumping chamber to coaxial ports arranged in an inlet valving chamber, a pair of outlet ducts leading from respective ends of the pumping cylinder to coaxial ports arranged in an outlet valving chamber, a respective control rod extending through each pair of coaxial ports, and two valve closure members arranged slidably on each control rod and resiliently biased towards respective ones of each said pair of ports, each valve closure member having an abutment cooperable with a collar on its control rod to urge the valve closure member away from its port upon axial movement of the control rod.

2. A metering pump according to Claim 1, wherein the two valving members mounted on each control rod are positioned within one of the valving chambers, and are urged apart by a resilient means into engagement with the ports in the valving chamber.

3. A metering pump according to Claim 2, wherein the two valving members on each control rod are mounted between two axially fixed collars carried by the control rod, the axial distance between the collars being slightly greater than the axial spacing of the abutment surfaces of the valving members.

4. A metering pump according to any preceding Claim, wherein the piston is reciprocated axially in the pumping chamber by means of a fluid-powered actuator.

5. A metering pump according to Claim 4, wherein the actuator is a double acting ram.

6. A metering pump according to any preceding Claim, wherein the control rods are axially reciprocated by means of separate actuators.

7. A metering pump according to any of Claims 1 to 5, wherein the control rods are connected by a linkage so as to be operable simultaneously by a single actuator.

8. A metering pump according to Claim 7, wherein the linkage is a lever joined to the control rods at its respective ends and pivoted at its mid-point.

9. A metering pump substantially as herein described with reference to the accompanying drawings.