Drive for a pair of metering pumps

A pair of metering pumps are fixedly supported on a mounting frame and are driven in tandem by a reciprocable thrust mechanism for driving the piston or cylinder element of the pump. The thrust mechanism is movable transversely to the reciprocating direction and is supported on a frame. Two levers have respective ends linked to the thrust mechanism and to the frame, respectively. One of the reciprocable pump elements is suspended on a respective lever whereby reciprocation of the thrust mechanism causes corresponding reciprocation of the suspended pump element. The levers are held stationary with respect to the thrust mechanism and the suspension of the reciprocable pump elements holds them stationary with respect to the mounting frame.

The present invention relates to a drive for a pair of pumps for metering 
liquid to paste-like materials. 
Reciprocating metering pumps are used for accurately dosing liquids, 
including highly viscous liquids up to a pasty consistence, such as 
synthetic resins. Particularly in chemical reaction processes, it is 
necessary to deliver reactants continuously or batch-wise in accurately 
predetermined ratios and it is desirable to provide for stepless 
adjustment of the delivery rate of the metering pumps. 
Tandem drives for a pair of metering pumps have been proposed wherein the 
reciprocable piston rods of the pumps are connected to a lever whose pivot 
is arranged between the pumps. The pivot may be moved laterally towards 
the metering pump mounted remote from the drive. The metering ratio is 
thus adjusted by changing the length of the reciprocating stroke of the 
lever. This arrangement has the disadvantage that the two metering pumps 
operate in opposed stages, i.e., when one of the pumps takes the material 
in, the other pump delivers the material. This leads to dosing errors. 
Furthermore, the adjustment range is limited since only the stroke of one 
of the pumps may be varied. This requires an increased number of metering 
pumps with different cylinder diameters. Furthermore, this arrangement has 
the considerable disadvantage that the piston rods are subjected to radial 
stresses, causing wear on the pistons and gaskets, and making the use of 
pump cylinders with small diameters structurally difficult. 
Attempts have been made to reduce the effect of radial stresses by mounting 
the pumps movably to enable them to be laterally displaced. In this case, 
the material delivery conduits must be flexible and, if these conduits are 
to be heated, this causes problems. Also, it is difficult to find 
materials for flexible tubular conduits which are not readily corroded and 
remain flexible for an extended period of time. Also, considering the fact 
that viscous liquids and pastes are often delivered to the pumps under 
relatively high pressures, flexible tubular conduits are subject to 
bursting, thus being a possible source of accidents. For these and other 
reasons, rigid pipes are preferred for the delivery of liquids to metering 
pumps, which requires the pumps to be stationary. 
Another pump drive comprises a lever whose pivot is on the side remote from 
the drive. This arrangement comprises single and double lever systems, the 
latter systems enabling the use of more than one metering pump 
side-by-side. In these drives, radial stresses are imparted to the pump 
pistons or the pumps are laterally movable, each case producing the 
disadvantages indicated hereinabove. In all these known drives, the total 
throughput is reduced proportionally to a change of the delivery ratio 
from a 1 : 1 equilibrium between the two pumps. 
Pump drives have also been used with a lever system in which the levers are 
arranged in scissors fashion. These known systems are very complex, 
however, and accordingly expensive, the adjacent levers exerting 
assymmetric forces causing excessive wear. The opposing radial movements 
must be absorbed by special straps or the like. 
It is the primary object of this invention to provide a drive for a pair of 
pumps for metering liquid to paste-like materials, which are simple to 
build, relatively small in size and exhibit great adjustability of the 
dosing ratios of the materials delivered by the pumps. 
The above and other objects are accomplished in accordance with the 
invention with a drive which comprises a reciprocable thrust mechanism for 
driving one of the pump elements, i.e., the piston rod or the cylinder, 
for reciprocation in a first direction, the thrust mechanism being 
arranged for movement in relation to the mounting frame which fixedly 
supports a pair of pumps in spaced relationship in a second direction 
transverse to the first direction. A frame supports the thrust mechanism 
and two levers have respective ends linked to the thrust mechanism and to 
the frame, respectively. One of the pump elements is suspended on a 
respective one of the levers whereby reciprocation of the thrust mechanism 
causes corresponding reciprocation of the suspended pump elements, the 
levers are laterally stationary with respect to the thrust mechanism and 
the suspension is laterally stationary with respect to the mounting frame. 
Such a drive arrangement has the considerable advantage that a large 
adjustment range may be obtained with a small and simple structure. 
Advantageously, the metering pumps are stationary in this arrangement, 
making it possible to supply them with rigid piping. The drive can be used 
selectively for continuous or batch-wise operations. Extremely small 
diameter pumps may be used since the pistons are not subjected to radial 
stresses. Furthermore, while the metering ratios may be varied widely, the 
throughput of the pumps remains almost unchanged. Thus, a single pair of 
pumps may be used over a wide range and this range may be further 
increased by the use of pumps with other diameters adapted to the stroke 
ratios of the lever system. Since the thrust mechanism is displaceable 
transversely to the reciprocating direction of the pump pistons, radial 
stresses are eliminated by simply sliding the thrust mechanism in the 
transverse direction when pumps with very small diameters are used. 
Instead of slidingly mounting the thrust mechanism, push rods and like 
means may be used for the purpose of displacing the same.

Referring now to the drawing, there is shown reciprocable thrust mechanism 
1 which is shown, by way of example, as a cylinder containing reciprocable 
piston rod 2 driven in the cylinder by compressed air. The piston rod 
carries connecting part 3 at its outer end and stroke limiting device 9 is 
mounted atop the cylinder of the thrust mechanism to limit the 
reciprocating stroke of the mechanism. In the illustrated embodiment, 
mounting plate 4 of a frame including lateral supports 5 fixedly supports 
thrust mechanism 1. Two levers 6 and 7 have respective ends linked to 
connecting part 3 of the thrust mechanism and to lateral supports 5 of the 
thrust mechanism supporting frame, respectively. Preferably, the lever 
ends are mounted for universal motion, for instance, by ball-and-socket 
joints mounting the inner ends of the levers in connecting part 3 while 
their outer ends 8 are similarly mounted in lateral supports 5. In this 
manner, reciprocation of piston rod 2 of pneumatically operated thrust 
mechanism 1 will cause levers 6 and 7 to be moved from a neutral position, 
shown in full lines in FIG. 2, to two end positions shown in chain-dotted 
lines. Ends 8 of the levers are held against reciprocating movement in 
lateral supports 5. Stroke limiting device 9 may be adjusted when the 
pumping unit is used for the batch-wise delivery of materials so as to 
determine the delivered amount of materials in each batch. 
The pump unit comprises a pair of metering pumps 11 and 12 each of which 
comprises a piston rod element and a cylinder element, one of the pump 
elements being reciprocable in relation to the other. While the 
illustrated embodiment shows the reciprocable element to be the piston 
rod, it will be obvious to those skilled in the art that the operation 
would be identical if the cylinder were reciprocable and the piston rod 
were held stationary. A mounting frame fixedly supports the pumps, i.e., 
the stationary element thereof, in spaced relationship, the mounting frame 
being comprised of a pair of mounting plates 13 and 15 substantially 
parallel to each other and two guide columns 14 fixedly interconnecting 
the mounting plates. 
Mounting plate 15 carries guide rails 10 wherebetween mounting plate 4 of 
the thrust mechanism frame is mounted for movement in relation to the 
mounting frame in a direction transverse to the direction of reciprocation 
of the reciprocable pump elements, as shown by double-headed arrow 16. 
Thus, the drive unit is reciprocable transversely in relation to the pump 
unit by sliding the drive unit along track 10. It will be obvious to those 
skilled in the art that the operation would remain unchanged if mounting 
plate 4 were stationary with respect to mounting plate 15 and thrust 
mechanism 1 were transversely reciprocable. 
The upper ends of the piston rods of the pumps are suspended on a 
respective one of levers 6 and 7 whereby reciprocation of thrust mechanism 
1 causes corresponding reciprocation of the suspended piston rods to drive 
the pumps. The illustrated suspension means is constituted by sliding 
element 17 mounted on guide column 14 for reciprocating sliding movement 
therealong. The sliding elements are connected to the levers in a manner 
to enable the levers to move transversely, with respect to the 
reciprocating direction thereof. This transverse movement in the direction 
of arrow 16 steplessly adjusts the stroke of each pump by changing the 
position of the fulcrum of each operating lever 6, 7, each fulcrum being 
constituted by a respective sliding element 17. Connecting part 3 of 
thrust mechanism 1 serves as a fixed point for the levers, the illustrated 
arrangement holding the levers laterally stationary with respect to the 
thrust mechanism by means of connecting part 3 while suspending means 17 
are held stationary with respect to the mounting frame for the pump unit, 
i.e., the pumps. 
When the pump and drive units are aligned with respect to center line 18 of 
the drive unit in the manner shown in FIGS. 2 and 3, the piston rod of 
pump 11 will have a shorter stroke than that of the piston rod of pump 12. 
Relative transverse movement between thrust mechanism 1 and piston rods 
suspended on the operating levers will steplessly change the ratios 
between the operating strokes of the two pumps which are driven in tandem 
by the pivoting levers. 
FIGS. 4 and 5 illustrate a specific suspension means 17 for the piston of 
the pump. In this embodiment, guide column 14 consists of two guide posts 
14, spaced apart in a direction perpendicular to the elongation of levers 
6, 7 and the suspension means 17 comprises a pair of guide plates 23 
interconnected by spacing member 22 and bushing 21 to form a sliding 
element guided along guide posts 14. The piston rod of the metering pump 
(not shown) is threadedly mounted in bushing 21 and extends downwardly 
therefrom between the guide posts. 
Socket 19 is held between spacing member 22 and bushing 21 to form part of 
the sliding element, and ball 20 is mounted for universal movement in the 
socket. The ball of the ball-and-socket joint has a diametrically 
extending bore which glidably receives lever 6, thus enabling the lever to 
slide therein in the direction of its longitudinal extension. Guide plates 
23 define openings 24 of a dimension sufficient to enable ball 20 to move 
universally, with lever 6. 
The piston rods of metering pumps 11, 12 are mounted so that, during their 
reciprocating stroke, fixed points define an accurately determined stroke. 
In the illustrated embodiment, levers 6 and 7 have a fixed point at 
connecting part 3 while they are transversely slidable in sliding elements 
17 and lateral supports 5 during reciprocation of the sliding elements for 
operation of the pumps. Other fixed points may be chosen for the operating 
levers, for instance by holding lever ends 8 fixed while the levers are 
slidable in sliding element 17 and connecting part 3, or holding the 
levers stationary in the sliding elements while they are slidable in 
supports 5 and connecting part 3. In all embodiments, the levers must be 
mounted stationary at one fixed point. 
The illustrate pump drive may be readily adapted to various space and other 
operating requirements. For instance, the metering pumps may be mounted 
above or below the thrust mechanism, or laterally thereof, i.e., the pump 
reciprocation may be effected in a horizontal direction and the movement 
of the thrust mechanism with respect to the pumps may then be vertical. 
In the embodiment illustrated in FIGS. 1 to 3, operating levers 6 and 7 are 
slidably mounted in sliding elements 17 and lateral supports 5 but, 
equivalently, instead of glidingly mounting lever ends 8 in supports 5, 
the lever ends may be slidably mounted in connecting part 3. Similarly and 
equivalently, sliding elements 17 sliding along guide columns 14 may be 
replaced by push rods suspending the reciprocable pump elements, for 
instance the piston rods, on the levers for transmitting the thrust of the 
pivoting levers to the reciprocable pump elements. Also, outer ends 8 of 
the operating levers may be held against reciprocation by push rods, 
straps or the like. Similarly, the thrust of mechanism 1 may be 
transmitted to levers 6 and 7 by means of push rods, straps or the like.