Metering pump

An arrangement for the volume-controlled feed of a medium, e.g. a liquid, in an outer flow system, comprising a movable pump piston (10) and a metering chamber (20) in connection, or connectable, to the flow system via a valve-controlled inlet (22) and outlet (23) for the intake and discharge respectively of the medium in time with the working cycles of the pump piston (10). To make possible the change between different desired feed volumes of the medium the arrangement has a wall element (15) delimiting the volume of the metering chamber (20) which is movable inside the metering chamber (20) for the adjustment of the desired metering chamber volume.

FIELD OF THE INVENTION 
The invention relates to metering pumps and more particularly to a metering 
pump for the flow-controlled feed of a medium from a source to a place of 
application of any kind in a flow system for the medium. 
BACKGROUND OF THE INVENTION 
Arrangements or metering pumps of the type described above have been known 
for a long time back and are used frequently in situations where media are 
to be conveyed in defined doses or flow rates for one purpose or another. 
This may refer to liquids, e.g. reagent solutions in connection with a 
chemical analysis process or a larger-scale industrial process which 
requires continuous supply of starting material at a correctly weighed out 
flow rate in order to achieve the optimum quality characteristics of a 
desired product, but situations also occur where gases or outright solid 
materials in finely divided fluid form are to be fed in volume-controlled 
portions according to some required working scheme. 
As indicated already the field of application for the known metering pumps 
is highly diversified both with regard to the types of media which are to 
be metered and the required size of the feed doses and flow rates 
respectively. The respective types of application have in common, though, 
that the metering pump used should fulfil at least a certain degree of 
accuracy of performance, so that the quantity of the particular medium 
actually fed corresponds as closely as possible to the quantity desired on 
the occasion. It happens frequently, though, that it is desirable, or 
necessary, to adapt the quantity of feed to a varying consumption 
requirement, so that, for example, during a certain period a large 
quantity of the medium has to be fed, whilst during a subsequent period a 
smaller quantity may be sufficient. To make possible such an adjustment or 
change-over between different desired doses or flow rates in a flexible 
manner, it is necessary consequently for the metering pump used to possess 
a corresponding flexibility of capacity. On certain known metering pumps 
of the type described with movable pump piston such a facility to change 
over between different desired metering volumes or flow rates has been 
made possible in that the driving arrangement or the motor which is used 
for driving the pump piston has been provided with some type of 
controllable power transmission arrangement to allow increase or decrease 
of the stroke frequency of the pump piston, as required. This type of 
variable metering pumps or, more precisely, this arrangement controlling 
the transmission, which is required in order to drive the pump piston at 
the desired rates, for obvious reasons, is greatly subject to wear and 
requires frequently recurring inspection and maintenance, especially if 
the metering pump is to be used in contexts demanding frequent changes 
between different metering volumes and which consequently put particularly 
severe loads on sensitive driving components for the pump piston. 
Known adustable metering pumps of a type somewhat more reliable in 
operation and simpler are those which operate at one and the same stroke 
frequency of the pump piston for the different metering volumes desired 
and which therefore do not require any supplementary, sensitive driving 
equipment of the type described just now. In the latter type of known 
metering pumps the desired variations in metering volumes are achieved 
instead with the help of stop elements limiting the stroke length of the 
pump piston which may be arranged either stepwise or freely movable in the 
pump cylinder or metering chamber. Metering pumps of this type certainly 
have a simpler and therefore more easily maneuverable design than the 
metering pumps with changing of the stroke frequency described above, but 
they present, on the other hand a somewhat less reliable accuracy of 
performance owing, among other things, to the elements, set for a desired 
metering volume, being very much subject to the risk of unintended shift 
of their set position as a result of the pump piston repeatedly striking 
against them. This risk naturally can be particularly serious where 
metering pumps are intended to be used for the metering of very small 
metering volumes required, since each smallest displacement of the element 
in such a case may give rise to substantial fault deviations from the 
metering volume desired. 
Against this background there is an apparent demand for a metering pump 
which is simple in its design and maneuverability and which requires 
little maintenance and which nevertheless allows flexible shifting between 
different metering volumes desired whilst retaining accuracy of 
performance, also during prolonged usage. 
OBJECTS AND SUMMARY OF THE INVENTION 
This demand has been met in accordance with the present invention through a 
metering pump which comprises a movable, preferably reciprocating pump 
piston and a metering or measuring chamber with valve-controlled inlet and 
outlet for the intake and discharge respectively of the medium which is to 
be metered in time with the corresponding working cycles of the pump 
piston.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 thus presents an arrangement or metering pump 1 in accordance with 
the present invention for the volume-controlled feed of a medium, e.g. 
liquid, into an outer flow system for the medium. The metering pump 1 
comprises an elongated cylindrical casing body 2 with side walls 3 and 4 
and end walls 5 and 6 which jointly enclose an inner cylinder chamber 
which with the help of a partition 7 is divided into a pump chamber 8 and 
a driving chamber 9. In the pump chamber 8 a pump piston 10 is supported, 
e.g. in a guide bearing 11, for an axially reciprocating movement between 
a front end position and a rear one indicated by broken lines. The pump 
piston 10 is driven with the help of a motor 12 and a driving shaft 13 
supported in displaceable manner in the rear end wall 5. 
As is evident from FIG. 1, the pump chamber 8 comprises a front space 14 of 
cylindrical shape of a somewhat smaller diameter than the rest of the pump 
chamber so as to form a seat for a cylindrical body 15 which is 
displaceable in the direction of movement of the pump piston 10 in the 
pump chamber 8 as will be explained. The cylindrical body 15 is arranged 
at one end of a guide rod 16 supported in displaceable manner in the 
driving chamber 9 by the partition 7 and the front end wall 6. Around the 
guide rode 16 in the driving chamber 9 is provided a slidable sealing 
plate 17, which is sealed off against the inside walls of the driving 
chamber 9 and which divides the driving chamber 9 into a rear expansion 
chamber 9' and a front spring chamber 9". A spring element 18 with seats 
against the front end wall 6 and the sealing plate 17 is arranged around 
the guide rod 16 in the spring chamber 9" for pressing the cylindrical 
body 15, rigidly connected to the sealing plate 17 via the guide rod 16, 
in the direction against the pump piston 10 in the pump chamber 8. The 
expansion chamber 9' is capable of communicating with a source (not shown) 
of pressure medium, e.g. air, via an inlet duct 19 provided in the side 
wall 4 of the casing body 2 to make possible the displacement of the 
cylindrical body 15 against the effect of the force of pressure of the 
spring element 18 against the sealing plate 17. A volume of the metering 
chamber 20 determining the metered medium between the cylindrical body 15 
and a front surface 21 of the pump piston 10 can communicate with the 
outer flow system for the medium via a valve-controlled (e.g. a check 
valve of the ball-type) inlet 22 and outlet 23 so as to make possible a 
metered flow of the medium in time with the pumping cycles of the pump 
piston 10. To prevent any leakage from the metering chamber 20, gaskets 24 
and 25 are provided in the cylindrical space 14 between the cylindrical 
body 15 and the inside wall of this space, and in the pump chamber 8 
between the pump piston 10 and inside wall of the chamber 8 respectively. 
When the arrangement shown in FIG. 1 is to be used for the feed at a 
maximum flow rate of, for example, a liquid into the flow system, the 
cylindrical body 15 is shifted to its most retracted position in the space 
14, so as to obtain the greatest possible volume of the metering chamber 
20 between the cylindrical body 15 and the front surface 21 of the pump 
piston in its rear end position (as shown by broken lines in FIG. 1). This 
means, therefore, that the pressure of the medium which flows into the 
expansion chamber 9' from the pressure source (not shown) via the 
connection duct 19 must be at least equal to, preferably greater than, the 
spring pressure from the element 18, so as to retain the sealing plate and 
the cylindrical body 15, rigidly connected therewith via the guide rod 16, 
in the position shown in FIG. 1. With the cylindrical body 15 in this 
position the metering pump 1 operates in principle, in the same manner as 
the similar, known arrangements of piston type, that is to say, during the 
intake stroke or movement backwards into the pump chamber 8 of the pump 
piston 10 with the help of the motor 12 and the driving shaft 13 the 
outlet 23 is shut whilst the inlet 22 is opened for the inflow of liquid 
into the metering chamber 20 until the pump piston has reached its rear 
end position. When the pump piston thereafter turns and is driven 
forwards, the inlet 22 is shut whilst the outlet 23 is opened for the 
discharge of the liquid from the metering chamber 20. 
When the metering pump in FIG. 1 on a later occasion is to be used for the 
feed of, for example, a minimum flow rate of the liquid, a procedure is 
adopted which is made evident best from FIG. 2. For the sake of greater 
clarity the same reference designations have been used in both figures for 
identical components. This means, therefore, that the pressure in the 
expansion chamber 9' is lowered through outflow of pressure medium from 
the chamber 9 until the pressure in this chamber is lower than the contact 
pressure of the spring element 18 against the sealing plate 17. As a 
result the sealing plate 17 will be shifted backwards (to the right in 
FIG. 2) so as to press the cylindrical body 15, rigidly connected 
therewith via the guide rod 16, against the front surface 21 of the pump 
piston 10, as shown by the fully drawn lines in FIG. 2. Thus the 
cylindrical body 15, resting against this surface 21 on the pump piston 
10, will follow the reciprocating working cycles of the pump piston in the 
pump chamber, when the motor 12 is started. In other words, the 
cylindrical body 15 and the pump piston 10 will move as a unit in the 
direction with the spring force from the element 18 during the intake 
movement of the pump piston 10 (towards the right to the end position 
shown in FIG. 2), whilst the same unit is displaced against this force 
during the pumping movement of the piston towards the left to the end 
position indicated by broken lines. The volume of liquid which in this 
manner will be sucked into the metering chamber 20 through the 
valve-controlled inlet 22, when the pump piston 10 together with the 
cylindrical body 15 move towards the rear end position and which 
thereafter will be discharged via the valve-controlled outlet 23, when in 
corresponding manner the pump piston 10 and the cylindrical body 15 move 
towards the left end position, corresponds to the maximum volume 
discharged in accordance with FIG. 1 minus the volume of the maximum part 
of the cylindrical body 15 introduced into the metering chamber 20 (FIG. 
2). 
While this invention has been illustrated and described in accordance with 
a preferred embodiment, it is recognized that variations and changes may 
be made therein without departing from the invention as set forth in the 
claims.