IE50187B1

IE50187B1 - Improvements in micropumps

Info

Publication number: IE50187B1
Application number: IE1752/80A
Authority: IE
Original assignee: Boehringer Sohn Ingelheim
Priority date: 1979-08-20
Filing date: 1980-08-19
Publication date: 1986-03-05
Also published as: NO155358B; DK356980A; AU544213B2; EP0024313B1; ZA805103B; EP0024313A1; ES8105829A1; ATE4290T1; FI67434C; DE2933617A1; ES494358A0; FI802588A; JPS5632082A; IL60854A0; IE801752L; DK147844C; DK147844B; CA1152379A; NO802439L; NZ194707A

Abstract

1. Process for metering small quantities of liquid without leaving a residue by means of a micro-piston pump having a capillary cylinder in which a piston, which fits in gastight manner therein, is mounted so as to be movable between a top dead centre and a bottom dead centre, the cylinder at its end located opposite the base of the piston opening into a twoway valve which connects the space in the cylinder alternately to an inlet and to an outlet (which connects the cylinder to the atmosphere during the first stage of the intake operation), characterised in that the piston and the valve are moved in such a way that, during the intake operation, first a defined quantity of air and then a defined quantity of liquid is transported into the cylinder, the quantity of air being such that, as the piston moves downwards to bottom dead centre, all the liquid is expelled through the outlet line.

Description

This invention relates to micropumps which may be used for the residue-free metering of very small quantities of liquid. Such pumps may be used, for example, for supplying a regulated quantity of medicinal substance to the atomiser plate of a piezoelectric atomiser. (See for example DE-OLS 2537755).

According to the invention there is provided a process for metering small quantities of liquid without leaving a residue by means of a micro-piston pump having a capillary cylinder in which a piston, which fits in gastight manner therein, is mounted so as to be movable between a top dead centre and a bottom dead centre, the cylinder at its end located opposite the base of the piston opening into a twoway valve which connects the space in the cylinder alternately to an inlet and to an outlet (which connects the cylinder to the atmosphere during the first stage of the intake operation), wherein the piston and the valve are moved in such a way that, during the intake operation, first a defined quantity of air and then a defined quantity of liquid is transported into the cylinder, the quantity of air being such that, as the piston moves downwards to bottom dead centre, all the liquid is expelled through the outlet line.

The valve is preferably a spool valve mounted in a block mounting the cylinder. In a preferred embodiment the cylinder chamber is of such a diameter that owing to capillarity the air column between piston head and liquid is maintained during changes of position of the pump.

In order that the invention may be readily understood, an embodiment thereof will now be described by way of example with reference to the accompanying drawings in which:Figure 1 is a vertical sectional view of a micropump in accordance with the invention; Figure 2 is a view similar to Figure 1 showing the pump at a later staje in its cycle of operation; and Figure 3 is a vertical part section taken along the line III-ΠΙ in Figure 1. 80187 The pump comprises a piston 1, preferably of highgrade steel, movably mounted in a very narrow capillary cylinder 2 which can be made for example of glass or metal. The cylinder 2 terminates in a valve block 4 made for example of plastics such as polytetrafluorethylene, in which the gas-tight closing valve spool 5, made preferably of high-grade steel, can be moved between the stops 6 or 7, as the case may be.

The position of the necked portion 8 of the valve slide 5 in relation to the inlet 9 and outlet 10 respectively results in a communication between the Inlet and outlet respectively and the chamber 11 of the cylinder.

The piston 1 is in its bottom dead centre position when the piston grip 12 abuts the cylinder, as shown in Fig. 1. The metered dose is determined by the product of the interior cross sectional area of the cylinder and the stroke between marks a and c.

The movement of the piston 1 and valve slide 5 is controlled so that the following cycle of action takes place: a) With the outlet opened (stop 7 lies against the valve block) the piston moves out of the position shown in Figure 1 in the direction A until a certain quantity of air is drawn into the cylinder (the end face of the piston is at mark a). The quantity of air is calculated, so that it expels all the liquid out of the valve and the outlet line when the micropump is emptied. b) In the second step, communication is made between the inlet 9 (and consequently the supply vessel) and the cylinder by displacing the valve slide in the direction D to the stop. c) The piston 1 is moved further in the direction A until the volume of liquid fixed by the stroke and cylinder cross section is drawn in (final position shown in Figure 2). The end face of the piston is at mark c. d) The valve slide 5 is returned in the direction C to the stop so that communication is made between the cylinder 2 and outlet 10. e) The piston 1 moves to the bottom dead centre (position shown in Figure 1). In so doing, first the liquid and then the air are driven out of the cylinder 2 and expelled through the outlet line. The air is used to blow free the valve and the outlet line. After this emptying operation the initial position is resumed.

The micro-pump according to the invention serves preferably for metering quantities of liquid in the range from 10 to 50 μΐ, but can also be designed for larger or smaller volumes by changing the dimensions. The use of a sufficiently narrow cylinder ensures that owing to the capillarity the air column between the piston and liquid is maintained even in the case of changes of position of the filled micro piston pump.

Mechanical or electrical means known per se serve to control the above-described cycle of action. However, operation of the pump can also be controlled by hand. A simple device for the purpose of control consists of a combination of gear wheels, racks and levers composed as follows: Four gear wheels are arranged next to one another and connected rigidly to one another. The periphery of the gear wheels is occupied only partly with teeth in such a way that substantially only one gear wheel becomes effective at a certain point in time. Thus, while, for example, the first gear wheel causes the action (a) via a rack and lever, the other three run freely until the desired quantity of air has entered the cylinder. The second gear wheel then ensures the adjustment of the valve slide, while the first gear wheel simultaneously moves the piston to the top dead centre position. Thence35 forward, the gear wheel brings the valve slide into the outlet position. The fourth gear wheel together with the associated transmission elements thereafter moves the piston to the bottom dead centre position. The control mechanism is such that after the gear wheels have turned through 360° all the elements are again situated in the initial position.

In another embodiment of the control device the turning movement is replaced by an up-and-down movement. For this purpose, it may be advantageous to arrange the cylinder and valve so that the directions of movement of the piston and valve slide run parallel.

Claims

1. Process for metering small quantities of liquid without leaving a residue by means of a micro-piston pump having a capillary cylinder in which a piston, which fits in gastight manner therein, 5 is mounted so as to be movable between a top dead centre and a bottom dead centre, the cylinder at its end located opposite the base of the piston opening into a twoway valve which connects the space in the cylinder alternately to an inlet and to an outlet (which connects the cylinder to the atmosphere during the first stage of the intake 10 operation), wherein the piston and the valve are moved in such a way that, during the intake operation, first a defined quantity of air and then a defined quantity of liquid is transported into the cylinder, the quantity of air being such that, as the piston moves downwards to bottom dead centre, all the liquid is expelled 15 through the outlet line.

2. Process for metering small quantities of liquid substantially as hereinbefore described with reference to the accompanying drawings.