WO1981003222A1

WO1981003222A1 - Method and apparatus for dosing liquid

Info

Publication number: WO1981003222A1
Application number: PCT/DK1981/000047
Authority: WO
Inventors: T Christensen
Original assignee: Proteinkemisk Inst Tilknyttet; T Christensen
Priority date: 1980-05-01
Filing date: 1981-05-01
Publication date: 1981-11-12
Also published as: DK194680A; EP0050664A1

Abstract

By dosing liquid which is supplied to a dosing container (4) from a liquid reservoir through a liquid supply duct (5), the interior of the dosing container communicating at a first level with a liquid discharge duct (8) extending upwardly from said level, the liquid supply to the dosing container is interrupted when liquid is detected (10) at a second level above said first level in the dosing container or discharge duct. Thereafter, liquid is discharged from the dosing container through the discharge duct to said first level. An apparatus for dosing liquid comprises a dosing container (4) provided with a liquid supply duct (5), the interior of the dosing container communicating with an upwardly extending liquid discharge duct (8). A liquid detector (10) is arranged in a upwardly extending tubular part (9) of the dosing container (4), the liquid detector being adapted to control the liquid supply through the liquid supply duct. The dosing container (4) has a peripheral part (3) which is constructed as a stopper adapted to seal a flask containing the liquid which is to be dosed, and an axially extending pressure gas supply duct (2) is arranged in the stopper-shaped part. A non-return valve (6) is arranged in the lower part of the liquid supply duct (5), the lower part being adapted to be immersed into the liquid in the flask, and the non-return valve is adapted to prevent liquid from escaping from the dosing container through the supply duct.

Description

METHOD AND APPARATUS FOR DOSING LIQUID .

The present invention relates to a method for dosing liquid which is supplied from a liquid reservoir through a liquid supply duct to a dosing container, the interior of which is connected, at a first level, to a liquid discharge duct extending upwardly from said level, the supply of liquid to the dosing container being interrupted when liquid is detected, at a second level above said first level, in the dosing container or discharge duct, whereafter liquid is discharged from the dosing container through the discharge duct to said first level.

In many different situations , for example when dosing reagents in synthesis or analysis processes , including gauging and dosing derivatives etc in oligonucleotide synthesis and peptide synthesis , it is desired to gauge and dose an exact volume of liquid, especially a small volume, and to transfer it from a liquid container to another container or reactor. Different kinds of apparatuses for dosing liquid are known as well as different reaction systems , in which different kinds or types of apparatuses are employed for dosing the liquid. Generally, a gauging pump is used which is connected to the said other container or reactor through a single conduit, and which is connected, through a number of selector valves, to several liquid containers which contain the liquids to be transferred in turn to said other container. In a system of this type, there is a pronounced risk of mutual contamination of the liquid volumes gauged and transferred in the system owing to the selector valves and the common gauging pump . Futhermore, the system has the disadvantage that it may "spill" since the valves are not completely closely fitting and since, by the dosing, no complete emptying of the conduit connections takes place .

Reaction systems are also known in which the siphon principle is employed . U . S . patent No . 3, 557,077 discloses a system in which several liquid containers are connected to a common gauging container through individual conduit connections immersed in the liquid present in the container in question . Each of the liquid containers is connected to both a pressure source and an air-escape conduit through a three-way valve . Analogously, the gauging container is also connected to both said pressure source and said air-escape conduit through a three-way valve and connected to a reaction container through a solenoide valve or a siphon connection . When pressure is supplied to one of the liquid containers , liquid is pressed from the said container up into the gauging container wherein one liquid detector, arranged at a predetermined level, registers when a liquid volume corresponding to the said level has been transferred from the liquid container to the gauging container whereafter the supply of pressure to the liquid container in question is interrupted. Although the elimination of the selector valves employed in the first-mentioned system with associated gauging pump results in an improvement of the mode of operation of the system, the system is , nevertheless , not quite satisfactory . The fact is that the use of the common gauging container implies that the conduit connections between the individual liquid containers , which may have been placed at different levels , and the gauging container are of different lengths and sometimes excessively long. This , in combination with the difference in the elevational arrangement of the liquid containers , causes the pressures generated in the individual liquid containers by the above-mentioned pressure source to be equallized at different rates, depending on the liquid level, so that the liquid transfer becomes different from one container to another and furthermore becomes dependent on the density of the liquid present in the container in question . Accordingly, it will be seen that a liquid dosing will not be obtainable by means of a system of this kind having a sufficiently high accuracy. Furthermore, experience has shown that it is not possible to gauge liquid volumes of less than approximately 10 ml.

The present invention provides a method of the above-mentioned kind which renders possible an extremely accurate and density-in-dependent dosing of liquid volumes of less than 1 ml.

The method according to the invention is characteristic in that the inlet end of the liquid supply duct is arranged below the liquid level in the reservoir, and that the liquid is introduced into the dosing container by introduction of pressure gas into the reservoir. It is preferred that the liquid is discharged from the dosing container by introduction of pressure gas into it.

The invention also relates to an apparatus for use in carrying out the method described above and comprising a dosing container provided with a liquid supply duct, the interior of the dosing container communicating at a first level with a liquid discharge duct extending upwardly from said level, a liquid detector being arranged in the dosing container or discharge duct at a second level above said first level and adapted to control the liquid supply through the liquid supply duct so that the liquid supply is interrupted when the liquid detector detects liquid at said second level, and the apparatus according to the invention is characteristic in that the liquid detector is arranged in an upwardly extending tubular part of the dosing container, and that the tubular part is adapted to be connected to a pressure gas source . By arranging the liquid detector in an upwardly extending tubular part of the dosing container it is achieved that the relative change of the liquid level for a given increase in liquid volume becomes great, and thus, the accuracy of the liquid level detection is increased.

In a first embodiment of the invention the liquid supply duct is arranged in the lower end of the dosing container, the lower end being adapted to be immersed into the liquid which is to be dosed, a non-return valve, being arranged in the container or in the liquid supply duct, is adapted to prevent liquid from escaping from the container through the supply duct.

In a second embodiment of the invention the liquid supply duct is arranged in the lower end of the dosing container, the lower end being adapted to be immersed into the liquid which is to be dosed, and is in the form of a tube which extends upwardly to a certain level in the dosing container. It is preferred that a valve is arranged in the liquid supply duct in order to prevent accumulation of overpressure in the liquid reservoir when discharging the liquid from the dosing container.

The dosing container is especially advantageously constructed with a peripheral part which is formed as a stopper adapted to seal a hquid reservoir which contains the liquid to be dosed, an axially extending pressure gas supply duct being arranged in the stopper-shaped part.

The invention will be further described with reference to the drawing on which

Fig. 1 shows an embodiment of the invention formed as an insert member for mounting in a flask, a container or the like,

Fig. 2 and Fig. 3 a second embodiment of the invention in which the siphon principle is used, Fig. 4 a third embodiment of the invention formed, like the embodiment shown in Fig. 1 , as an insert member for mounting in a flask, a container or the like,

Fig. 5 a fourth embodiment of the invention, and

Fig. 6 a reaction system in which the insert member shown in Fig. 1 is used.

Fig. .1 shows an embodiment of the invention constructed as an insert member for mounting in an associated opening or an associated hole in a flask, a container or the like. The insert member, which may be made of glass , teflon, polyethylene or other appropriate material, comprises two parts 1 and 4, respectively, the part 4 being designated a gauging chamber. The part 1 which encircles the part 4 or the gauging chamber 4 is constructed having a cone 3 at the bottom which cone is adapted to fit in with an associated ground. joint in the associated flask or container.

Furthermore, the part 1 comprises an inlet tube 2 for supplying pressure to the associated flask or container. The gauging chamber 4, encircled by the part 1, is connected to the part 1 at the top thereof through an assembling 12. The lower end of the gauging chamber 4 extends into a cylindrical end piece 5 which is provided with a cylindrical passage. As will be understood, the part 4 and thereby the end piece 5 will submerge a distance into the flask or container when the insert member is mounted on the associated flask or container, and the end piece 5 may furthermore be equipped with a tubing which may suitably be so long that the end of the tubing reaches the bottom of the flask or container. Within the gauging chamber 4 a valve is arranged which is placed opposite to the end of the upper end of the end piece 5, together designated 6. The valve 6 comprises a precision-ground block-shaped body 6b which may be made of glass or another appropriate material and which is formed so that, when only the gravitation force acts on it, it abuts with a close fit an associated valve seat 6a which is provided in the upper end of the end piece 5 and which may also be produced by precision - grinding. The upper end of the gauging chamber 4 is provided with an external thread for liquid- and gas-tight connection with a corresponding thread adaptor 13 and associated gasket 14. The thread adaptor 13 and the gasket 14 are provided with through-going passages in which two riser pipes 8 and 9 are mounted so as to be gas-tight. The riser pipe 9 is provided with a liquid detector 10 which , in a manner known per se, generates a control signal when it detects liquid. The riser pipes 8 and 9 extend through the thread adaptor 13 and the gasket 14 and down into the gauging chamber 4, the lower end of the riser pipe 8 being arranged closer to the valve 6 than the lower end of the riser pipe 9.

In the following, the use of the insert member will be described assuming that the flask or container on which the insert member is mounted, only communicates with the environment through the pressure supply tube 2 of the insert member or through the central passage of the end piece 5, the valve 6 and the riser pipes 8 and 9, respectively, and that the end piece 5 of the insert member and associated tubing are immersed below the surface of the liquid in the container or the flask. A pressure source (not shown) is made to supply pressure to the container or the flask through the pressure supply tube 2. The pressure will cause the liquid in the flask or the container to rise into the end piece 5 of the insert member and associated tubing, and if the pressure is sufficiently high to overcome the gravity of the valve block 6b , the liquid will lift the latter and rise up into the interior of the gauging chamber 4 and further up into the riser pipes 8 and 9 , respectively . In the figure, the surface of the liquid 7 is shown in the gauging chamber 4 and designated 11. The lower end of the riser pipe 9 is placed at such a level that the volume of the quantity of air confined in the interior of the gauging chamber 4 by the rising liquid becomes as small as possible . If the riser pipe

9 is placed in direct extension of the gauging chamber 4, the confined air volume may be completely eliminated. Provided that the pressure supplied to the pressure supply tube 2 is sufficiently high, the liquid continues to rise in the riser pipes 8 and 9, respectively, until the liquid surface in the riser pipe 9 reaches the liquid detector 10. The control signal generated by the liquid detector 10 interrupts the pressure supply to the pressure supply tube 2 of the insert member 1, whereafter the weight of the liquid present in the interior of the gauging chamber 4 and associating riser pipes 8 and 9 instantaneously shuts the valve 6. Thereafter, the above-mentioned pressure source is reversed to supply pressure to the riser pipe 9, and this pressure forces liquid in the riser pipes 8 and 9, respectively, and in the gauging chamber 4 out through the riser pipe 8 until an "air short circuit" occurs between the riser pipes 8 and 9, which happens when the surface

11 in the gauging chamber 4 has reached the lower end of the riser pipe 8 and when the quantity of liquid present in the riser pipe 8 has been discharged. This "air short circuit" between the riser pipes 8 and 9 may suitably be detected by means of a liquid detector (not shown) which is mounted on the riser pipe 8 and which generates a control signal indicating the presence of said "air short circuit" between the riser pipes 8 and 9. As will be well- known to the skilled art worker, the liquid detectors mounted on the riser pipes 8. and 9 may be connected to a central control unit such as a mini- or microcomputer or a microprocessor which controls in succession the connection of the above-mentioned pressure source (not shown) to the pressure supply tube 2 of the insert member 1 and to the riser pipe 9.

As will be understood, the volume of the quantity of liquid transferred from the container and through the riser pipe 8 may be adjusted by adjusting the level of the riser pipe 8 in the gauging chamber 4.

In Figs . 2 and 3 , a second embodiment of the invention is shown in which the siphon principle is used. In order to facilitate the understanding, identical reference numerals are being used in

Figs . 2 and 3 for corresponding parts . In Fig. 2, a flask 21 is shown which is supplied with a liquid through the opening designated by an arrow. The surface of the liquid 22 supplied to the flask is in the Figure designated 23. In the flask, a siphon 24 is arranged, on the outlet branch of which a liquid detector 25 is mounted. The inlet end 26 of the siphon is immersed to a first level in the liquid 22 present in the flask to a first level, and the arrangement of said siphon in the flask defines a second level, at which the siphon starts discharging the liquid from the flask. By continuous supply of liquid to the flask, the liquid surface 23 will rise to said second level, whereby the liquid detector mounted in the outlet branch of the siphon detects liquid and in a manner known per se interrupts the supply of liquid to the flask. Thereafter, the siphon continues to discharge liquid to said first level, whereupon the liquid detector again generates a signal corresponding to the change. As will be understood, the apparatus having only a single liquid detector provides an extremely simple, but at the same time extraordinarily exact liquid dosing.

In Fig. 3, the dosing apparatus shown in Fig. 2 has been connected to a liquid container 27 supplying liquid. The flask 27 comprises two orifices , one of which is equipped with a stopper 28 , through which a siphon 29 is immersed in the liquid 30 present in the flask 27. The other orifice of the flask, which is designated by an arrow, is adapted to be connected to a pressure source in a manner known per se so that supply of pressure through this orifice transfers liquid from the flask 27 and into the flask 21 and so that the pressure supply and thereby the liquid supply are controlled by said liquid detector 25. Although only a single liquid container is shown in Fig. 3, it will be appreciated that several liquid containers may be used and that the liquid transfer in succession from the liquid containers may be controlled by said liquid detector 25 and a central control unit as already mentioned in connection with Fig. 1.

Fig. 4 shows a third embodiment of the invention, which is in the form of an insert member like the embodiment shown in Fig. 1, for mounting in an associated opening or an associated hole in a flask, a container, or the like . In order to facilicate the understanding, reference numerals identical to those in Fig. 1 are being used in Fig. 4 for identical parts . The embodiment of the invention shown in Fig. 4 differs from the embodiment shown in Fig. 1 primarily by elimination of the valve 6 shown in Fig. 1. Instead, a riser pipe 31 is mounted through the lower part of the gauging chamber 4 and extends to a level in the interior of the gauging chamber, the level being designated 32. Furthermore, in Fig. 4, a level 33 is indicated, which is defined by the lower end of the riser pipe 8.

As will be appreciated, the use of the insert member shown in Fig. 4 does not differ significantly from the use of the insert member shown in Fig. 1. Thus , liquid is transferred to the gauging chamber 4 in the insert member shown in Fig. 4 by supplying pressure to the pressure supply tube 2. This pressure causes the liquid in the flask or container, in which the insert member is mounted, to rise in the interior of the gauging chamber 4 until the liquid detector 10 mounted on the riser pipe 9 detects liquid . The liquid detector 10 interrupts the supply of pressure to the pressure supply 2 by way of the previously mentioned, central control unit (not shown) , and thereby the surface of the liquid present in the interior of the gauging chamber 4 drops to the level 32 previously mentioned, which is defined by the upper end of the riser pipe 31. Thereafter, as explained above in connection with Fig. 1, the pressure source is reversed to supply pressure to the riser pipe 9 whereby a liquid transfer takes place .

In contrast to the insert member shown in Fig. 1 , the volume of the quantity of liquid transferred from the container and through the riser pipe 8 is defined by both the level of the riser pipe 8

(the level 33) and the level of the riser pipe 31 (the level 32) in the gauging chamber 4. In Fig. 5, a fourth embodiment of the invention is shown, which is basically a combination of the embodiments of the invention shown in Figs . 3 and 4. Thus , in Fig. 5 reference numerals identical to those in Fig. 3 are used for corresponding parts . The flask 27 which contains the liquid 30 to be gauged and dosed, is supplied with pressure as in Fig. 3 into an orifice which is designated by an arrow. A tube 34 is mounted in the stopper 28 which is mounted in one of the orifices of the flask 27, and a two-way valve 35 is inserted in the tube 34 which may be a manually controlled valve or a solenoide valve. The pipe 34 extends from the liquid 30 in the flask 27 and through the solenoide valve 35 up into a container 36, which corresponds to the gauging chamber 4 in the embodiment shown in Fig. 4, to a level which is designated 42 in the figure and corresponds to the level 32 in Fig. 4. In the container 36, a riser pipe 38 is arranged which corresponds to the riser pipe 8 in Fig. 4 and which defines a level 43 in the container 36 as the riser pipe 8 in Fig. 4 defines the level 33. Furthermore, the embodiment of the invention shown in Fig. 5 comprises a riser pipe 39 corresponding to the riser pipe 9 shown in Figs . 1 and 4 in which a liquid detector 40 is mounted, which corresponds to the liquid detector 10 shown in Figs . 1 and 4. The riser pipes 38 and 39 are mounted in the container 36 in a stopper 41.

As will be appreciated, the use of the embodiment of the invention shown in Fig. 5 is completely analogous to the use of the embodiments of the invention shown in Figs . 2 - 4. Thus , if the two-way valve 35 is opened, liquid is transferred from the flask 27 and into the container 36 by supply of pressure to the orifice of the flask 27 which is designated by an arrow. Like the liquid detector 10 in the embodiments of the invention shown in Figs . 1 and 4, the liquid detector 40 is adapted to interrupt the supply of pressure to the flask 27 so as to interrupt the transfer of liquid from the flask and to the container 36. After interruption of the pressure supply, the surface of the liquid present in the container 36 drops to the level 42 within a relatively short period of time, whereupon the two-way valve 35 is closed in order to prevent accumulation of overpressure in the container 36 as the riser pipe 39 is supplied with pressure for transfer of liquid from the container 36 through the riser pipe 38. As will be appreciated, the volume of the quantity of liquid gauged in the container 36 and the quantity of liquid transferred from the container are determined by the levels 42 and 43, a residual volume 37 being present after transfer of liquid from the container 36.

In Fig. 6 a reaction system is shown in which the insert member shown in Fig. 1 is employed. The reaction system which is adapted to peptide or oligonucleotide synthesis is divided into two halves , a "dry" (non-aqueous) and an aqueous system, respectively, shown in the left half of Fig. 6 and the right half of Fig. 6, respectively. Odd indices in reference numerals refer to the "dry" half of the reaction system, and even indices in the reference numerals refer to the aqueous half of the reaction system, whereas reference numerals without indices refer to components of the reaction system common to the two said halves . A pressure source TK is connected through a dryer to a pressure pipe T common to the two halves of the reaction system, the "dry" system and the aqueous system, respectively . In the following, the "dry" system will be described first. The system is connected to said pressure pipe T through a two-way valve A ₁ and two three-way valves B₁ and B₃ , respectively, which may be reversed for venting through venting pipes V₁ and V₃, respectively, and associated dryers . The two-way valve A₁ is connected to two pressure pipes L₁ and L₃, respectively, through two manually controlled two-way valves C₁ and G₁, respectively, which may, alternatively, be constructed as solenoide valves, the pressure pipes L₁ and L₃ further being connected to each of the three-way valves B ₁ and B₃ , respectively. A number of flasks S₁, S₃, S₅ , S₇, S₉ and S₁₁, in which insert members corresponding to the insert member 1 shown in

Fig. 1 are mounted, are through riser pipes corresponding to the riser pipe 9 in the insert member shown in Fig. 1 and including individual liquid detectors D ₁, D₃, D₅, D₇, D₉ and D₁₁ , respectively, corresponding to the detector 10 in Fig. 1 , and through associated two-way valves F₁ , F₃, F₅, F₇ , F₉ and F₁₁ connected to said pressure pipe L₁ . The pressure pipe L₃ is through associated two-way valves E₁ , E₃ , E₅, E₇ , E₉ and E ₁₁ , respectively, connected to pressure supply pipes , corresponding to the pipe 2 in the insert member shown in Fig. 1 , in the insert members mounted in the flasks S₁, S₃, S₅, S₇, S₉ and S ₁₁. Riser pipes corresponding to the riser pipe 8 in Fig. 1 are from each of the flasks connected to a common manifold M₁ , the outlet orifice of which is connected to a two-way valve N₁.

The aqueous half of the reaction system is constructed analogously to the "dry" system. The aqueous system is through a two-way valve A₂, a three-way valve B ₂, and a three-way valve B ₄ corresponding to the valves A₁ , B₁ , and B₃, respectively, of the "dry" system, connected to said pressure pipe T . The aqueous half of the reaction system includes two two-way valves C₂ and G₂, corresponding to the two-way valves C₁ and G₁ , respectively, of the "dry" system, which analogously to the "dry" system are connected to said two-way ^"valve A₂ and two pressure pipes L₂ and

L₄, respectively, which are in turn connected to the three-way valves B₂ and B₄ , respectively. Venting pipes V ₂ and V₄ are connected to the three-way valves B ₂ and B₄, respectively, but, in contrast to the pipes V₁ and V₃ in the "dry" system, they do not necessarily include dryers . Analogously to the flasks S ₁ , S₃,

S₅, S₇, S₉ and S₁₁ in the "dry" system, the aqueous system includes flasks S₂, S₄, S₆, S₈, S₁₀ and S₁₂ in which insert members corresponding to the insert member shown in Fig. 1 are mounted. Riser pipes, corresponding to the riser pipe 9 in Fig. 1 , in the insert members in the flasks S₂, S₄, S₆, S₈, S_{1 0} and S₁₂ are through liquid detectors D₂, D₄, D₆, D₈, D₁₀ and D₁₂, respectively, and associated two-way valves F₂, F₄, F₆, F₈, F₁₀ and F₁₂, respectively, connected to said pressure pipe L₂. The pressure pipe L₄ is through two-way valves E₂, E₄, E₆, E₈, E₁₀ and E₁₂ connected to pressure supply pipes, corresponding to the pipe 2 in Fig. 1, in corresponding insert members in the flasks S₂ - S ₁₂ in the aqueous system . Corresponding to the manifold M₁ of the "dry" system, a manifold M₂ is connected to riser pipes , corresponding to the riser pipe 8 in Fig. 1 , in the flask insert members of the aqueous system . The manifold M₂ is , through a two-way valve B₆ connected to a two-way valve N₂ corresponding to the two-way valve N.. in the "dry" system. The two-way valves N ₁ and N₂ are jointly connected to a pipe in which both a liquid detector Y and a two-way valve I are mounted. The two-way valve I is in turn connected to both a reactor R and an outlet pipe in which a two-way valve J and a liquid detector X are mounted. Furthermore, the reactor R is connected to said pressure pipe T through a two-way valve A and a three-way valve B , which may be reversed for venting through a venting pipe V provided with a dryer. All of the above-mentioned liquid detectors and two-way and three-way valves are connected to a central control device (not shown) as already mentioned in connection with the description of Figs . 1, 2, and 3, e.g. a mini- or microcomputer or the like.

The mode of operation of the reaction system will now be explained. As wiH be appreciated, the flasks S₁ - S ₁₁ of the "dry" system contain liquids which must not come into contact with the water contained in the atmosphere whereas the flasks S ₂ - S_{1 2} of the aqueous system contain liquids which are not damaged by contact with the water contained in the atmosphere . The liquid dosing which has already been described, in principle, in connection with Fig. 1 is established in the following manner, the "dry" system being considered exclusively. At first, all of the two-way valves F₁ - F ₁₁, E₁ - E ₁₁, A₁ , C₁ , and G₁ are closed, and the three-way valves B₁ and B ₃ are in their venting positions . Thereafter, both of the two-way valves associated to a flask, e .g. F ₁ and E₁ associated to the flask S ₁ , are opened, and simultaneously, the three-way valve B₃ is reversed for connection to the pressure pipe T . Thereby, liquid is pressed up into the insert member mounted in the flask S₁ until the liquid detector D ₁ detects liquid, whereupon the three-way valve B₃ is reversed to the venting position, and the two-way valve E ₁ is closed . The discharge of the liquid present in the dosing chamber through the riser pipe, corresponding to the riser pipe 8 in Fig. 1 , is performed by reversing the three-way valve B ₁ for connection of the riser pipe, corresponding to the riser pipe 9 in Fig. 1, to the pressure pipe T through the two-way valve F₁ . Thereby, the liquid present in the dosing chamber is transferred to the manifoldM₁ . By repeating the dosing cycle just described, liquid may be transferred from another one of the flasks S₃ - S ₁₁ to the manifold M₁. The liquid present in the manifold M₁ is further transferred to the reactor R by opening the two-way valves N₁ and I, the above-mentioned control device (not shown) controlling the transfer of liquid by means of the liquid detector Y which generates control signals both when it detects liquid and when it ceases to detect liquid. During the liquid transfer, the reactor is vented through the three-way valve B and the venting pipe V and associated dryer. Thereafter, the three-way valve B is reversed and the valves F₁ , B ₁, N_1. and I are closed, and then the reactor is activated for a certain period of time in order to obtain the desired effect. The reactor is emptied through the above-mentioned outlet pipe by opening the two-way valves A and J, causing the liquid present in the reactor to be pressed out through the outlet pipe, the emptying being controlled as described above in connection with the liquid detector Y by the above-mentioned control device (not shown) by means of the liquid detector X.

The aqueous half of the reaction system functions in a manner completely analogous to the manner just described with one single exception. As already mentioned, a two-way valve B₆ is inserted in connection between the manifold M₂ and the two-way valve N₂. Furthermore, the two-way valve N₂ is connected, through a two-way valve B₀, to the pipe connection to the riser pipe, corresponding to the riser pipe 8 in Fig. 1 , in the insert member mounted in the flask S₁ . Normally, the two-way valves B₀ and B₆ are closed and open, respectively, so that the "dry" and the aqueous systems function completely separately. However, the insertion of the two-way valves B₀ and B₆ and the connection from the flask S₁ to the two-way valve N₂ permit transfer of liquid from the flask S₁ to the two-way valve N₂ in order to rinse the latter. The special advantage of this is that it becomes possible to rinse the part of the aqueous system which comes into direct contact with the "dry" system, with the detergent of the "dry" system contained in the flask S ₁.

In certain cases , it may be advantageous to vent vapours from the pressure pipes L₁ , L₃, L ₂ and L₄, which is performed by opening the two-way valves A₁ and A₂, respectively, and passing an air current through the two-way valves C₁ and C₂, respectively, and G₁ and G₂ , respectively, and further through the three-way valves B ₁ and B₂ , respectively, and B₃ and B₄, respectively, for venting .

Although the reaction system shown in Fig. 4 includes a "dry" system and an aqueous system, each comprising six flasks , it should be understood that several modifications of the reaction system may be performed without deviating from the fundamental idea of the invention as more or less than 2 subsystems may be employed, each comprising an arbitrary number of flasks .

Claims

Claims .

1. A method for dosing liquid which is supplied from a liquid reservoir through a liquid supply duct (5, 31, 34) to a dosing container (4, 36), the interior of which being connected, at a first level (33, 43), to a liquid discharge duct (8, 38) extending upwardly from said level, the liquid supply to the dosing container being interrupted when liquid is detected (10, 40), at a second level above said first level, in the dosing container or discharge duct, whereafter liquid is discharged from the dosing container through the discharge duct to said first level, c h a r a c t e r i z e d in that the inlet end of the liquid supply duct is arranged below the liquid level in the reservoir, and that the liquid is supplied to' the dosing container by introducing pressure gas (2) into the reservoir.

2. A method according to claim 1, c h a r a c t e r i z e d in that the liquid is discharged from the dosing container by introducing pressure gas (9, 39).

3. An apparatus for use in carrying out the method according to claim 1 and comprising a dosing container (4, 36) provided with a liquid supply duct (5, 31, 34), the interior of the dosing container communicating, at a first level (33, 43), with a liquid discharge duct (8, 38), a liquid detector (10, 40) being arranged in the dosing container or discharge duct at a second level above said first level and adapted to control the liquid supply through the liquid supply duct so that the liquid supply is interrupted when the liquid detector detects liquid at said second level, c h a r a c t e r i z e d in that the liquid detector (10, 40) is arranged in an upwardly extending tubular part (9, 39) of the dosing container (4, 36), and that the tubular part is adapted to be connected to a pressure gas source.

4. An apparatus according to claim 3, c h a r a c t e r i z e d in that the liquid supply duct is arranged in the lower end (5) of the dosing container, the lower end being adapted to be immersed into the liquid which is to be dosed, and that a non-return valve (6), being arranged in the container or in the liquid supply duct, is adapted to prevent liquid from escaping from the container through the supply duct.

5. An apparatus according to claim 3 or 4, c h a r a c t e r i z e d in that the liquid supply duct (31, 34) is arranged in the lower end of the dosing container, the lower end being adapted to be immersed in the liquid which is to be dosed, and is in the form of a tube which extends upwardly to a certain level (32, 42) in the dosing container (8, 36).

6. An apparatus according to claim 5, c h a r a c t e r i z e d in that a valve (35) is arranged in the liquid supply duct, the valve being adapted to prevent accumulation of overpressure in the liquid reservoir by discharging the liquid from the dosing container.

7. An apparatus according to any one of claims 3 - 6, c h a r a c t e r i z e d in that the dosing container (4) has a peripheral part (3) which is formed as a stopper adapted to seal a liquid reservoir which contains the liquid to be dosed, and that an axially extending pressure gas supply duct (2) is arranged in the stopper-shaped part.