METHOD AND APPARATUS FOR DOSING A FLUID

Abstract: The invention relates to a method and an apparatus for dispensing, during a short period of time, a predetermined volume of a fluid into a substantially constant flow of said fluid. The novel matter of the invention resides in that the fluid is introduced at a constant flow into a dosing apparatus and passes therethrough at the same flow in a first flow path. During a predetermined period of time, the throughflow of fluid is stopped by preventing the outflow from the dosing apparatus along the first flow path, whereby a desired fluid volume is dispensed in the dosing apparatus, and whereby the fluid leaves said dosing apparatus at a constant flow in a second flow path. During a short period of time, the dosed fluid volume is caused to flow from the dosing apparatus in the second flow path. From the dosing apparatus, the fluid is caused to flow at a constant flow along the first flow path, while preventing fluid from entering the dosing apparatus. To fill the dosing chamber of the dosing apparatus, fluid is introduced at a constant flow and flows through the dosing apparatus in said first flow path and leaves the dosing apparatus at a substantially constant flow.

Description: METHOD AND APPARATUS FOR DOSING A FLUID The present invention relates to a method and an apparatus for dispensing, during a short period of time, a predetermined volume of a fluid into a substantially constant flow of said fluid. More particularly, the invention relates to a method and an apparatus for producing a substantially constant flow of a carrier fluid for a second fluid or substance which, for example, is to be analysed in a chemical apparatus, the supply of said second fluid or substance being stopped intermittently by periodically dispensing a predetermined larger volume of said carrier fluid. In other applications of the invention, a diluent or a solvent may be substituted for the carrier fluid. The invention is also applicable to a control system in which a momentary and defined increase of the fluid flow is required for control purposes, such as in some fluidistor types. Furthermore, the invention is applicable to a control system for a centrifugal separator of the type that requires a substantially constant fluid flow for keeping it closed and a considerably larger fluid flow for opening and closing. There is already known an apparatus which gives a constant fluid flow and which, during a short period of time, dispenses a considerably larger volume of the fluid. The apparatus comprises a water supply line with branches to a water tank having a float-controlled supply valve and to a supply line having a solenoid valve. The water tank is mounted on a level set to give a con¬ stant flow through a conduit connected to the supply line. The solenoid valve is opened and closed by means of a timer for dispensing dosed water volumes into the constant water flow. However, the dosed volumes will not be sufficiently exact for applications where high precision is required, int. al . because of the pressure variations in the supply line and because of the time control as a result of the a.c. crossovers. Moreover, the reproducibility in respect of the flow characteristic is frequently unsatisfactory. It _is the o ject of this invention to provide a method and an apparatus for dispensing into a substantially constant fluid flow a highly exact and adjustably dosed fluid volume. Another object of the invention is to achieve rapid emptying of the dosed fluid volume. A further object is to provide a method and an apparatus for dispensing a dosed volume of high repro¬ ducibility. These objects are achieved, according to the in- vention, by a method which comprises introducing the fluid at a constant flow into a dosing apparatus and conducting it therethrough at the same flow in a first flow path; stopping the throughflow for a predetermined period of time by preventing the outflow from the dosing appa¬ ratus in said first flow path, whereby a desired fluid volume is dosed in said dosing apparatus, and whereby said fluid leaves said dosing apparatus at a constant flow in a second flow path; causing the dosed fluid volume to flow out of said dosing apparatus in said second flow path during a short period of time; causing fluid to flow out of said dosing apparatus at a constant flow along first flow path, while preventing dispensing of fluid into said dosing apparatus; and dispensing fluid at a constant flow into said dosing apparatus and conducting it therethrough in said first flow path, whereby the dosing chamber of said dosing apparatus is filled, and whereby the fluid flows out of said dosing apparatus at a substantially constant flow. ' . An apparatus for carrying the method into effect comprises, according to the invention, a body with a dosing chamber and a container for compressible medium, said dosing chamber and said container being separated by a partition having a bore, a piston arrangement having a first piston member in sliding and sealing engagement with said dosing chamber, and a second piston member in sliding and sealing engagement with a cylinder arrange¬ ment in the container, said piston members being inter¬ connected by means of a hollow piston rod mounted in the bore of the partition and having openings in said first piston member, and said first piston member having a cross-sectional area larger than that of said second piston member, a channel means formed in said partition and adapted to be connected, at one peripheral end, to a first conduit for constant flow fluid supply and, at its other peripheral end, to a second conduit communi¬ cating with the dosing chamber, a third piston member freely movable between said first piston member and said partition and in sliding and sealing engagement with both the dosing chamber and the piston rod, a first valve means for controlling the fluid flow in said second conduit, a second valve means for pressurised supply of a working medium to said piston arrangement, and a third conduit for the fluid flow from the dosing appa- ratus. Developments of the invention are defined in the subclaims. A preferred embodiment of the invention is described below, reference being had to the accompanying drawing in which Fig. 1 is a longitudinal section of an apparatus according to the invention for dispensing, during a short period of time, a predetermined volume of a fluid into a substantially constant flow of said fluid; Fig. 2a is a section similar to Fig. 1 but on a reduced scale, showing the apparatus according to the invention during dispensing; Fig. 2b is a section similar to Fig. 2a, showing the apparatus during emptying of the dispensed fluid volume; Fig. 2c is a section similar to Fig. 2a, showing the apparatus during emptying of the remaining active fluid volume in the dosing chamber of said apparatus; and Fig. 2d is a section similar to Fig. 2a, showing the apparatus during filling of the dosing chamber, i.e. when the apparatus is returning into its normal state as shown in Fig. 1. A preferred embodiment of the invention will now be described with reference to Fig. 1. The apparatus comprises a body 1 having a dosing chamber 2 and a ves- sel 3 for a compressible medium, such as compressed air. The dosing chamber 2 is separated from the vessel 3 by a partition 4 fixedly mounted in the body 1 and having a central bore 5 therethrough. A piston arrangement 6 is movably mounted within the body 1 and in the longi- tudinal direction thereof. Said piston arrangement com¬ prises a first piston member 7 in sliding and sealing engagement with the longitudinal inner wall of the dosing chamber 2, a second piston member 8 in sliding and sealing engagement with the longitudinal inner wall of a cylinder arrangement 9 within the vessel 3, and a piston rod 10 fixedly interconnecting said piston members 7 and 8 for simultaneous movement thereof. The piston rod 10 is in sliding and sealing engagement with the bore 5 of the partition 4. Furthermore, the piston rod is formed with a central bore 11 extending through said second piston member 8 and into, but not through, the first piston member 7 in which a plurality of openings 12 communicate said central bore 11 with the interior of the first piston member 7, which is open downwardly in the drawing. It should be noted that the first piston member 7 has a larger cross-sectional area than the second piston member 8 which, on its side facing the first piston member 7, carries a stop ring 13 of a cushioning material, such as rubber. The cylinder arrangement 9 is fixedly mounted in the container 3 and coaxially aligned with the piston rod 10 and, thus, also with the body 1. Adjacent the partition 4, the cylinder arrangement has a number of through holes 14 communicating the container 3 with the interior of the cylinder arrangement above the second piston member 8. The partition 4 is formed with channels 15 and 16 extending perpendicular to the longitudinal axis of the apparatus. The peripheral end of one channel 15 is adapted to be connected to a first conduit 17 for constant flow fluid supply, and the peripheral end of the other channel 16 to a second conduit 18 communi¬ cating with the upper part of the dosing chamber. The inner ends of the two channels 15 and 16 communicate, via passages 19, with the dosing chamber 2 underneath the first piston member 7. Between the first piston member 7 and the partition 4, a third piston member 20 is freely movable in sliding and sealing engagement with both the wall of the dosing chamber 12 and with the piston rod 10. The third piston member 20 has an annular groove 21 which is open towards the partition 4. The groove 21 is concentrically oriented relative to the longitudinal axis of the apparatus and faces the passages 19 in the partition. The first conduit ' 17 is provided with a flow meter 22 and has, between said flow meter 22 and the partition 4, a non-return valve or solenoid valve 23. The other conduit 18 for fluid flow from the partition 4 to the upper part of the dosing chamber 2 has, adjacent to the partition, a solenoid valve 24 and after that a non-return valve 25. A third conduit 26 for fluid flow away from the apparatus is provided in the upper part of the dosing chamber at a distance from the second conduit 18. The vessel 3 is supplied with compressed air through a fourth conduit 27 via a pressure reducing valve 28. Furthermore, the vessel 3 communicates with the piston arrangement 6 via a fifth conduit 29 in which a three-way solenoid valve 30 is mounted. The fifth conduit 29 extends from the vessel 3 to the cylinder arrangement 9 where it opens underneath the second piston member 8, permitting the compressed air to flow from the vessel, through the conduit, the bore 11 of the piston rod, the openings 12 to the space between the lower surface of the first piston member 7 and the upper surface of the third piston member 20 in the dosing chamber 2. The flow meter 22 and a timer (not shown) are connected to the solenoid valve 30 for operation thereof. Also the solenoid valve 24 is connected to the timer. The function of the apparatus will now be described with reference to Figs 2a-2d, as applied to a control system for a separator. In the normal state of the apparatus (Fig. 1), the third piston member 20 seats against the partition 4 and the first piston member 7 against the third piston member, on the one hand because of the water pressure within the dosing chamber, which acts upon the first piston member, and on the other hand because of the air pressure within the cylinder arrangement 9, which acts upon the upper side of the second piston member 8. A constant air pressure within the range 1-6 bars is set by means of the pressure reducing valve 28 so that an air volume sufficient to operate the piston member 6 is available within the vessel 3 and the cylinder arrangement 9 communicating with one another via the holes 14. The vessel 3 provides the correct amount of air at the correct pressure for operation, independently of the pressure in the fourth line 27, as long as this pressure exceeds the working pressure of the apparatus at least once during the operating cycle. In this state of the apparatus, no air is consumed. The three-way valve 30 is closed towards the vessel 3 and open towards the atmosphere for venting the piston arrangement 6. Water is supplied continuously through the first conduit 17 via the flow meter 22 which, independently * 5 of water pressures within the range 1-10 bars, gives a constant water flow. The water flow may in this case be 60 1/h. The water then flows through the non-return valve 23, the channel 15, the passage 19, the annular groove 21, the passage 19, and the channel 16 into the 0 second conduit 18. The water flows into the upper part of the dosing chamber 2 via the solenoid valve 24 and the non-return valve 25 and leaves the apparatus through the third conduit 26 at the same flow as in the conduit 17. The water pressure on the third piston member 20 5 falls short of the above-mentioned counteracting pressure on the piston arrangement 6. Reference is now made to Fig. 2a which illustrates the apparatus during dosing. For dosing, the solenoid valve 24 closes for about 1 min., and the water flowing 0 into the space between the piston member 20 and the partition 4 in the dosing chamber urges the third piston member 20, and thus the piston arrangement 6, upwards in the dosing chamber 2. At the same time, the dosing chamber is emptied in that the water therein above the 5 piston member 7 leaves the chamber at a constant flow through the conduit 26. In Fig. 2a, the movement of the piston members 7 and 20 is indicated by the arrow a. The desired fluid volume is set by timed operation of the solenoid valve 24 and is available in the upper 0 part.of the dosing chamber 2. Reproducibility is con¬ siderable because of the slow flow and the precision of the flow meter 22. The long dosing time renders the * dosing volume insusceptible to the a.c. crossovers. In the prior art apparatus referred to above, the solenoid 5 valve is activated for 0.1-0.3 sec, and the result is affected by about 1 Hz by the a.c. crossovers so that the dosed fluid volume varies by about 10%. Fig. 2b shows the apparatus during emptying of the dosed fluid volume. When the desired fluid volume has been obtained in the dosing chamber 2, the solenoid valve 30 is opened and air flows from the vessel 3 through the conduit 29 to the piston arrangement 6. The air passes through the central opening in the piston member 8, the bore 11 in the piston rod 10, the openings 12 and into the space between the piston members 7 and 20 in the dosing chamber. The air pressure thus acts upon the lower side of the piston members 8 and 7 and upon the upper side of the piston member 20. Since the solenoid valve 24 is still closed and the non-return valve 23 in the conduit 17 acts as a closing valve because the air pressure exceeds the water pressure in the conduit 17, the piston member 20 is not moved downwards because the space between the piston member 20 and the partition 4 and the channels 15 and 16 is water-filled, and water is incompressible. This means that the piston member 7 is moved upwardly in the dosing chamber 2, as shown by the arrow b in Fig. 26, emptying being effected through the conduit 26. Emptying is stopped mechanically in that the stop ring 13 on the upper side of the piston member 8 comes into contact with the lower side of the partition 4 within the cylinder arrangement 9. The length of the piston rod 10 is so chosen that, when the piston arrangement 6 is in its uppermost position, a space remains between the piston member 7 and the upper wall of the dosing chamber. The dosed fluid volume is dispensed during a short period of time, i.e. at a high velocity which can be controlled by regulating the pressure within the vessel 3, i.e. by means of the pressure reducing valve 28. Fig. 2c shows the apparatus during emptying of the remaining active fluid volume in the dosing chamber. For good reproducibility during dosing, or for special operating purposes requiring a constant flow at a flow fate different froπi that of the constant flows previously mentioned, the water volume enclosed between the piston member 20 and the partition 4 must be removed, which in this case is done in about 1 sec. after a pause of some tenths of a second. To this end, the solenoid valve 24 is opened so that the pressure of the air in the space between the piston members 7 and 20 within the dosing chamber 2 urges the piston member 20 downwardly towards the partition 4, as shown by the arrow £ in Fig. 2c. The valve 23 is still closed, and the water flows through the conduit 18 and the space between the piston member 7 and the upper wall of the dosing chamber out through the conduit 26. The solenoid valve 30 is still open and supplies air from the vessel 3 for oper¬ ating the piston member 20. The vessel has been dimen- sioned for an air volume sufficient to ensure reliable operation without interfering pressure drops. Fig. 2d shows the apparatus during filling of the dosing chamber, i.e. when the apparatus is returning to its normal state as shown in Fig. 1. After all of the water enclosed between the piston member 20 and the partition 4, or a sufficient volume thereof, has been discharged, the three-way solenoid valve 30 is closed towards the vessel 3 and opened towards the cyl¬ inder arrangement 9 to vent the piston arrangement 6, i.e. to remove the air pressure on the lower sides of the piston members 7 and 8. The piston members 7 and 20 are returned to their positions of rest, i.e. the state shown in Fig. 1 , by means of the water pressure within the dosing chamber 2 acting on the upper side of the piston member 7, and by means of the air pressure within the cylinder arrangement 9 acting on the upper side of the piston member 8. It should be noted that the valves 23 and 24 are open at this stage, and that water flows into the apparatus through the conduit 17 and into the channel 15 and the annular groove 21. Then the water, together with any water remaining in the space between the piston member 20 and the partition 4, flows through the conduit 18 at a substantially constant flow into the dosing chamber 2 and out through the conduit 26, simultaneously as the dosing chamber is being filled. At the end of the filling stage, the apparatus thus is in the state shown in Fig. 1, and the incoming water flow equals the outgoing water flow. All valve means are open, except for the solenoid valve 30 which is closed towards the container 3, but vents the piston arrangement 6. The apparatus as described above provides a constant fluid flow which is the same both in the normal state and during dosing. During emptying of the dosed volume, a short and powerful increase of the flow is achieved, and then a constant flow which is somewhat larger than the original flow, followed by a constant flow which is slightly less than the original flow, whereupon the original flow is reestablished. The invention is not restricted to the embodiment described above and illustrated in the drawing, but can be modified within the scope of protection as defined by the appended claims.

Claims: CLAIMS 1. A method for dispensing, during a short period of time, a predetermined volume of a fluid into a sub¬ stantially constant flow of said fluid, c h a r a c ¬ t e r i s e d in that it comprises introducing the fluid at a constant flow into a dosing apparatus via a first valve (23) and conducting it out of said dosing apparatus at the same flow via a conduit (18) having a second valve (24) communicating said first valve (23) with the dosing chamber (2) of said dosing apparatus, and via said dosing chamber (2); stopping the throughflow for a predetermined period of time by closing the second valve (24) in the conduit (18), whereby the fluid flowing into the dosing apparatus is allowed to flow into the dosing chamber and move a piston arrangement (6) movably mounted in said dosing chamber (2), such that fluid in the dosing chamber on the other side of said piston arrangement (6) is caused to leave the dosing apparatus at a constant flow, and whereby a desired fluid volume is dosed in said dosing chamber; causing the dosed fluid volume in the dosing chamber (2) to flow out of said dosing apparatus during a short period of time by means of the piston arrangement (6) when also the first valve (23) has been closed; causing fluid to flow out of said dosing apparatus at a constant flow via the conduit (18) and the second valve (24) and via the dosing chamber (2), fluid being prevented from flowing into the dosing apparatus in that the first valve (23) remains closed; and causing fluid to flow at a constant flow into said dosing apparatus by opening the first valve (23), and to flow through and leave said dosing apparatus via the conduit (18) and the second valve (24) and via the dosing chamber (2), whereby said dosing chamber (2) is filled and fluid flows out of said dosing apparatus at a substantially constant flow. 2. A method as claimed in claim 1, c h a r a c ¬ t e r i s e d in that, for dosing, use is made of the fluid flow into the dosing apparatus, together with timing when the first valve (24) is closed. 3. A method as claimed in claim 1, c h a r a c ¬ t e r i s e d in that a compressible medium under con¬ stant pressure is enclosed within the dosing apparatus and utilised for discharging the dosed fluid volume, the discharge velocity of the fluid being related to the pressure of said medium. 4. A method as claimed in claim 3, c h a r a c ¬ t e r i s e d in that, after the dosed fluid volume has been discharged, the compressible medium causes fluid to be discharged from said dosing apparatus at a constant flow via the conduit (18) and the second valve (24) and via the dosing chamber (2). 5. Apparatus for dispensing, during a short period of time, a predetermined volume of a fluid into a sub¬ stantially constant flow of said fluid, as claimed in claims 1-4, c h a r a c t e r i s e d by a body with a dosing chamber (2) and a vessel (3) for compressible medium, said dosing chamber and said vessel being sepa- rated by a partition (4) having a bore (5), a piston arrangement (6) having a first piston member (7) in sliding and sealing engagement with said dosing chamber (2), and a second piston member (8) in sliding and sealing engagement with a cylinder arrangement (9) in the vessel (3), said piston members (7, 8) being interconnected by means of a hollow piston rod (10) mounted in the bore (5) of the partition and having openings (12) in said first piston member (7), and said first piston member (7) having a cross-sectional area larger than that of said second piston member (8), a channel means (15, 16) formed in said partition and adapted to be connected, at one peripheral end, to a first conduit (17) for constant flow fluid supply and, at its other peri¬ pheral end, to a second conduit (18) communicating with the dosing chamber (2), a third piston member (20) freely movable between said first piston member (7) and said partition (4) and in sliding and sealing engagement with both the dosing chamber (2) and the piston rod (10), a first valve means (24) for controlling the fluid flow in said second conduit (18), a second valve means (30) for pressurised supply of a working medium to said piston arrangement (6), and a third conduit (26) for the fluid flow from the dosing apparatus. 6. An apparatus as claimed in claim 5, c h a r a c ¬ t e r i s e d in that the third piston member (20) has an annular groove (21) which is open towards the partition (4), and that said partition (4) has passages (19) connected to the channel means (15, 16) in said partition, said passages being open towards the third piston member (20) and facing the grooves (21) of the third piston member. 7. An apparatus as claimed in claim 5, c h a r a c ¬ t e r i s e d in that the vessel (3) communicates with the piston arrangement (6) via the second valve means (30). 8. An apparatus as claimed in any one of claims 5-7, c h a r a c t e r i s e d in that a first non¬ return valve (23) is mounted in the first conduit (17), and that optionally a second non-return valve (25) is mounted in the second conduit (18). 9. An apparatus as claimed in any one of claims 5-8, c h a r a c t e r i s e d in that a flow meter (22) is mounted in the first conduit (17), and that a timer is connected to the first valve means (24) and to the second valve means (30). 10. An apparatus as claimed in claim 5, c h a r a c - t e r i s e d in that the vessel (3) communicates, via a pressure reducing valve (28), with a compressed air source, and that said vessel (3) communicates with the interior of the cylinder arrangement (9) via holes (14) in the upper part of said cylinder arrangement.

Inventors: EKLOEF ULF, EKLOEF, ULF
Applicants: U & I ENG HANDELSBOLAG
Application year: 1989
Main classification: G05D7
IPC codes: G01F11