US2921715A - Solenoid operated microburette - Google Patents

Description

Jan. 19, 1960 G. M. ASSET ETAL 2,

SOLENOID OPERATED MICROBURETTE Filed March 18, 1959 n INVENTORS Gabriel/e Asset Bernard F Mc Namara B; 4 EMM ATTORNEY United States Patent Office 2,921,715 Patented Jan. 19, 1960 Namara, Joppa, Md., assignors to the United States of America as represented by the Secretary of the Army Application March 18, 1559', Serial No; 800,348

(Granted under Title as, US. Code 1952 see. 266) The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment to us of any royalty thereon.

This invention relates to a microburette for producing droplets of controllable size. It is an improvement on that described by W. R. Lane, Journal of Scientific Instruments, vol. 24, pp. 98-101 (1947). Our device is so coristructed that it may be used to produce either a single droplet or a continuous series of droplets of substantially the same size. The size can be accurately controlled.

The drawing is a diagrammatic view of our apparatus.

A fine hypodermic needle 1 about 25 to 27 gauge is attached to the end of a capillary tube 3 and passes vertically through the airfiow block 5. The slip joint 7 of the needle is seated in the block and the point 9 of the needle protrudes through a circular aperture 11 about one-half inch. The airflow block provides for a passage of air flow from a solenoid operated valve 13 through the circular aperture 11 which forms an annular air jet around the needle 1.

The capillary tube 3 has a fine bore of approximately 0.5 mm. and comprises two vertical arms, a shorter one 15 and a longer one 17 connected by a horizontal portion 18. The shorter arm 15 is attached to the slip joint 7 of needle 1 while the longer arm 17 is sealed in reservoir 19 which holds the liquid 20 from which the droplets are formed. It will be noted that arm 17 extends nearly to the bottom of reservoir 19 so that its open lower end is below the level of liquid 20. Arm 17 and reservoir 19 are so proportioned that the level of liquid 20 is always below the level of tip 9 of needle 1. This prevents siphoning. Inlet 21 of reservoir 19 is connected through a metering valve 23 and a pressure regulator 25 to a source of compressed filtered air 26, having a source pressure of about lbs. per sq. in.

The solenoid valve 13 is also connected through metering valve 27 and pressure control 29 to the source 30 of compressed air which may have a pressure of about 30 lbs. per sq. in. Pressure control 29 is adjusted to give a superatmospheric pressure of less than 10 lbs. per sq. in. at solenoid valve 13, which is quick acting in this pressure range. The solenoid 31 which activates valve 13 has a strong spn'ng return 33. Consequently, valve 13 admits a sudden pulse of air to air flow block 5 when solenoid 31 is energized and cuts the air flow off sharply when current is discontinued.

The solenoid may be actuated either automatically or manually. In automatic operation the solenoid is controlled by a cam-operated switch 35, the lever arm of which rises and falls as the follower of cam 37. The periphery of cam 37 is provided with a groove or indentation 39. The cam is rotated by motor 41. The duration and frequency of the air pulse are determined by the width of groove 39 and the rate of rotation of cam 37.

To secure proper control, it is desirable that the width of groove 39 be variable. To this end, it is desirable that cam 37 be one of the well known adjustable split cams which are commonly used in connection with time switches of various types. Alternatively, the cam may be so mounted as to be readily removed and replaced, or a plurality of cams may be mounted on the motor shaft and the latter made longitudinally adjustable.

Means are also provided for manual control of the solenoid valve. A key, 43, may be used. Alternatively a manually rotated cam may be provided to actuate switch 35.

Regulators 25, 29 provide the basic regulation of the pressure in the reservoir 19 andv at the solenoid valve 13, respectively. Manually controlled metering valves 23, 27 provide for the fine control of these pressures. The pressures at the various points are indicated by pressure gauges 45 and 47 and by manometer 49, having reservoir 51. Provision of a small leak 52 permits a slight how of air at all times through valve 23 and gives better control of the pressure. By these controls and gauges, it is possible to keep conditions the same from day to day. Electric counter 53 counts the number of pulses delivered by solenoid valve 13.

Operation Reservoir 19 is filled with liquid 20 to about the depth indicated in the drawing. Pressure is then applied to the reservoir in an amount just sufficient to cause the liquid to flow through the capillary tube 3 and slowly form a drop at the point 9 of needle 1. The air pressure in the reservoir is then carefully reduced until no drops form at the point of the needle but the surface of the liquid is visible in the lumen of the point. Under these conditions the total pressure on the surface formed on the lumen of the point and the surface tension are in equilibrium with the forces due to the difierences of the levels of the liquid in the two arms, 15, 17 of tube 3 and the air pressure in reservoir 19. With the proper air pressure at solenoid valve 13, and the proper width of the groove 39 of cam 37, rotation of the cam by motor 41 causes a pulse of air to flow through air flow block 5 and the circular aperture 11 surrounding the needle 1. This upsets the equilibrium of pressures on the surface of the liquid at point 9 of the needle. A fine filament is drawn out of the liquid in the air jet and a portion is broken off and forms a drop. The size of the drop is determined by the pressure on the liquid 21 in reservoir 19, the duration of the air pulse and the volume of the air in the pulse, the latter being governed by the pressure at solenoid valve 13. This mode of operation, i.e., initial adjustment of the pressures until the forces are at equilibrium at the point of needle 1, produces the smallest sizes of drops.

To increase the size of the drop, the pressure in reservoir 19 is increased. The pressure may be made such that a drop grows very slowly atthe tip of the needle. The air jet blows the drop off the point before it falls under its own weight. The drop size is determined by the pressures and the timing of the air pulse. The duration and volume of the air pulse must be controlled to prevent scattering of the drop.

The initial determination of the conditions to produce drops of a given size is made experimentally. Once they are determined, reproducible results can be maintained by keeping the same indicated pressures on manometer 49 and the pressure gauge 47 and the same timing of solenoid valve 13. The operation of the valve is, in turn,

determined by the speed of motor 41 and the width of groove 39 of cam 37.

By the use of a manually controlled switch such as key 43 or the other arrangements described above single drops can be released. By the automatic control of the switch, an extended series of drops of uniform size, uniformly spaced in time, can be produced. By the variasiderable range in size of drops is possible. We have produced uniform drops singly and in series in the range 0.500 to 0.130 mm.

We claim: 7 W v V 1. Apparatus for producing droplets of Controllable size comprising a closed reservoir, a capillary discharge tube having an inlet communicating with said reservoir near the bottom thereof, said discharge tube terminating in a downwardly directed fine-bored tip, an air supply tube communicating with said reservoir at a point above said inlet, whereby said reservoir is adapted. to retain a body of liquid between said inlet and said air supply tube, said tip being positioned at ca level, above'that of said airrsupply tube,'first air supply means adapted to supply air under superatmospheric pressureto said air supply tube, control means associated withsaid first air supply means and adapted to accurately control the pressure of the. air delivered to said air supply tube an air flow block defining a. downwardly directed aperture surrounding said tip, second air supply means adapted to supply air under superatmospheric pressure to said air flow block, said second air supply means comprising a quick' acting solenoid valve "adapted to quickly admit air to said block and then quickly shut oflE said air, control means adapted to deliverjair to said air flow block through said, solenoid valve underaccurately controlled pressure, and electric switching means adapted to energize said solenoid valve. f

2. Apparatus as defined inclaim 1 wherein said electric switching means comprises 'a switch arid a motor driven cam arranged to periodically open and close said switch.

References Cited iri the'fil'of this patent W. R. Lane: Iournaljof Scientific Instruments, vol. 24, January 1947, pp. 98-1-1, published by the Institute of Physics, 47 Belgrave Square, London, S. W.l

Images