US3583423A - Dosing device for gaseous or liquid substances - Google Patents

Abstract

The invention relates to a dosing device for supplying or removing quantities of gaseous or liquid substances to or from a space. The dosing device is meant for dosing any desirable, not too large, quantity, for example, from a few cm.3 per second to a quantity zero, in which the pressure of the dosed quantity may be from less than 1 atm. to some tens of atmospheres.

Description

United States Patent l-llllebrand Johannes Josephus Kraakman Inventor Emmasingel, Eindhoven, Netherlands Appl. No. 858,444 Filed Sept. 16,1969 Patented June 8, 1971 Assignee U. S. Philips Corporation New York, N.Y. Priority Sept. 18, 1968 Netherlands 6813306 DOSING DEVICE FOR GASEOUS 0R LIQUID SUBSTANCES 2 Claims, 1 Drawing Fig.

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[56] References Cited UNITED STATES PATENTS 3,411,416 11/1968 Herd 137/117 3,320,968 5/1967 Nuss 137/117 Primary Examiner-William F. O'Dea Assistant Examiner-William H. Wright A!t0rneyF rank R. Trifari ABSTRACT: The invention relates to a dosing device for supplying or removing quantities of gaseous or liquid substances to or from a space. The dosing device is meant for dosing any desirable, not too large, quantity, for example, from a few cm. per second to a quantity zero, in which the pressure of the closed quantity may be from less than 1 atm. to some tens of atmospheres.

PATENTEU JUN 8 I971 I Z TOR. HILLEBRAND J,J- KR KMAN AGEN DOSING DEVICE FOR GASEOUS R LIQUID SUBSTANCES It has this far been difficult to produce such a dosing device, because the component parts must meet very high standards, and the adjustability, presents great difficulties. The device according to the invention however, is simple to manufacture and the adjustability of the supplied quantity is also simple since no spindles, valves or the like are required. Moreover, both the supply and the removal of the dosed quantity to and from a space can be produced with the same device.

According to the invention, a dosing device as described above is characterized in that a cylinder comprises a piston assembly consisting of two pistons of the same diameters, between which a piston of a larger diameter is situated and chambers are situated between the pistons. One of the two pistons, having equal diameters, and the piston having the larger diameter, have a circumferential groove on their circumference. A communication duct for the substance to be dosed opens into the two chambers, a communication duct debouching near each of the free end faces of the pistons having the same diameters, in one of which an adjustable control pressure prevails, the other duct communicating with the ambient pressure. The largest piston situated in the center of the piston assembly has on its circumference at least one axial slit which forms a communication, depending upon the axial position of the piston assembly, of an adjustable size between the chamber which is situated near the piston, which does not comprise a circumferential groove, and an annular space present in the cylinder wall. This space communicates with a duct for removing the substance to be dosed. Open communications are provided between the two annular grooves present on the said pistons, and the chamber in which the slit opens. The pressure in the chamber with which the slit communicates is regulated by the position of the piston assembly in the cylinder. This pressure also prevails in the two annular grooves, whereas in the other chamber the pressure prevails of the desirable volume flow, said other chamber communicating, through a narrow gap formed between the piston parts and the cylinder wall parts of both the larger and the smaller diameters, with the two circumferential grooves in which the regulated pressure prevails.

When temperature variations occur in the volume flow to be dosed or when the device is to be used in a space in which varying temperatures occur, according to a further embodiment of the invention, the various elements of piston assembly and the cylinder are made of materials having different coefficients of expansion, so that upon temperature variations, the variation of the gap height compensates for the change of the viscosity of the liquid or the gas.

In order that the invention may be readily carried into effect, one example of the invention will now be described in greater detail, by way of example, with reference to the accompanying drawing, the sole FIGURE of which shows a cross-sectional view of a cylinder with piston assembly which is arranged therein so as to be axially movable.

Reference numeral 1 in the drawing denotes a cylinder to which a cylinder cover 2 is secured. On the right-hand side, three communication possibilities 3, 4 and 5 are shown; on the left-hand side a fourth communication possibility 6 is shown in, the cover 2. The cylinder 1 comprises a piston assembly consisting of two equal pistons 7 and 8, having diameters d, and a larger piston 9, having a diameter D, between the pistons 7 and 8. The piston 7 has an annular groove 10; the piston 9 has a similar groove 11. Between the end face of the piston 7 and the cover 2, a chamber 12 is situated; furthermore, a chamber 13 is situated between the cover 2 and the other side of the piston 9. Similar chambers which are denoted by 14 and 15 are situated between a side face of the piston 9 and the cylinder 1 and between the end face of the piston 8 and the end ofthe cylinder.

Centrally located in the piston assembly a duct 16 is provided which is in open communication, through apertures l7,

l8 and 19, with the annular grooves 10 and I1 and with the chamber 14. These consequently communicate with each other the same pressure prevailing in each. A duct 20 which is in open communication with the chamber 13, through a duct 21, opens into the connection possibility 3. The connection possibility 5 communicates with the chamber 14, through a duct 22. In the circumference of the piston 9 four slits 23 are provided; these slits open on the one hand into the chamber 14 and produce a communication with an annular space 24 in the cylinder wall having a size which is dependent upon the position of the piston assembly. The annular space 24 communicates through a duct 25 with the ambient pressure. The gap between the circumferences of the pistons and the respective cylinder walls lies in the order of magnitude of 20 .t.

The operation of the dosing device will now be described for a volume flow emerging from the duct 20, for example, a flow of oil, in which a desirable supply can be realized between a few cm per second and zero. An oil duct communicates with the connection 6, at a pressure p; which will be termed control pressure. It should be possible to adjust said pressure in accordance with the desirable supply, for example, at high-pressure level with a pressure regulating valve and at low-pressure level, for example, with a liquid column. An oil duct communicates with the connection possibility 5 at a pressure, the value p: of which is regulated in chamber 14, by the overlap of the slits 23 and the annular space 24. For a volume flow emanating from the duct 20 the regulating pressure p is larger than the pressure p,. The pressure p prevails in the chamber 12, since there is an open communication through duct 22, duct 16, and apertures l7, l8 and 19. However, the emanating pressure 1 prevails in the chamber 13, since said chamber is in open communication with the emanating aperture 3. Owing to the pressure difference ga -p, between the annular grooves 10 and 11 on the one hand, and the chamber 13 on the other, a laminar flow occurs in the two annular gaps 26 and 27. The differential pressure p p follows from the equilibrium of forces of the piston assembly, namely:

1 2 'I 2 2 'I z. 2 P +P 2 From this it follows that It is found that with given D and d, the differential pressure between p and p is only dependent upon the pressure 1 As is known, the supply through a laminar resistor of the type as is formed by the gaps 26 and 27 is linearly dependent upon the differential pressure across said resistance according to the equation known from fluid dynamics:

wherein l is the supply, D the diameter, H the gap height, p. the viscosity and L the gap width. For a dosing device of the type described having given dimensions and for a given liquid it holds at substantially constant temperature that =C(p p wherein C is a constant. The supply to be dosed is hence only determined by the value of p (for this is, proportional to p -p Since p; can be adjusted at any desirable value, any desirable small supply can be adjusted. The above consideration is correct at a constant temperature of the oil and of the ambient pressure. When temperature variations occur this results in a variation of the viscosity of the oil, so that hence the supply varies. This supply deviation as a result of the deviation in viscosity can be compensated for by making the gap height H in gaps 26 and 27 likewise a function of the tem perature, so that H /ufrom the supply formula for laminar flow likewise remains constant. This can be realized with a suitable choice of the material of the cylinder and the piston assembly. A suitable choice of the dimensions of the piston diameter and the gap height can also contribute to suppressing supply variations as a result of temperature influences.

When a comparatively high-pressure p and hence also p,, is used, it may be desirable to arrange a second cylinder around the cylinder 1. which second cylinder encloses the cylinder on both sides, and to supply therein the same pressure p so that likewise said pressure p is exerted on the circumference of the cylinder ll.

in the embodiment described the dosed quantity is supplied to a space; when this quantity has to be removed from a space, the duct in which the pressure p prevails is connected to the communication 4 and communication 6 remains open.

I claim:

1. A dosing device for supplying or removing quantities of liquid or gaseous substances to or from a space, characterized in that a piston assembly is present in a cylinder and consists of two pistons of equal diameters, between which a piston of a larger diameter is situated and chambers are situated between the pistons, one of the two equal pistons and the piston having the larger diameter comprising on their circumference a circumferential groove, a communication duct for the substance to be dosed opening into the two chambers, a communication duct opening near each of the free end faces of the pistons having equal diameters in one of which an adjustable control pressure prevails, the other duct communicating with the ambient pressure, the largest piston situated in the center of the piston assembly comprising on its circumference at least one axial slit which forms a communication of an adjustable size. which is dependent upon the axial position of the piston assembly, between the chamber which is situated near the piston which does not comprise a circumferential groove and an annular space present in the cylinder wall, which space communicates with a duct for removing the substance to be dosed. open communications being present between the two annular grooves present on the said pistons, and the chamber into different coefficients slit opens, the pressure in the chamber with which the slit communicates being regulated by the position of the piston assembly in the cylinder, said pressure also prevailing in the two annular grooves, the pressure of the desired volume flow prevailing in the other chamber, said other chamber communicating by means of a narrow gap formed between the piston parts and the cylinder wall parts of both the larger and the smaller diameters, with the two circumferential grooves, in which the regulated pressure prevails.

2. A dosing device as claimed in claim 1, characterized in that the materials of which the piston assembly and the cylinder consists, have different coefficients of expansion, so that upon temperature variations, the variation of the gap height compensates for the variation of the viscosity of the liquid or the gas.

um'rrzu S'IA'IES IA'IEN'I UFFILI'I CERTIFICATE OF CORRECTION Patent No. 3 583 ,423 Dated June 8, 1971 Inventor) HILLEBRAND JOHANNES JOSEPHUS KRAAKMAN It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

P- IN THE CLAIMS Claim 1, line 22; delete "dif";

line 23. delete "ferent coefficients" and insert -which the-.

Signed and sealed this 2nd day of January I973.

(SEAL) Attcst:

IZDWARI) I I.FLETCIIIZR,JR.

Commissioner of Patents

Claims (2)

1. A dosing device for supplying or removing quantities of liquid or gaseous substances to or from a space, characterized in that a piston assembly is present in a cylinder and consists of two pistons of equal diameters, between which a piston of a larger diameter is situated and chambers are situated between the pistons, one of the two equal pistons and the piston having the larger diameter comprising on their circumference a circumferential groove, a communication duct for the substance to be dosed opening into the two chambers, a communication duct opening near each of the free end faces of the pistons having equal diameters in one of which an adjustable control pressure prevails, the other duct communicating with the ambient pressure, the largest piston situated in the center of the piston assembly comprising on its circumference at least one axial slit which forms a communication of an adjustable size, which is dependent upon the axial position of the piston assembly, between the chamber which is situated near the piston which does not comprise a circumferential groove and an annular space present in the cylinder wall, which space communicates with a duct for removing the substance to be dosed, open communications being present between the two annular grooves present on the said pistons, and the chamber into different coefficients slit opens, the pressure in the chamber with which the slit communicates being regulated by the position of the piston assembly in the cylinder, said pressure also prevailing in the two annular grooves, the pressure of the desired volume flow prevailing in the other chamber, said other chamber communicating by means of a narrow gap formed between the piston parts and the cylinder wall parts of both the larger and the smaller diameters, with the two circumferential grooves, in which the regulated pressure prevails.

2. A dosing device as claimed in claim 1, characterized in that the materials of which the piston assembly and the cylinder consists, have different coefficients of expansion, so that upon temperature variations, the variation of the gap height compensates for the variation of the viscosity of the liquid or the gas.

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