US3106190A - Reservoir for writing or dispensing instruments - Google Patents

Description

Oc 8, 96 H. R. FEHLING EIAL 3,106,190

RESERVOIR FOR WRITING OR DISPENSING INSTRUMENTS Filed July 20, 1961 2 Sheets -Sheet 1 INVENTORS HANS REINHARD FEHLING 8| EDWARD HENRY HARVEY heir ATTORNEYS 1963 H; R. FEHLING ETAL 3,106,190

' RESERVOIR F'OR WRITING 0R DISPENSING INSTRUMENTS Filed July 20, 1961 2 Sheets -Shee t, 2

INVENTORS HANS REINHARD FEHLING 8 EDWARD HENRY HARVEY their ATTORNEYS United States Patent 3,106,190 RESERVOIR FOR WRITlN G OR DISPENSING INSTRUMENTS Hans Reinhard Fehling, Zug, Switzerland, and Edward Henry Harvey, London, England, assignors to I.R.C. Limited, London, England, a company of Great Britain Filed July 20, 1961, Ser. No. 125,551 Claims priority, application Great Britain July 30, 1960 12 C. (Cl. 120-424) This invention relates to liquid reservoirs for writing or other dispensing instruments and, more particularly, to a new and improved liquid reservoir for liquids of relatively low viscosity.

This application is a continuation-impart of our copending application for Seal for Reservoirs of Writing and Other Dispensing Instruments, Serial No. 5,872, filed February 1, 1960. In our copending application there is described a seal for a liquid reservoir having a bore open at one end to the exterior of the reservoir and a dispensing device such as a writing tip communicating with the other end of the bore comprising a piston follower slidable in the bore and forming a clearance space of capillary dimensions therewith, along with means for urging the follower in the direction out of a liquid contained in the reservoir so as to oppose the capillary force of a liquid meniscus in the clearance space surrounding the follower which tends to draw the follower into the reservoir liquid. In one of the embodiments described in the copending application the urging means is acompression spring located within the reservoir while in another embodiment the urging means is a tension spring extending from the follower to the reservoir at a point near the open end of the bore.

In all of the embodiments described in the copending application and in most conventional ball-point writing instruments the weight of the liquid column when the reservoir is in the upright position produces a liquid pressure or head at the writing tip which tends to force liquid out of the tip. With relatively viscous and quick drying inks of the type now used in ball-point pens, which have a viscosity of about one hundred poise at 25 C., practically no ink flows through the tip before the ink at the tip dries to form a seal. If a non-drying or slow drying ink or a less viscous ink is used in a conventional reservoir, however, objectionable leakage of ink through the writing tip can occur when the reservoir is in the upright position because of the pressure produced at the tip by the weight of the liquid column.

Accordingly, it is an object of this invention to provide a new and improved liquid reservoir for dispensing instruments which overcomes the above-mentioned shortcomings of conventional reservoirs.

Another object of the present invention is to provide an improved reservoir for dispensing instruments especially adapted to hold liquids of relatively low viscosity.

A further object of the invention is to provide a reservoir of the above type wherein the liquid pressure at the dispensing end remains substantially constant as liquid is withdrawn from the reservoir.

These and other objects of the invention are accomplished by providing a reservoir with a supply conduit having a bore which is open at one end to the exterior of the reservoir and a discharge duct which leads from the other end of the bore to a dispensing extremity located farther from said other end of the bore than is the open end in a direction opposite to the direction from the open end to the other end of the bore. In addition, the reservoir is provided with a piston which is slidable in the bore and forms a clearance space of capillary dimensions therewith and .with means for urging the piston toward the open end of the bore with increasing force as the piston moves away from the open end but with insufficient force to drive the piston out of a liquid contained in the bore. In one embodiment of the invention the urging means comprises a compression spring located within the bore and the change in spring force per unit change in length of the spring is approxi materialy equal to the change in the liquid pressure or head at the dispensing extremity resulting from withdrawal of liquid from the reservoir.

Further objects and advantages of the invention will be apparent from a reading of the following description in conjunction with the accompanying drawings, in which:

FIGURE 1 is a view in longitudinal section through a typical writing instrument having a reservoir arranged accordingto the present invention;

FIGURE 2 is a view in longitudinal section through a complete hand writing instrument incorporating a reservoir according to this invention;

IFIGURES 3 and 4 are cross-sectional views taken respectively on the lines lII-III and IVIV in FIG- URE 2;

FIGURES 5, 6 and 7, respectively, are views in longitudinal section through three further instrument units according .to this invention; and i FIGURE 8 is a fragmentary view showing another type of reservoir follower according to the invention.

While the present invention is applicable to reservoirs of writing instruments such as fountain pens, stylographic pens, and ball-pens and ball-point pens, it is also applicable to dispensing instruments or applicators (primarily those having a ball-tip or ball-valve discharge end) such ,as may be used for dispensing or applying deodorants,

scent and other, cosmetics. It is especially applicable to the reservoirs of ball-point writing instruments, for the difiiculties which the invention seeks to reduce have chiefly arisen in connection with ball-point writing instruments. Accordingly, the invention is described herein with reference to ball-point writing instruments.

Turning now to FIGURE 1 the reservoir 10 (constituting a supply duct having a bore open at one end to the exterior of the reservoir) contains a column 11 of ink or other liquid to be dispensed and at the head of this column there is a slidable piston or follower 12 which is urged toward the open, or vented, end 13 of the reservoir by a compression spring 14 contained within the reservoir. The liquid 11 fills the narrow annular gap or clearance between the periphery of the follower 12 and the interior of the reservoir 10 and the spring 14 exerts on the follower 12, in all attitudes of the reservoir, a force which is so directed that it tends to urge the follower out of the reservoir liquid in which it is wholly or partly immersed andbeing large enough to balance in any attitude of the reservoir all other forces which tend to urge the follower further into the liquid. If desired, a sealing liquid different from the reservoir liquid may be provided in the clearance about the follower 12.

In a conventional reservoir utilizing a piston follower to form the seal, one end or face of the follower is immersed in the liquid whilst the other end or face (which is subject to atmospheric pressure) emerges from it with the result that at the latter end a small meniscus is formed at the surface of the thin annulus of liquid filling the clearance between the follower periphery and the reservoir Wall.

If this meniscus is concave, the resulting capillary forces produce a depression (below atmospheric pressure) in this annulus of liquid. In consequence there is a pressure difference between the two faces or ends of the follower which, even if the latter has the same bulk density (apparent specific gravity) as the liquid, tends to force the follower into the liquid.

If this force is not balanced by an opposing force, the follower will move into the liquid and extrude the latter through the above-mentioned annular clearance. This condition occurs when the reservoir lies on its side. Movement of the follower into the liquid will continue until the concave meniscus changes its shape in such a way that the resulting capillary forces no longer reduce the hydrostatic pressure in the reservoir, i.e., when in effect the pressure difference between the two ends of the follower has vanished. The capillary pressure can only decrease if the radius of the meniscus increases, i.e., if a strong, stable meniscus changes into a weak and usually unstable meniscus, whether slightly convex or slightly concave. When this happens there is danger of liquid seepage toward the rear end of the reservoir, especially if there already exists a film of liquid on the reservoir wall behind the follower (as may happen due to the liquid level being lowered by the dispensing of liquid).

There is another and additional reason'why there is danger of seepage. When the reservoir is lying on its side, the annulus of liquid between the follower periphery and the reservoir wall, at the lower part of the follower periphery, is subjected to a positive hydrostatic head the magnitude of which is proportional to the diameter (or equivalent dimension) of the reservoir. Hence it is at this lower part of the follower periphery that liquid seepage takes place, unless the hydrostatic head at each point of the annular surface of the liquid is balanced by the local capillary pressure (depending on the local radius of curvature of the liquid surface).

In this specification the expression strong meniscus is used to indicate a meniscus which is very stable (and not one where the surface tension force is particularly high, for surface tension is constant and independent of curvature) the most important feature producing stability is a small radius of curvature, because such a meniscus will not practically change its shape in various positions of the instrument.

Accordingly, as described in the above-mentioned copending application, the spring 14 balances the capillary pressure by urging the follower 12 out of the reservoir liquid with a force which is sufficiently high to prevent seepage of liquid past the follower but is not higher than the forces on the follower resulting from the formation of a liquid meniscus in the annular clearance.

In a liquid reservoir of the type described herein it may also be desirable, or even essential, that the head under which the liquid is dispensed (or fed to the writing extremity) varies but little, or even remains substantially constant, while the reservoir empties. In a normal fountain pen the problem of maintaining substantially constant liquid pressure at the writing point is solved by allowing the air which replaces the ink to move up into a closed reservoir through the same channel as that through which the ink flows down. The result is that the head of liquid in the reservoir is approximately balanced by the air pressure in the reservoir which is, or should be, slightly below atmospheric. However, it is well known that this system is sensitive to changes in temperature and pressures of the surrounding atmosphere and that a normal fountain pen is particularly liable to leakage in modern air travel unless certain precautions are taken. As will be appreciated from the ensuing description a reservoir according to the present invention is less prone to leakage due to temperature and pressure variations.

In accordance with the present invention, therefore, the liquid reservoir is provided with means for exerting on the follower, at least in the operative attitude of the reservoir, a force which opposes movement of the follower along the bore as the liquid is discharged and increases with the distance travelled by the follower but is insufficient to eject the follower from the liquid, and with a discharge conduit leading from the rear end of the bore in a direction opposite to the said travel of the I a follower. The expression opposite is used in a broad sense to indicate that if the-bore is upright, or extends upwards, the discharge conduit extends in a downwards direction, for which purpose the discharge conduit may be parallel to, or at an angle to, the bore.

In the embodiment shown in FIGURE 1, there is a discharge conduit 15 leading from the inner end of the reservoir bore (toward which the follower =12 moves as liquid is dispensed) in a direction opposite the travel of the follower. The conduit 15, which is preferably of small diameter, terminates in a ballpoint writing extremity 16 located beyond the open end 13 of the bore. It will be appreciated that since the movement of the follower along the bore is opposed by the force of the spring 14-, which increases with the distance travelled by the follower 12, and the discharge conduit leads in a direction opposite to the follower travel, the capillary pressure set up by said force tends to nullify the variation in head that would otherwise occur at the writing extremity 1-6 as the length of the liquid column 11 in the bore decreases upon discharge through said conduit. Indeed if the rate of change of the capillary pressure set up by said force (per unit length of the bore) is equal to the rate of change of the liquid head, the two cancel one another and delivery under a constant or substantially constant head is achieved. To accomplish this the spring rate or stiffness is made equal to the rate of change of liquid head in the reservoir. The spring rate is the change in spring force per unit change in length of the spring: the rate of change of liquid head is the change in hydrostatic thrust on the foilower per unit change in the length of the liquid column.

Considering the writing instrument in the typical writing attitude shown in FIGURE 1 in which the reservoir 10 extends upwards, and the discharge conduit 15 downwards, at angle H, it can be shown that, if the spring rate is equal to the rate of change of liquid head, then throughout the life of the reservoir (i.e., irrespective of the volume of ink remaining in the reservoir) the head of ink at the writing extremity is constant and, in partitcular, that, at a given point in the discharge conduit 15, indicated at C in FIGURE 1, the pressure is equal to the atmospheric pressure.

In our aforesaid copending application it has been shown that the spring exercises an outward thrust on the follower which is balanced by the capillary forces of the meniscus set up between the follower and the reservoir walls. This capillary pressure is, in effect, equivalent to a negative head of liquid which increases as the reservoir empties, because the spring becomes more compressed and the outward throust increases correspondingly.

In the attitude shown in FIGURE 1 the positive head of liquid in the discharge conduit 15 is partly balanced by the negative head of liquid in the reservoir 1% itself. This negative head is assisted by the capillary pressure produced by the outward thrust of spring 14. As the reservoir 10 empties the negative head due to the liquid column in the reservoir diminishes, whereas the negative head due to the capillary pressure increases because of the increased outward thrust of the spring. If the spring is suitably designed, these variations will just cancel one another so that the total negative head opposing the constant positive head in the discharge conduit 15 remains constant. For this purpose the spring rate is made equal to the rate of change of liquid head in the following manner:

S=AW sin H (1) in which S is the spring rate (gm/cm.) A the cross-sectional area of the piston (cm?) W the specific gravity of the liquid H the angle of the reservoir in the normal position of use.

In order to achieve the correct spring rate according to this condition, the wire diameter of the spring has to be chosen according to the following formula:

in which a is the diameter of the wire (cm.)

B is the diameter of the spring (cm.)

n the number of turns of the spring G the rigidity modulus of the wire material (gm./cm.

The directions for determining the minimum and maximum outward thrust which the spring 14 should exert on the follower 12 in order to prevent leakage, as well as to prevent any instability of the annular meniscus, are set out in detail in the above-mentioned copending application. These directions, together with the spring rate as determined according to Formula 1, govern the usable length L of the ink column shown in FIGURE 1.

In order to determine the design factors controlling the head under which the liquid is to be dispensed, it is best first to determine at which point along the length of the discharge conduit 15 the head should be zero under the combined influence of the head of liquid in the reservoir and the negative head produced by the outward thrust of the spring 14 on the follower 12. In the particular embodiment shown in FIGURE 1, the position of this balance point is indicated at C. The desired balance is achieved if the length of the liquid column in the discharge conduit 15 down to the point C is equal to the free uncompressed length L of the spring 14 plus the length L of follower 12 (assuming the overall specific gravity or bulk density of the latter is equal to that of the liquid 11) e If the spring is then compressed by an amount required to establish a stable meniscus by the minimum outward thrust on the follower, the balance point C remains Where it was provided the spring rate is designed according to Formula 1. Hence if the writing extremity 16 were arranged to be at the balance point C, the head would remain zero while the reservoir empties. On the other hand, if a slight constant head is required, this can be easily achieved by adjusting the total length of the discharge conduit accordingly to provide an arrangement such as that shown in FIGURE 1. This is, of course, only strictly true for one attitude of reservoir 10 and discharge conduit 15, for the head will in fact vary slightly according to the angle H at which the instrument is held, but the variations are small and usually negligible. It will usually be best to design the instrument in such a way that the maximum permissible or desirable head is obtained in the upright position so that any more inclined position will automatically result in lowering the total head.

It will be noted that in an instrument according to the invention, there is no necessity to allow the ingress of air into the reservoir in order to achieve the balance desired. Hence, such an instrument is entirely insensitive to external changes in temperature and pressure. This is, of

course, highly desirable in any writing instrument, but

particularly in those using rather fluid inks.

The following data are given by way of example, for a typical ball-point pen according to the invention, assumming a normal use at an angle of 45 degrees:

Mean radial clearance mm 0.05

6 Length of ink column in full reservoir, L cm 5 Length of feed capillary to balance point, L-t-L About cm" 7.5 Total length of instrument, L cm 10 Head of liquid at the ball point (at 45 inclination) About cm 2 It will be appreciated that the reservoir unit shown in FIGURE 1 may be fitted to the barrel, case, or housing, of a hand writting instrument, and one manner of incorporating an equivalent unit in such a case or housing is illustrated FIGURES 2-4. It may here be mentioned that the units shown respectively in FIGURES 2-4, FIG- URE 5, FIGURE 6, and FIGURE 7, are basically similar to that shown in FIGURE 1. Therefore, in each of these five units like parts have like reference numbers with the addition of the index letter a in FIGURES 2-4, b in FIGURE 5, c in FIGURE 6, and d in FIGURE 7.

Turning now to FIGURES 2-4, the unit 17 shown therein has a reservoir 10a, ink column 11a, piston or follower 12a, spring 14a, discharge conduit 15a, and writing extremity 16a. It will be seen that the unit 17 is so applied to the shaft or casing 18 of the instrument that the reservoir 10a lies in the interior of the casing but that the discharge conduit 15a (with its reduced forward extremity 15a terminating in the writing extremity 16a containing the writing ball 19) lies in a longitudinal groove in the exterior of the shaft 18. A vent for the reservoir is shown at 21. In accordance with the copending application of Fehling and Street, Serial No. 87,821, filed February 8, 1961, and assigned to the same assignee as the present application, the part 15'a is so ben-t that (a) the ball 19 is disposed at or near the longitudinal axis 20 of the instrument 20 and preferably has a slight trail, and (b) the end portion of part 15a and at least the adjacent part of its bend are exposed at the surface of the shaft or casing 18 to the view of the user in the act of writing. For full directions on these matters reference is to be made to the above-identified application of Fehling and Street.

Suitable dimensions in one example according to FIG- URE 2 are as follows:

Reservoir bore (D) mm 6 Length of uncompressed spring (L) mm 61 Mean diameter of turns mm 4.75 Number of turns (n) 41 Wire diameter for brass (a) mm 0.11 Spring stiffness (S) gm./cm 0.19 Specific gravity of ink 1.1 Length of piston (L mm 8 Mean radial clearance mm 0.05 Length of ink column in full reservoir (L cm 3.5 Length of feed capillary to balance point (L+L,,)

About cm 7.5 Total length of instrument (L cm 9.7 Head of liquid at the ball-point (at 45 inclination) About cm- 1.6

In the modified unit 22 shown in FIGURE 5, the discharge conduit 15b extends, concentrically with the bore of the reservoir 10b, along the axis 10' of the latter. The follower 12b is therefore of annular form so as to slide along the annular cavity between the exterior of the conduit 15b and the bore of the reservoir 10b, the necessary clearance between the interior periphery of the follower 12b and the exterior periphery ofconduit 15b and between the exterior periphery of the follower and the bore of the reservoir being provided. Each clearance annulus is occupied by sealing liquid (being, conveniently, the reservoir liquid) which presents a meniscus towards the air space at the lower end of the follower, which space is vented at 21b.

Suitable dimensions in one example are as follows:

Reservoir bore (D) mm 5 Piston outside diameter mm 4.9

Piston inside diameter Q. mm 2.1 Discharge conduit outside diameter mm 2.0 Discharge conduit internal diameter mm 1.5 Mean radial clearance mm 0.05 Cross-sectional area of piston cm. 0.154 Length of piston mm 6 Length of uncompressed spring (L) mm 61.5 Mean diameter of turns mm 4.75 No. of turns (it) 65 Wire diameter for brass (a) mm 0.11 Spring stiifness (S) grn./cm 0.12 Specific gravity of ink 1.1 Length of ink column in full reservoir (L mm 43 Length of feed capillary to balance point (L+L About mm 68 Total length of instrument (L cm 9.65

Head of liquid at the ball-point (at 45 inclination) About cm 1.4

In the unit 23 shown in FIGURE 6 a metal ball 24 is interposed between the follower 12c and the compression spring 140. In the normal writing attitude of the instrument, as shown, the ball 24 counteracts part of the positive head at the ball point (i.e., the point of balance indicated at C in FIGURE 1 is effectively lowered). However, when the unit 23 is inverted so that the nib 160 is uppermost, the ball 24 either partially or wholly compresses the spring 140 with the result that the negative head at the point C is reduced to a fraction of the value which would prevail were the ball not present. This reduces any tendency for the to run back from the ball point when the unit is in the inverted position.

In the construction shown in FIGURE 6 the follower 12c should be made slightly buoyant in the ink in order that it shall not sink into the ink when the ball 24 compresses spring 140.

The unit 25 shown in FIGURE 7 resembles in all material respects the units shown in FIGURES 1 to 4 except in that a secondary follower l2d is slidably disposed in the bore of the reservoir d beyond the follower 12d. The annular clearance between this secondary follower 12d and the bore of the reservoir is sealed with a sealing liquid having a viscosity of the order of 100 poise, so that, if the secondary follower 12'd is independent of the follower 12d, air or other gas is trapped in the space 26 between the two followers.

The follower -12d is shown as being of cylindrical form and it may incorporate a reservoir 27 for the sealing liquid comprising capillary slots or holes in the outer end of the follower substantially as described in our copending application for Reservoir Seal for Writing In strument, Serial No. 125,552, filed July 1961.

The secondary follower 12d acts as a viscous damper upon the liquid in the reservoir by virtue of the resistance to shear exhibited by its high viscosity sealing liquid combined with the resistance of the trapped air to change in volume. For this purpose the trapped air volume should be kept to a minimum by having a small gap of, say, 2 mm. between the two followers. This viscous damping effect is of importance if the reservoir liquid itself is of low viscosity, as for example in a fountain pen, since it prevents break up of the reservoir column when the unit is subjected to shock.

If the secondary follower 12d is made of high density material, e.g., copper or steel, it also operates substantially in the manner of ball 24 in FIGURE 6, for the gas or air trapped in space 26 functions like a spring connecting the two followers so that the elfect of the weight of follower 1221' is transmitted by this air spring to follower 12d. When the unit is held in the normal writing attitude, the heavy secondary follower 12'd tends to move downwards (causing a reduction in pressure of the trapped gas) but is elastically suspended from follower -12d by the trapped gas so that it operates to eifect a reduction of the positive head at the ball point in substantially the same manner as the ball 24. When the unit is inverted, the secondary follower lZ'd tends to slide down toward follower 12d, and therefore compresses the trapped gas. Its weight eifect is therefore transmitted by the trapped gas to follower 12d thereby wholly or partially counteracting the effect of spring 14d.

The capillary pressure diiferential across the ink meniscus remains unaltered despite variations of the pressure of the trapped air with varying angles of inclination. The pressure of the trapped air must of course remain within the limits laid down for such a liquid-sealed air space in our copending application, Serial No. 5,872.

In an alternative arrangement, illustrated in FIGURE 8, the secondary follower 12c is connected to the follower 12a which is in contact with the reservoir liquid, and the air space 26 is preferably vented to atmosphere via a hole 28 in the secondary follower. In this arrangement the shock-damping effect of the viscous sealing liquid around the secondary follower 12c is transmitted, by means of the connection, to the follower 122 which is in contact with the reservoir liquid. Under conditions of shock, the latter then behaves as if it were rigidly attached to the reservoir wall, and there is no danger of disturbing'the low viscosity reservoir liquid.

In all the instruments described herein the force exerted on the follower must normally, in all attitudes of the instrument, be insufficient to overcome completely the capillary forces in the narrow gap between the writing ball and its housing. If, however, after the follower has reached the upper limits of its travel, writing is continued, the positive head then prevailing may be adequate to overcome the capillary forces in the clearance around the follower so that the ink is withdrawn from that clearance, or the liquid seal around the follower is broken, and since air is then able to pass the follower, the latter is forced down by the spring. In certain cases it may then be possible to continue writing until the discharge duct 15 is empty, but the balanced condition described herein will, obviously, no longer exist.

Although the invention has been described herein with reference to specific embodiments, many modifications and variations therein will readily occur to those skilled in the art. Accordingly, all such variations and modifications are included within the intended scope of the invention as defined by the following claims.

We claim:

1. A liquid reservoir comprising a supply conduit having a bore open at one end to the exterior of the reservoir, a discharge duct leading from the other end of the bore to a dispensing extremity which is located farther from said other end of the bore than is the open end of the bore in a direction opposite to the direction from the open end of the bore to the other end of the bore, a piston slidable within the bore of the conduit having a crosssectional shape similar to but slightly smaller than that of the conduit bore to provide a clearance of capillary dimensions between the adjacent surfaces of the piston and the conduit, and means for urging the piston toward the open end of the conduit with increasing force as the piston moves away from the open end but with insuflicient force to drive the piston out of a liquid contained in the bore, thereby tending to compensate for the increase in liquid pressure at the dispensing extremity resulting from withdrawal of liquid from the reservoir when said extremity is below the piston in the conduit bore.

2. A liquid reservoir according to claim 1 wherein the discharge duct extends parallel to the conduit bore.

3. A liquid reservoir according to claim 1 wherein the means for urging the piston toward the open end of the conduit comprises a spring extending between the piston and a fixed point on the conduit.

4. A liquid reservoir according to claim 3 wherein the spring is a compression spring extending from the piston to the end of the conduit at which the conduit bore communicates with the discharge duct.

5. A liquid reservoir according to claim 3 wherein the change in spring orce per unit change in length of the spring is approximately equal to the change in force applied to the piston by a column of liquid in the conduit bore per unit change in length of the column.

6, A liquid reservoir according to claim 1 wherein the force applied by the urging means is suiiicient to produce a balance point in the discharge duct which is between the dispensing extremity and a point spaced from the junction of the discharge duct with the supply conduit by a distance equal to the length of the supply conduit.

7. A liquid reservoir according to claim 1 wherein the discharge duct extends axially through the bore and the piston has a central aperture through which the discharge duct passes.

8. A liquid reservoir according to claim 3 including a weight interposed between the spring and the piston.

9. A liquid reservoir according to claim 1 including a secondary follower slidable within the bore located between the first-mentioned piston and the open end of the bore, and a body of liquid surrounding the secondary follower and forming a seal between it and the conduit, thereby providing, in conjunction with the first-mentioned piston, a closed space to contain a trapped body of gas.

10. In combination, a liquid reservoir according to claim '1 wherein the discharge duct extends parallel to and along one side of the supply conduit and a holder comprising a shaft having an elongated central cavity to receive the supply conduit and having a longitudinal slot in its outer surface to receive the discharge duct.

11. A liquid reservoir comprising a supply conduit having a bore which is subject to atmospheric pressure at one end, a discharge duct leading from the other end of the bore to a dispensing extremity which is located farther from said other end of the bore than is said one end of the bore in a direction opposite to the direction from said one end or" the bore to the other end of the bore, a piston slidable within the bore of the conduit having a cross-sectional shape similar to but slightly smaller than that of the conduit bore to provide a clearance of capillary one end of the conduit with increasing force as the piston moves away from the said one end but with insufiicient force to drive the piston out of a liquid contained in the bore, thereby tending to compensate for the increase in liquid pressure at the dispensing extremity resulting from withdrawal of liquid from the reservoir when said extrernity is below the piston in the conduit bore.

12. A liquid reservoir comprising a supply conduit formed with a bore which is subject to atmospheric pressure at one end and forms a junction with a discharge duct at the other end, a discharge d-uct leading from the junction to a dispensing extremity, the distance between the dispensing extremity and the junction being greater than the distance between said one end and the junction and also greater than the distance between said one end and the dispensing extremity, a piston slidable within the bore of the conduit having a cross-sectional shape similar to but slightly smaller than that of the conduit bore to provide a clearance of capillary dimensions between the adjacent surfaces of the piston and the conduit bore, said piston being adapted to move at the end of a column of liquid in the bore in a direction from said one end toward the junction with the discharge duct, and means for urging the piston toward said one end of the conduit as the piston moves away from said one end but with insufficient force to drive the piston out of a liquid contained in the bore, thereby tending to compensate for the increase in liquid pressure at the dispensing extremity resulting from withdrawal of liquid from the reservoir when said extremity is at a lower level than the piston in the conduit bore.

References {Iited in the file of this patent UNITED STATES PATENTS 2,672,137 Fehling Mar. 16, 1954 FOREIGN PATENTS 158,350 Australia Aug. 19, 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 106. 190 October 8 1963 Hans Reinhard Fehling et all he above numbered pat- It is hereby certified that error appears in 0 Patent should read as ent requiring correction and that the said Letters corrected below.

Column 2, lines 6 and 7, for approximaterialy" read approximately column 4, line 51, for "throust" read thrust, column 10, line 37. for "2,672 137" read Signed and sealed this 7th day of April 1964.

SEAL) A Eowmm l BRENNER ERNEST W, SWIDER Attesting Officer Commissioner of Patents

Claims (1)

12. A LIQUID RESERVOIR COMPRISING A SUPPLY CONDUIT FORMED WITH A BORE WHICH IS SUBJECT TO ATMOSPHERIC PRESSURE AT ONE END AND FORMS A JUNCTION WITH A DISCHARGE DUCT AT THE OTHER END, A DISCHARGE DUCT LEADING FROM THE JUNCTION TO A DISPENSING EXTREMITY, THE DISTANCE BETWEEN THE DISPENSING EXTREMITY AND THE JUNCTION BEING GREATER THAN THE DISTANCE BETWEEN SAID ONE END AND THE JUNCTION AND ALSO GREATER THAN THE DISTANCE BETWEEN SAID ONE END AND THE DISPENSING EXTREMITY, A PISTON SLIDABLE WITHIN THE BORE OF THE CONDUIT HAVING A CROSS-SECTIONAL SHAPE SIMILAR TO BUT SLIGHTLY SMALLER THAN THAT OF THE CONDUIT BORE TO PROVIDE A CLEARANCE OF CAPILLARY DIMENSIONS BETWEEN THE ADJACENT SURFACES

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