GB2063428A

GB2063428A - Needle Valve

Info

Publication number: GB2063428A
Application number: GB8037055A
Authority: GB
Original assignee: Blatchford & Sons Ltd
Current assignee: Blatchford & Sons Ltd
Priority date: 1979-11-20
Filing date: 1980-11-19
Publication date: 1981-06-03
Also published as: GB2063428B

Abstract

In a metering valve, a valve member has a needle portion (7) positioned in the opening to a fluid- carrying tube (5). The needle portion (7) is non-linearly tapered so that the area of the orifice formed at the tube opening is logarithmically related to the axial position of the needle member. Axial adjustment of the valve member is effected by means of a knob (not shown) rotatably mounted on a threaded portion (8) of the valve member. The valve member may have a cut out, as shown, have a profiled circular cross-section over its operative length, Fig. 5, (not shown), be cylindrical and hollow and have operatives of progressively increasing diameter communicating with the hollow interior, Fig. 4, (not shown) or the seat may be flared. The valves are used in a piston and cylinder unit for a knee joint (Fig. 1, not shown) to provide adjustable resistance to movement. <IMAGE>

Description

SPECIFICATION Needle Valve This invention relates to an adjustable needle valve, and in particular for example to a needle valve which is manually adjustable to a plurality of settings to regulate fluid flow.

The needle valve is a well-known valve configuration which is frequently used when it is required to control accurately and consistently a relatively small fluid flow in a fluid-carrying passage. The known valve comprises a tapered needle of circular cross-section mounted coaxially in the open end of a tube or in a circular aperture, the needle being movable in an axial direction relative to the tube end to vary the cross-sectional area of the space between the needle and the tube. In general, the tapered needle is conical in form over much of its length so that the area of the orifice formed between the needle and the tube end varies as a function of the square of the distance by which the needle is inserted into the tube.If the insertion distance is considered in terms of a series of incremental adjustments, for example the number of turns of an adjustment screw, the percentage increase in orifice area for each successive increment as the needle is withdrawn varies widely, starting from infinity for the first increment and decreasing steadily as the valve is opened. This means that adjustment of the resistance to fluid flow through the valve is coarse for small orifice areas but relatively fine as the needle approaches the fully withdrawn position. It is an object of this invention to provide a valve which at least reduces this variation in adjustment sensitivity.

According to this invention a needle valve comprises a needle member mounted in an opening communicating with a fluid-carrying passage, the needle member being positionally adjustable in an axial direction to form one or more orifices having a total cross-sectional area which is logarithmically related to the axial position of the needle member with respect to the opening.

The invention is particularly applicable to the control of fluid flow in a piston and cylinder device, as used for example in an artificial limb for controlling the rate of flexion and extension of the knee joint. Therefore, according to another aspect of the invention there is provided a control unit for regulating rotation of the knee joint in an artificial leg, the unit comprising a piston movable inside a closed cylinder, one end of the cylinder communicating with a needle valve having a needle member which is adjustable in position, the area of the orifice defined by the needle member being logarithmically related to the axial position of the needle member. The valve may be positioned in a by-pass passage connecting opposite ends of the cylinder, thereby regulating the movement of the piston in both directions.In a preferred embodiment of the control unit opposite ends of the cylinder are connected by two by-pass passages, each containing an adjustable needle valve, one of the passages also including a non-return valve so that the resistance to piston motion is greater in one direction than in the other. The preferred embodiment is a pneumatic device, and is a development of a pneumatic control device which is known in the artificial limb field. However, it should be understood that the invention is also appiicable to hydraulic devices.

The advantage of using a valve or valves with a logarithmic resistance characteristic in an artificial limb control unit is that the user can adjust the or each valve in a series of fixed steps determined for example by "click" stops knowing that each step will produce a single, largely fixed, percentage increase or decrease in resistance over substantially the whole adjustment range of the valve. This can simplify and shorten the setting-up procedure, especially in the case of a unit having two such valves. It also allows a valve having the required range and sensitivity of adjustment to be made relatively compact, in that the needle can be relatively short.

The invention will now be described by way of example with reference to the drawings in which Figure 1 is a partly sectioned side view of a control unit in accordance with the invention; Figure 2 is an enlarged view of the needle valve visible in Figure 1; Figure 3 is an enlarged cross-section on the line X-X of the needle member in Figure 2; Figure 4 shows part of a first alternative embodiment of needle member; and Figure 5 shows a second alternative embodiment of needle member.

Referring to Figure 1, a pneumatic control unit has a cylinder 1 supported between two end housings 2 and 3, and a piston (not shown) linked to a piston rod 4. The interior of the cylinder communicates via drillings in the housings with by-pass tubes 5 and 6, which serve to connect the air space behind the piston with the air space in front of the piston. Each by-passing passage so formed includes an adjustable needle valve having a needle member with a needle portion 7 and a coaxial threaded portion 8, the latter portion being received in a rotatable adjustment knob 9.

The needle member (shown more clearly in Figure 2) is prevented from rotating by flats on the threaded portion 8 so that rotation of the knob causes the needle portion 7 to move into or out of the end portion of the tube 5.

A feature of the control unit which is not shown in Figure 1 is a non-return valve situated in the housing 3 to restrict flow in the tube 6 to one direction only so as to provide for differential resistance settings in the two directions of movement of the piston. Normally, for a control unit intended to be mounted in an artificial leg, the non-return valve is arranged to allow air flow through the tube 6 from left to right in Figure 1, i.e. on the piston outstroke, and to prevent flow in the opposite direction. This gives a greater resistance to flexion of the knee joint compared to the resistance to extension.

The needle member of Figures 1 and 2 has a needle portion 7 tapered as shown to achieve the required logarithmic characteristic. Over substantially the whole of its length, the needle portion 7 has a cross-section in the form of a disc with a segment 10 removed, as shown in Figure 3. The size of the removed segment 10 varies non-linearly along the length of the portion 7, from a very small segment near the root to well over 50% of the area of the circle adjacent the tip.

At any cross-section along the length of the needle portion 7, the removed segment 10 is defined by a chord 11 which is parallel to a fixed imaginary plane 12 containing the longitudinal axis of the needle portion. In other words the orientation of the chord 11 is constant with respect to the needle portion. The portion 7 is axially movable in an end portion of the tube 5, which portion has an accurately machined bore 13 to match the fully diameter of the portion 7.

The dimensions of the extreme left-hand end of the bore in particular are closely controlled since it is at this point that the orifice (shaped as at 11 in Figure 3) is formed between the needle portion and the tube. The profile of the upper surface as seen in Figure 2 of the needle portion 7 is such that each clockwise turn of the knob 9 produces a fixed percentage increase in the orifice area. In a preferred embodiment the percentage is 35% over virtually the whole range of adjustment.

(Clearly, the first turn from the fully closed position will not ahere to this percentage). In fact, the orifice area increases as a function of k', where k is a constant and I is the distance by which the needle portion has been withdrawn from the tube, and therefore a straight line graph results when the log of the orifice area, logkA, is plotted against I.

To simplify machining of the needle portion, the upper surface profile can be considered as being composed of two or more arcs of different radii. The particular example shown in Figure 2 was profiled to the combination of a straight line adjacent the root, followed by a relatively large radius arc centered on a vertical line passing through the root, followed in the region of the tip by a relatively small radius arc centered on the lower edge of the needle portion.

The general method described above of profiling the needle portion in one diameter only is the preferred method of construction since it allows a profile of adequate accuracy to be produced relative cheaply. Needle members produced by alternative methods are shown in Figures 4 and 5.

Figure 4 shows a "piccolo" valve needle having 10 transverse, longitudinally spaced holes (i) to (x) of varying size to produce a valve with the required logarithmic characteristic. Each hole opens into a central bore 14 which communicates with the interior of the tube 5. As the needle is withdrawn from its closed position, holes of progressively increasing diameter are uncovered successively. The total orifice area increases stepwise and approximates to the required exponential characteristic. This method of construction is relatively cheap but does not correspond to required characteristic so accurately as the profiled version described above.

A further alternative is shown in Figure 5, this being a valve needle having a circular cross section over its whole operative length 13. The diameter of the needle varies exponentially along the length 15, but the variations in diameter are much smaller than in the "single diameter profiled" version. Consequently, this embodiment necessitates extremely accurate, and therefore expensive, machining.

Yet a further alternative embodiment has a valve needle with a uniform or flared circular cross-section over its operative length, the needle being movable within a tapered (e.g. trumpetshaped) bore to produce the required logarithmic characteristic.

Claims

1. A needle valve comprising a needle member mounted in an opening communicating with a fluid-carrying passage, the needle member being positionally adjustable in an axial direction to form one or more orifices having a total cross-sectional area which is logarithmically related to the axial position of the needle member with respect to the opening.

2. A valve according to claim 1 wherein, the logarithmic relationship is such that successive, equal incremental adjustments of the axial position of the needle member produce corresponding, substantially equal percentage changes in the total orifice area.

3. A valve according to claim 1 or claim 2 wherein the needle member has a needle portion, an end part of which portion is tapered nonlinearly to provide the logarithmic relationship between the orifice area and the needle member position.

4. A valve according to claim 3, wherein the fluid carrying passage terminates at the said opening, and the needle portion is positioned inside the passage.

5. A valve according to claim 4 wherein the opening is circular in cross-section: and the needle portion, over at least part of its length, has a cross-section in the shape of a disc with a segment removed so as to produce an orifice at the opening which is in the form of a segment of a circle; the removed segment being defined by a chord, the position of which chord relative to the longitudinal axis of the needle portion varies along the length or part of the length of the needle portion so that the area of the segmental orifice increases as the portion is progressively withdrawn from the passage.

6. A valve according to claim 5 wherein for any cross-section of the needle portion in the said length or the part of the said length the chord is parallel to a reference plane containing the longitudinal axis of the needle portion, the plane being fixed relative to the needle member.

7. A valve according to claim 1 or claim 2 wherein: the opening is circular in cross-section; and the needle member includes a substantially cylindrical needle portion positioned in the opening and having a central longitudinal bore which connects the fluid-carrying passage with a plurality of orifices in the needle portion, the orifices comprising a plurality of transverse, longitudinally spaced holes between the outer surface of the needle portion and the central bore.

8. A valve according to any of claims 3 to 7 wherein the needle member comprises the needle portion and a coaxial threaded portion for rotational adjustment of the longitudinal position of the needle portion relative to the opening.

9. A valve according to claim 8 wherein the needle member is shaped to prevent rotation of the member in the opening, and wherein a rotatable adjustment knob is mounted on the threaded portion.

10. A valve according to claim 1 or claim 2, wherein the needle member has a needle portion of uniform or flared cross-section, the end of the needle portion being positioned inside the passage, and the passage having a tapered bore.

1 A piston and cylinder control device for an artificial limb, including a valve according to any preceding claim.

12. A control device according to claim 11 in which the cylinder space on one side of the piston communicates with the cylinder space on the other side of the piston via a by-pass passage including a needle valve according to any of claims 1 to 10.

1 3. A control device according to claim 12 wherein the by-pass passage includes a nonreturn valve.

14. An artificial limb including a control device according to any of claims 11 to 13.

1 5. A needle valve constructed and arranged substantially as herein described and shown in the accompanying drawings.