GB2036333A - Fluid flow meter - Google Patents

Abstract

A flow meter, suitable for measurement of speed of water flowing in a stream, comprises a support member 13 rotatable against a biasing force by the force of flowing water acting on vanes 14, 15 carried by the support member. A first vane 14 is secured directly to the support member and a second vane 15 is mounted pivotally,on the member such that it can turn freely through a predetermined arc and only when this is exceeded does the vane bear on the support member. Preferably the second vane is more sensitive to the force of water flow than the first vane. The use of two vanes increases the sensitivity at low flow rates and extends the maximum flow rate that can be measured. The vane 15 may have a curved extension to increase its sensitivity. <IMAGE>

Description

SPECIFICATION Fluid flow meter This invention relates to a fluid flow meter and in particular, though not exclusively, to a flow meter suitable for measuring the speed of water flowing in a stream or channel.

It is a common disadvantage of many known kinds of fluid flow meters that they are either too expensive or too delicate for a particular use.

One common type of flow meter employs the well known venturi tube having a suitably shaped restriction or orifice in the flow path between the ends of the tube. A U-shaped tube of glass or transparent plastics is connected via flexible piping to two ports provided one either side of the restriction, and a difference of pressure at said ports results in a difference in level of fluid in the two limbs of the U-shaped tube. Though this type of meter is cheap and simple it is prone to damage. In use the U-shaped tube is readily bent or broken, or fluid in the U-tube is lost via the ends of the piping.

Another common type of flow meter comprises a rotatably mounted paddle wheel, and means such as a slipping clutch is utilised to obtain a reading related to the speed of rotation of the paddle wheel. In this type of flow meter the reading obtained is not very accurate unless a good quality slipping clutch is employed, and in this case the cost of the meter is increased significantly.

In accordance with the present invention I provide a flow meter comprising a rotatably mounted support member having two vanes attached thereto for positioning in a fluid flow path such that the force of fluid flowing against the vanes causes or tends to cause the support member to rotate about its rotational axis, a first of the vanes being secured to the support member so that the force of fluid flowing against said vane is transmitted directly to the support member to urge said member to rotate, the second vane being mounted for pivotal movement about said axis of rotation of the support member, and stop means whereby when said second vane is moved in at least a first direction by fluid flow said movement is transmitted to the support member.

Preferably the flow meter comprises biasing means, such as a torsion spring, which provides a resistance to movement of the support member proportional or otherwise related in a predetermined manner to the degree of movement undergone by the support member. Said biasing means preferably acts normally to bias the support member to a datum position.

Preferably the support member is in the form of a tube and said tube may be rotatably supported in a tubular casing. The vanes may be attached to the tube in the region of one end thereof, and display means may be attached or otherwise provided in the region of the other end of the tube.

Said tubular casing may house bearings for rotatably supporting the support member, and either directly or indirectly support the biasing means.

Preferably the display means comprises a pointer secured to and extending radially outward from one end of the support member tube. Said pointer may be arranged to move close to a calibrated scale provided on a display head. The display head may be secured to the tubular casing.

Alternatively, display means of other types may be employed. Thus, for example, the display means may comprise a digital counter connected either directly or via suitable gearing to the support member to give a reading related to the angular position of the support member.

Datum position stop means, comprising for example an abutment extending from an end of the tubular casing may be provided and arranged in conjunction with the biasing means such that normally the first vane and said abutment are urged into contact with one another by the biasing means, the positioning of said datum abutment determining in part the datum position on the calibrated scale.

Preferably the second vane is mounted for pivotal movement relative to the support member in such a manner that it may move angularly in both a clockwise and an anti-clockwise direction within a predetermined range of angular movement.

For the proper operation of the flow meter it is essential that the range of free angular movement of said second vane in at least one direction of rotation is less than 1800. Preferably the free angular movement is in the range 300 to 1200.

An angular range of 900 is believed to be particularly suitable.

It is further preferred that one extremity of said range of angular movement coincides substantially with the angular position at which the first vane is fixed relative to the support member.

One of the limits of the range of free angular movement may coincide exactly with the angular position of the first vane, or may be slightly offset to one side thereof, e.g. in the range 10 to 200 to one side, such that the angular range of movement is a little less than the minimum angle between the other limit of free movement and the position of the fixed vane.

In an alternative embodiment the second vane may be mounted relative to the support member by means of a ratchet or like means which permits free angular movement of the second vane relative to the support member in one direction through at least part of a revolution but restrains relative angular movement in the opposite direction.

Notwithstanding the aforedescribed constraints on the angular movements of the first and second vanes relative to the support member, one or both of the vanes may be hingedly or otherwise attached to the support member so that when not in use they may be folded about an axis substantially perpendicular to the rotational axis of the support member so as to lie compactly alongside the support member, or alternatively be removed for storage.

In addition to the said first and second vanes, one or more additional vanes may be provided and may be of a fixed and/or pivotally mounted form.

The vanes may be of similar or different size and/or shape. Preferably the moment of area of the second vane about the rotation axis of the support member is greater than that of the first vane. The vanes may be mounted on the support means in side-by-side manner but particularly where a compact construction is sought, two or more vanes may be mounted in an overlapping configuration.

To facilitate measurement of a wide range of flow rates, vanes of different sizes may be provided, and display means may be calibrated with scales related to the different vane sizes or interchangeable scales may be provided.

Retention means, such as a spring-loaded bar hingedly mounted relative to the support means, may be provided for ease of interchange of the vanes.

The measurement of a wide range of flow rates may be facilitated alternatively by a vane extension, such as a curved fin, selectively attachable to and removable from a vane.

Damping means may be provided to dampen the movement of the support member relative to the casing and thus the calibrated scale, such that a steady reading related to flow rate is obtained without undue delay.

Particularly where the flow meter is to be used for measuring a direction of flow, e.g. of sea or river underwater currents, the meter may be provided with a compass.

For protection against accidental damage the vanes may be provided with a cage or like protective member which does not significantly affect the fluid flow rate in the vicinity of the vanes but assists to prevent them being impacted with debris carried in the fluid flow.

Particularly if the flow meter is to be used for measuring flow in a stream or other area of shallow water a foot support may be provided below the vanes such that they are maintained clear of the bed of the stream, or like boundary of a fluid flow channel, and are free to move angularly clear of said bed.

Especially if the flow meter is to be used for measuring flow in a channel, pipe or other fluid flow path of known cross-sectional area, the display means may be calibrated in relation to volume flow instead of speed. Several volume flow rate scales may be provided on the display means, each being appropriate to a particular cross-sectional area of fluid flow path of depth of fluid in a channel of known cross-section.

If the flow meter is to be used for measuring flow rates and/or indicating flow directions at different depths, a calibrated depth scale may be provided, e.g. on the tubular casing.

Several embodiments of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings in which Figure 1 shows a perspective view of a flow meter in accordance with the present invention; Figure 2 shows part in cross-section a side elevation of part of the flow meter shown in Figure 1; Figure 3 is a detail in perspective of one of the vanes shown in Figures 1 and 2; Figure 4 is a section on a line 4 4 of Figure 2; Figure 5 shows in perspective an alternative vane assembly; Figure 6 is a cross-section on the line 6 - 6 of Figure 5; Figures 7 and 8 each show in perspective further vane details; Figure 9 shows a side view of yet another vane assembly, and Figure 10 is a section on the line 10-10 of Figure 9.

A flow meter 10 suitable for measuring the flow rate of water in a stream comprises a tubular casing 11 formed from a one metre length of 30mm bore p.v.c. plastics tube.

A nylon bearing piece 12 is provided in the bore of the casing, in the region of an enlarged end thereof. A vane support member comprising a tubular rod 13 of stainless steel or other noncorrosive metal is rotatably supported by said bearing and extends beyond both ends of casing 11. End stops 27 are secured to the rod 1 3 to resist movement thereof relative to the casing. Drain holes 28 allow water to drain from the casing.

That end, a lower end, of the support rod 13 in the region of the bearing piece 12 carries two brass vanes 14, 1 5 the mounting of which will be described in more detail below. The other end of the support rod has attached thereto a pointer 1 6 which extends radially outwards from the rod in a direction perpendicular to the length of the rod.

The pointer 16 is disposed such that when rotated it moves over a calibrated scale marked on the surface of a moulded plastic disc 17 affixed to a dial housing 18 at an end of the casing 11. A compass 29 is positioned in the dial housing and is rotatable by means of a knurled pin 30.

The dial housing 1 8 and bearing piece 1 2 serve also as abutments for the end stops 27. The dial housing further serves to position the upper end of rod 13.

Datum position stop means comprising an abutment 1 9 extending downwards from an end of the casing 11 limits angular movement of the fixed vane and thus also the support rod 1 3 relative to the casing in a first angular direction. A spiral torsion spring 20 is secured at its ends respectively to the dial housing 1 8 and rod 13 and serves normally to retain the fixed vane 14 in contact with the abutment 1 9.

One of the vanes, vane 14, is secured rigidly to the support rod 13 so that forces tending to rotate the vane either clockwise or anti-clockwise relative to the support rod 13 are transmitted directly to said rod.

The second vane, vane 15, is pivotally mounted such that it is free to move-angularly relative to the support rod 13 about the axis of rotation of the support rod, between two position which subtend an angle of 900 at the support rod.

In this embodiment of the invention, the fixed vane 14 has a cross-sectional area half that of the vane 15.

The construction of the second vane 1 5 is shown in greater detail in Figure 3. One edge region of the flat portion of vane 1 5 is brazed to a tubular sleeve 22 and a rectangular window 23 is formed in said sleeve.

In the assembled construction of the vane 1 5 and support rod 13, the rod extends through said sleeve 22, and a stud 24 (see Figure 2) secured to the rod 1 3 protrudes radially outwards therefrom through said window 23. The diameter of the stud 24 and the spacing of those edges 25,26 of the window extending parallel with the sleeve 22 are selected such that the vane 1 5 can rotate freely through an angle of 900 as the stud moves from contact with one edge into contact with the other edge. The stud 24 thus co-operates with said edge 26 to act as stop means whereby when said second vane is moved in a clockwise direction said movement is transmitted to the rod 1 3.

The fixed vane 14 is typically mounted on the rod 1 3 to lie at approximately 900 relative to the pointer in a clockwise direction as looking down on disc 17. The vane 15 is mounted such that the 900 angle through which it can move freely lies between two limits iying respectively at 0 and 900 relative to the position of the fixed vane as considered in said clockwise direction, i.e. in a direction opposite the direction of the torque exerted by the spring 20 on the support rod 13.

In use of the flow meter, before the vanes are positioned in a flow of fluid, the pointer 16 will lie at a datum position relative to the calibrated scale determined by the relative angular position of the pointer 1 6 and the abutment 19 against which the vane 14 is urged by the spring 20.

The second vane 1 5 is moved to lie at 900 relative to the fixed vane and the flow meter is then lowered into the flow of water with the fixed vane 14 pointing upstream, that is, against and parallel with the direction of fluid flow.

Initially the force of water will act on the vane 1 5 to move it to a position dependent on the flow rate, said movement causing rotation of the rod 13 and fixed vane 14 which will then become angled to the flow direction and acted on by the force of the flow water.

If the force of the water on the vanes 14, 1 5 is sufficiently great the vane 15 will move to lie parallel with the fluid flow direction, pointing, downstream, and the fixed vane will correspondingly lie substantially at right angles to the direction of fluid flow.

Any additional force in the water flow will then act only on the fixed vane 14 to move it through up to a further 900 to lie substantially parallel with the fluid flow direction, pointing downstream. In this position it would then lie almost parallel with the second vane 1 5 which, by virtue of its ability to move freely through 90 relative to the support rod, has been able to remain aligned with the fluid flow direction during said further 900 of movement of the fixed vane.

From the foregoing it will be appreciated that because of the initial disposition of the second vane 1 5 to lie substantially at right angles to the direction of fluid flow it has a sensitivity to the force of the water flow greater than that of a vane lying at any other angle. At medium flow rates both vanes are acted on by the flow rate so that although neither lies at right angles to the direction of fluid flow there is a good sensitivity and thus accuracy in detection of the flow rate. At higher flow rates the sensitivity of the meter is not so good but because only one vane is subject to the force of the water flow, flow rates significantly greater than those at mid range of the calibrated scale can be measured.

By employing two vanes in the manner described the pointer can move through substantially 1 800 over a calibrated scale without the provision of toothed gears and particularly at low flow rates thereby provide a better sensitivity than would a similar flow meter provided with only a single vane.

In a modified form of the above described embodiment the second vane, vane 1 5 is mounted such that the 900 angle through which it can move freely lies between two limits respectively at 100 and 100 relative to the position of the fixed vane as considered in a direction opposite that of the torque exerted by the spring 20 on the support rod 1 3. (See Figure 4.) Thus, when the flow meter is lowered into a fluid flow path it is not essential first to position the second vane to lie at an angle, e.g. 900 relative to the flow direction.With the fixed vane 14 initially pointing against the direction of fluid flow the offset of the second vane will cause the fluid flow pressure to swing the second vane to lie at a position 1000 relative to the fixed vane with the stud 24 then in contact with edge 26. Further movement of the second vane, and also the first vane, is then dependent on the fluid flow rate.

In this construction it will be appreciated that the fixed vane can move through only 1700 before the second vane is urged beyond the downstream position and into the path of oncoming fluid. The useful movement of pointer 1 6 is thereby reduced.

In a second embodiment of the invention a flow meter is constructed substantially as described with reference to Figures 1 to 3 except that the vanes are of a different construction as illustrated in Figures 5 and 6. A fixed vane 50 and hinged vane 51 are mounted in an overlapping manner on a support rod 52. The vane 50 is formed with a curved portion 53 close to the support rod such that the vane 51 may lie alongside the fixed vane 50 in a compact manner. The vane 51 is provided with a cut out recess portion 54 to accommodate said curved portion 53 of the hinged vane. In this construction the aforedescribed datum abutment is spaced from the fixed vane by the second vane.

Therefore the support rod 52 is provided with a pin 55 which normally is urged against the abutment to define the datum position.

In a third embodiment of the invention a flow meter again constructed substantially as described with reference to Figures 1 to 3 comprises a pivotally mounted vane 70 (see Figure 7). The vane 70 is provided with a quadrant portion 71 which lies in the plane of rotation of the support rod and said quadrant portion supports a shoulder 72 which extends perpendicular to the plane of the vane face 73, thereby to act as a stop member engageable with a fixed vane thereby to limit pivotal movement of vane 70 in a first direction.

In Figure 8 there is shown a vane 80 to which a curved fin 81 of moulded plastics is secured by metal spring clips 82. The fin increases the sensitivity of the vane to fluid flow and gives a greater accuracy in the measurement in particular of low flow rates. Fins may be affixed selectively to one or more of the vanes of a flow meter in accordance with the present invention.

In Figures 9 and 10 there is shown a further vane assembly comprising a fixed vane 90 and a pivotally mounted vane 91. Each vane extends from a tubular sleeve 93 by which it is mounted on a rotatable support member 94, and relative movement of the vane 91 with respect to the support member 94 is restricted by stop means comprising cogs 95, 96 formed at the ends of the sleeves of vanes 90,91 respectively Cog 95 has a 1 800 segmental recess and cog 96 has a 2700 segmental recess thereby restricting relative angular movement to 900.

Whilst the invention has been described specifically in relation to a portable flow meter, it will be appreciated that flow meters may be incorporated into a pipework or channel system as a permanent installation.

Claims (22)

1. A flow meter comprises a rotatably mounted support member having two vanes attached thereto for positioning in a fluid flow path such that the force of fluid flowing against the vanes causes or tends to cause the support member to rotate about its rotational axis, a first of the vanes being securing to the support member so that the force of fluid flowing against said vane is transmitted directly to the support memberto urge said member to rotate, the second vane being mounted for pivotal movement about said axis of rotation of the support member, and stop means whereby when said second vane is moved in at least a first direction by fluid flow said movement is transmitted to the support member.

2. A flow meter according to claim 1 and comprising biasing means to provide a resistance to movement of the support member related in a predetermined manner to the degree of movement undergone by the support member.

3. A flow meter according to claim 2 wherein said biasing means comprises a torsion spring.

4. A flow meter according to claim 2 or claim 3 wherein said biasing means acts normally to bias the support member to a datum position.

5. A flow meter according to any one of the preceding claims wherein the second vane is free to pivot both clockwise and anti-clockwise relative to the support member within a predetermined range of angular movement.

6. A flow meter according to claim 5 wherein said range of free angular movement is less than 1800.

7. A flow meter according to claim 6 wherein said range of free angular movement is greater than 300 and less than 1200.

8. A flow meter according to claim 6 wherein said range of free angular movement is 900.

9. A flow meter according to any one of claims 5 to 8 wherein the positions of the first and second vanes coincide substantially when the second vane is at an extremity of the range of free pivotal movement thereof relative to the support member.

10. A flow meter according to claim 9 wherein said extremity position is offset slightly relative to the position at which the first vane is fixed relative to the support member.

11. A flow meter according to claim 10 wherein said offset is in the range 100 to 200..

12. A flow meter according to any one of claims 1 to 4 and comprising means to permit free angular movement of the second vane relative to the support member in one direction through at least part of a revolution but restrain relative angular movement in the opposite direction.

13. A flow meter according to any one of the preceding claims wherein the moment of area of the second vane about the rotational axis of the support member is greater than that of the first vane.

14. A flow meter according to any one of the preceding claims wherein the vanes are mounted in an overlapping configuration.

15. A flow meter according to any one of the preceding claims wherein the size of a vane may be varied selectively.

1 6. A flow meter according to claim 1 5 wherein a vane is releasably secured to the support member.

1 7. A flow meter according to claim 1 5 wherein a vane is provided with a selectively removable vane extension.

18. A flow meter according to claim 17 wherein the vane extension is in the form of a curved fin.

19. A flow meter according to any one of the preceding claims wherein a vane is hingedly attached to the support member thereby to permit the vane to be folded about an axis substantially perpendicular to the rotational axis of the support member.

20. A flow meter according to any one of the preceding claims incorporating a protective cage for the vanes.

21. A flow meter according to any one of the preceding claims wherein a foot support is provided to maintain the vanes clear of the boundary of a fluid flow channel.

22. A flow meter constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.