GB2090419A - Zero adjustment of flowmeters - Google Patents

Abstract

The movable member (19) of a variable area flowmeter is coupled to a pointer by a bar magnet (21) in a bore (22) of the member and a circular magnet (32). To permit zero adjustment of the pointer the position of the bar magnet is adjustable by means of a screw (24). Access to the adjusting means is through the inlet or outlet ports (45), (46). <IMAGE>

Description

SPECIFICATION Flowmeter This invention relates to flowmeters of the type comprising a body, an inlet leading to the smaller diameter end of a tapered passage in the body leading to an outlet, an annular seating at the smaller end of the tapered passage and facing towards the larger end, a circular valve member, a spring urging the valve member towards contact with the seating, a plunger co-axial with the valve member and slidable in a bore in the body, at least one bar magnet housed in the plunger, a pointer pivoted on the body, and a scale over which the pointer is moved by the magnet and which is calibrated in accordance with the flow of fluid through the tapered passage for corresponding positions of the valve member spaced from the seating.There is therefore no mechanical link between the valve member and the pointer, and so this type of flowmeter is particularly suitable for highpressure fluids.

Such a flowmeter is described in U.K. Patent Specification 1 201 441 and corresponding U.S.

Patent Specification 3 626 756 as having a pair of bar magnets end-to-end in the plunger with the adjacent poles of like polarity but spaced from each other, the pointer being made of ferromagnetic material and being disposed transversely of the barrel so as to be constrained by the like adjacent poles to move over the scale in accordance with movement of the plunger and magnets with the valve member. The disadvantages of this arrangement is that, when the bar magnets have been fitted inside the plunger and the plunger has been fitted inside the barrel, there is no way in which the positions of the bar magnets inside the plunger can be adjusted to allow for manufacturing tolerances and set the pointer against the zero of the scale.It is possible to provide for adjustment of the scale along the body to bring the zero of the scale into register with the pointer when there is no flow through the meter, but this method of "zero-ing" the pointer is likely to upset the calibration of the scale. Thus the scale of each flowmeter has to be calibrated individually for real accuracy of all rates of flow.

The object of the invention is to provide a flowmeter of the type initially described with means whereby the pointer can be "zero-ed" without upsetting the calibration of the scale.

According to the present invention, a flowmeter comprises a body, an inlet leading to the smaller diameter end of a tapered passage in the body leading to an outlet, an annular seating at the smaller end of the tapered passage and facing towards the larger end, a circular valve member, a spring urging the valve member towards contact with the seating, a plunger coaxial with the valve member and slidable in a bore in the body, at least one bar magnet slidable in a coaxial bore in the plunger, a screwthread in the bore in the plunger, a screw mating with the screwthread and adjustable therealong for adjusting the position of the magnet along the bore in the plunger, a pointer pivoted on the body, and a scale over which the pointer is moved by the magnet and which is calibrated in accordance with the flow of fluid through the tapered passage for corresponding positions of the valve member spaced from the seating.

The bar magnet (or magnets) may be attached to the screw, or the bar magnet (or magnets) may be urged towards the screw by a coil spring compressed between the magnet (or magnets) and a blind end of the bore in the plunger. The adjusting screw may be accessible through an end of the bore in the plunger opening through the centre of the valve member, or through an end of the bore in the plunger opening remote from the valve member, and the open end of the bore in the plunger may be sealed by a plug after adjustment of the position of the magnet (or magnets) has been effected.

Although a pair of bar magnets may be provided in the plunger, as described previously with reference to U.K. Patent Specification 1201441 and corresponding U.S. Patent Specification 3626756, with a ferromagnetic pointer, it is convenient to use only one bar magnet in association with a circular magnet having diametrically opposed poles and secured to the pointer for movement about an axis perpendiculay to the axis of the plunger and laterally offset therefrom, whereby the scale may be marked out over 180 or a substantial part thereof. The circular magnet may be disc-like (i.e., a thin annulus) or it may be cylindrical, in either case being mounted in a cross-bore in the body and on a non-magnetic spindle carrying the pointer externally of the body.

The inlet and outlet are preferably coaxial with the valve member and plunger and are preferably provided in respective end caps bolted to respective ends of the body, with longitudinal (non-axial) bores through the body from the larger end of the tapered passage to the outlet. The inlet end cap preferably has a tubular spigot sealed in an enlargement of a counterbore of the axial bore in which the plunger slides, the enlargement of the counterbore also housing a cylindrical insert in which is provided the tapered passage, which insert is replaceable or interchangeable. The spigot of the inlet end cap conveniently also provides the seating round the inlet. The outlet end cap preferably has a tubular spigot sealed in a chamber in the body into which the longitudinal (non-axial) bores discharge and which may also be a counterbore of the axial bore in which the plunger slides.The end caps are preferably provided with screwthreaded counterbores to enable the flowmeter to be connected in a pipeline.

A preferred embodiment of the invention and two possible modifications will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of the preferred embodiment of flowmeter in accordance with the invention; Figure 2 is an end elevation of the flowmeter of Figure 1; Figure3 is a longitudinal section of the flowmeter taken on the line Ill - Ill of Figure 2; Figure 4 is a side elevation of the flowmeter partially in section generally on the line IV - IV of Figure 3; Figure 5is a fragmentary cross-section taken on the line V - V of Figure 3; and Figures 6 and 7 are longitudinal sections similar to Figure 3 but showing modifications in plunger construction.

The flowmeter shown in Figures 1 to 5 comprises a body 10, an inlet 11 leading to the smaller diameter end 12 of a tapered passage 13 in the body leading to an outlet 14, an annular seating 15 at the smaller end of the tapered passage and facing towards the larger end 16, a circular valve member 17, a spring 18 urging the valve member towards contact with the seating, the plunger 19 coaxial with the valve member and slidable in a bore 20 in the body, a bar magnet 21 slidable in a coaxial bore 22 in the plunger, a screwthread 23 in the bore 22, a screw 24 mating with the screwthread and adjustable therealong for adjusting the position of the magnet along the bore 22, a pointer 25 pivoted on the body, and a scale 26 over which the pointer is moved by the magnet and which is calibrated in accordance with the flow of fluid through the tapered passage 13 for corresponding positions of the valve member 17 spaced from the seating 15.

The bar magnet 21 is attached to the screw 24, but alternatively, as shown in Figures 6 and 7, the bar magnet 21 may be urged towards the screw 24 by a coil compression spring 27 compressed between the magnet and a blind end 28 of the bore 22 in the plunger 19. The adjusting screw 24 in Figures 3 and 6 is accessible through an end of the bore 22 opening remote from the valve member 17, while in Figure 7 the adjusting screw is accessible through an end of the bore 22 opening through the centre of the valve member 17; and the open end of the bore 22 in the latter case is sealed by a plug 29 after adjustment of the position of the magnet 21 has been affected. In the modification of Figure 6, the valve member 17 is formed separately from the plunger 19 and has a spigot 30 secured in a separate blind bore 31 in the plunger 19 by a pin 32.

The bar magnet 21 is used in association with a circular magnet 32 having diametrically opposed poles and secured to the pointer 25 through a non-magnetic spindle 33 (mounted in bearings 34 in an insert 35 in the body 10) on an axis perpendicular to the axis of the plunger 19 and laterally offset therefrom, whereby the scale 26 may be marked out over 180 of a substantial part thereof.

The inlet 11 and the outlet 14 are coaxial with the valve member 17 and plunger 19 and are provided in respective end caps 36, 37 bolted to respective ends of the body 10, with longitudinal (non-axial) bores 38 through the body from the larger end 16 of the tapered passage 13 to the outlet. The inlet end cap 36 has a tubular spigot 39 sealed in an enlargement 40 of a counterbore 41 of the axial bore 20 in which the plunger 19 slides, the enlargement 40 of the counterbore 41 also housing a cylindrical insert 42 in which is provided the tapered passage 13, which insert 42 is interchangeable. The spigot 39 of the inlet end cap 36 also provides the seating 15 round the inlet 11.

The outlet end cap 37 has a tubular spigot 43 sealed in a chamber 44 in the body 10 into which the longitudinal (non-axial) bores 38 discharge and which may also be a counterbore of the swivel bore 20 in which the plunger slides, as in the case in Figures 3 and 6. The end caps 36,37 are provided with screwthreaded counterbores 45,46 to enable theflowmeterto be connected in a pipeline.

A cover 47 with a window 48 is provided for the pointer 25 and scale 26.

Claims (16)

1. A flowmeter comprising a body, an inlet leading to the smaller diameter end of a tapered passage in the body leading to an outlet, an annular seating at the smaller end of the tapered passage and facing towards the larger end, a circular valve member, a spring urging the valve member towards contact with the seating, a plunger coaxial with the valve member and slidable in a bore in the body, at least one bar magnet slidable in a coaxial bore in the plunger, a screwthread in the bore in the plunger, a screw mating with the screwthread and adjustable therealong for adjusting the position of the magnet along the bore in the plunger, a pointer pivoted on the body, and a scale over which the pointer is moved by the magnet and which is calibrated in accordance with the flow of fluid through the tapered passage for corresponding positions of the valve member spaced from the seating.

2. Aflowmeter as in Claim 1, wherein the bar magnet is attached to the screw.

3. A flowmeter as in Cliam 1, wherein the bar magnet is urged towards the screw by a coil spring compressed between the magnet and a blind end of the bore in the plunger.

4. A flowmeter as in any one of Claims 1 to 3, wherein the adjusting screw is accessible through an end of the bore in the plunger opening through the centre of the valve member.

5. A flowmeter as in any one of Claims 1 to 3, wherein the adjusting screw is accessible through an end of the bore in the plunger opening remote from the valve member.

6. Aflowmeter as in Claim 4 or Claim 5, wherein the open end of the bore in the plunger is sealed by a plug after adjustment of the position of the magnet has been effected.

7. A flowmeter as in any one of Claims 1 to 6, wherein a single bar magnet is used in association with a circular magnet having diametrically opposed poles and secured to the pointer for movement about an axis perpendicular to the axis of the plunger and laterally offset therefrom.

8. A flowmeter as in Claim 7, wherein the circular magnet is disc-like.

9. A flowmeter as in any one of Claims 1 to 8, wherein the inlet and the outlet are coaxial with the valve member and plunger.

10. A flowmeter as in Claim 9, wherein the inlet and the outlet are provided in respective end caps bolted to respective ends of the body, with longitudinal bores through the body from the larger end of the tapered passage to the outlet.

11. A flowmeter as in Claim 10, wherein the inlet end cap has a tubular spigot sealed in an enlarge ment of a counterbore of the axial bore in which the plunger slides, the enlargement of the counterbore also housing a cylindrical insert in which is provided the tapered passage, which insert is replaceable or interchangeable.

12. A flowmeter as in Claim 11, wherein the spigot of the inlet end cap provides the seating round the inlet.

13. A flowmeter as in any one of Claims 10 to 12, wherein the outlet end cap has a tubular spigot sealed in a chamber in the body into which the longitudinal bores discharge.

14. A flowmeter as in Claim 13, wherein the chamber is a counterbore of the axial bore in which the plunger slides.

15. Aflowmeter as in any one of Claims 10 to 14, wherein the end caps are provided with screwthreaded counterbores to enable the flowmeter to be connected in a pipeline.

16. A flowmeter substantially as hereinbefore described with reference to Figures 1 to 5 of the accompanying drawings or as modified in Figure 6 or Figure 7 of the accompanying drawings.