GB2052762A - Dry gas meter - Google Patents

Abstract

To permit adjustment of a gas meter having measuring chambers each with a flexible diaphragm free to reciprocate and operate valves admitting gas to the chambers, the drive from the diaphragms to the valves includes an adjustable crank assembly. Crank arms (25, 26) connected to the diaphragms are secured by a resilient pin (27) spring fitted to one of a number of bores (30) in a tangent member (28), rotatable on a spindle (31) which drives the valves via arms (39). A worm wheel (33) mounted on tangent member (28) drives a rack member (23) secured to the spindle. Rotation of the worm wheel rotates the tangent member with respect to the spindle and so adjusts the phase relationship between the diaphragm and the valves. The bores (30) are at different radii allowing the throw of the crank arms to be varied. <IMAGE>

Description

SPECIFICATION Dry gas meters This invention relates to gas meters having one or more chambers each with a flexible diaphragm free to reciprocate back and forth, which back and forth movement operates valves admitting gas to the chambers. Such gas meters will be referred to hereinafter as "dry gas meters".

Dry gas meters require to be adjusted to achieve their nominal working characteristics by setting the phase relationship of the valves and diaphragms. Such adjustments as for instance described in U.K. patent No. 725,118 have involved skilled setting operations.

This invention provides a dry gas meter having an adjustable crank assembly for translating reciprocating movements derived from the diaphragms into a rotational movement of a spindle which directly or indirectly drives the valves, said crank assembly comprising a tangent member rotatable on said spindle and carrying a worm wheel, a rack member secured to rotate with said spindle and carrying a circular rack engaged with said worm wheel, and crank arms secured to said tangent member to rotate it, said crank arms being connected to be reciprocated by movements derived from the diaphragms. This arrangement allows the tangent member to be rotated via the worm wheel relative to the spindle, thereby adjusting the phase relationship between the diaphragm position and the valve openings.

The tangent member may comprise a partcircular member, said worm wheel being mounted in spaced bearings at one side so that a worm gear of said wheel protrudes from the member.

The rack member may comprise a disc located closely adjacent the tangent member so that the rack engages the protruding worm gear.

The tangent member may also have a plurality of locations for attachment of the crank arms, each location having a different radial distance from the spindle axis, whereby the throw of the crank arms may be selected. Said locations may comprise bores into which a common pin made of a resilient material for the crank arms may be removably spring-fitted.

The worm wheel may be rotated positively to any desired position so easily setting the phase relationship without any great skill. Moreover, when the phase relationship has been so set the correct crank arm throw can be achieved by "popping" the pin for the crank arm into the selected bore. The whole adjustment procedure therefore becomes simple and positive, losing the delicacy and skill required from previous arrangements.

A specific embodiment of the invention is shown in the accompanying drawings, in which: Figure 1 is an exploded view of the main working parts of a dry gas meter, Figure 2 is a section through a gear box and a crank assembly of the gas meter of Figure 1, Figure 3 is a detail plan view of a tangent member of the gas meter of Figure 1, Figure 4 is a view of a worm of the dry gas meter of Figure 1.

The dry gas meter shown in Figure 1 is of the kind comprising a pair of chambers 11, 12 mounted side by side, each having a reciprocating diaphragm 14 to either side of which gas is admitted via reciprocating valves 1 5, 1 6, in conjunction with valve seat 17, and exhausted via exhaust tube 23.

The reciprocating movements of the diaphragms are used both to drive the valves and to measure the gas volume flowing. The movements are transmitted to oscillating flag rods 18, 1 9 having oscillating flag arms 20, 21. The flag arms are connected to drive a gear box 22 through a crank assembly shown best in Figures 2 to 4.

The flag arms are connected to two crank arms 25, 26, each of which has one end pivotally mounted on a common pin 27, which pin is removably spring-fitted into a bore in a tangent member 28. The ends of the pin are slightly oversize with respect to the diameter of the bores so that the ends may be forced into the bores by resilient deformation, and spring back to their original size when fully inserted. As seen best in Figure 3, the tangent member 28 is part circular in plan having a central pivot opening 29 and four bores 30. The pin 27 may be fitted into any selected one of the four bores 30 which are at slightly different distances from the pivot opening 29. Therefore, the throw of the crank arms (the radial distance from the central pivot opening) may be selected for the gas meter by the choice of bore 30.

A spindle 31 of the gear box passes through the central pivot opening 29 and the tangent member 28 may be rotated relative thereto by a rack and worm wheel drive. The worm wheel 33 (Figure 4) formed integrally with a pin, has its ends sprung into engagement with bearing openings 34 in the tangent member so that the worm gear protrudes and engages an annular rack gear on a discshaped rack member 35. The disc is secured to rotate with the spindle 31 adjacent the tangent member. One end of the worm wheel has a slot which may be engaged by a screwdriver to rotate it, tending to move the rack member and tangent member in opposite directions. Since the rack member 35 is fixed to the spindle 31 it resists movement, so the tangent member which presents less resistance, is caused to rotate about the spindle.Thus the angular position of the crank arms relative to the spindle is adjusted by the rotation of the worm wheel. In use, the pressure of the crank arms on the tangent member produces forces parallel to the plane of the tangent member which do not include any force in the sense to rotate the worm wheel. The worm wheel therefore acts simply as a solid connection between the tangent member and the rack member and a drive path is maintained through the tangent arm and rack member to the spindle. No special locking device for the worm wheel is therefore required.

The spindle 31 extends into the gearbox 22 and carries a spiral gear driving an index spindle 37. A first magnet 38 of a magnetic coupling is carried by spindle 37 and drives an index (not shown) whereby the volume of gas flowing through the meter is measured.

The upper end of the spindle 31 is secured to further crank arms 39, to which levers driving the valves 15, 16 are secured. The spindle 31 therefore drives both the index and the valves. The adjustment of the angular position of crank arms 25, 26 with respect to the spindle described above effectively alters the phase relationship between the movements of the diaphragms and the opening and shutting of the valve.

The crank arms 25, 26, tangent member and worm wheel, and disc 35 are formed of a resilient plastics material, e.g. acetal, which allows the parts to be sprung into and out of engagement with one another.

When the gas meter is being adjusted to provide a required performance, the phase relationship of the valve opening and the position of the diaphragm is set. This setting, however, affects the travei of the diaphragm in its reciprocating motion since the diaphragm slows down and stops moving when the respective exhaust passage is opened. Accordingly, to arrange for the correct diaphragm length of movement the throw of the crank arms is adjusted as described above by selection of bore 30.

The gas meter adjustment can therefore be made using only simple tools, a screwdriver to adjust the phase relationship and springing the pin 27 into the appropriate bore. It will be noted that although pin 27 may be readily removed from the bore, in use the forces on the pin are not such as to tend to remove it from the bore.

Claims (5)

1. A dry gas meter of the kind having an adjustable crank assembly for translating reciprocating movements derived through crank arms (25,26) from the diaphragm (14), into a rotational movement of a spindle (31) which ,directly or indirectly drives the valves (15, 16), characterized by said adjustable crank assembly comprising a tangent member (28) mounted' rotatably on said spindle and carrying a worm wheel (33), and a rack member (35) secured to rotate with the said spindle and carrying a circular rack gear engaged with said worm wheel (33), said crank arms (25, 26) being releasably secured to the tangent member to rotate it, whereby the tangent member may drive through the worm wheel and rack member to rotate the spindle.

2. A dry gas meter as claimed in claim 1, further characterized by said tangent member (28) being part-circular and providing a pair of spaced bearings (34) for the worm wheel (33) whereby the worm wheel is rotatably supported with the gear thereof protruding from the plane of the tangent member, and by said rack member (35) being a disc closely adjacent the tangent member so that the rack gear engages the protruding worm gear.

3. A dry gas meter as claimed in claim 1 or claim 2, further characterized by said tangent member (28) having a plurality of locations (30) for the selective attachment of the crank arms (25, 26) whereby the throw of the crank arms may be selected.

4. A dry gas meter as claimed in claim 3, further characterized by said tangent member (28) being formed of a resilient plastics material, said locations (30) comprising a plurality of bores at different radial distances from the spindle axis, and said crank arms being secured to any one of said bores by a pin (27) of resilient plastics material having an oversize end which may be forced through the selected bore.

5. A dry gas meter as claimed in claim 4, further characterized by said crank arms (25, 26) also being formed of a resilient plastics material and having openings through which said pin (27) may be forced to form a spring fit.