Valve disc and drive shaft assembly

Abstract: A butterfly valve disc (10) has a circular cross-section bore (26) for receiving the end of a drive shaft (16) which engages with a member (20) non-rotatably located in the bore (26). The member (20) is polygonal and preferably formed with twelve sides (75) and edges (70), the edges (70) biting into the internal surface of the bore (26) to prevent rotation. The member (20) preferably is of harder alloy than the disc (10) to resist wearing and is formed with a slot (30) extending perpendicularly to the plane of the disc (10) to receive a corresponding tongue (36) formed at the end of the shaft (16). This arrangement allows a small degree of play so that if the disc (10) is subjected to pressure on one side and therefore bends, the torque required to open the valve is not increased. Alternatively wherein the disc (10) (or another component) is not subject to such pressure the member (20) may be integrally formed with the shaft (16).

Description: This invention relates to a valve disc and drive shaft assembly, particularly for a butterfly valve. In a known form of butterfly valve, the disc is cast to its general shape and then a diametrically arranged bore is formed by drilling. This bore extends across the whole diameter of the disc, and receives the drive shaft by means of which the disc is rotated to open or close the valve. To prevent the shaft rotating in the bore, one or more pins are provided radially with respect to the shaft axis and inserted through holes in the disc into blind apertures formed in the shaft. However, it has been found that sometimes the joint between a pin and a disc is not properly formed or becomes damaged and leakage occurs, either through the disc from one side to the other or from the interior to the exterior of the valve, along a leakage path alongside the drive shaft. One way of avoiding piercing the disc is to use a shaft of non-circular cross-section e.g. square cross-section, in a correspondingly shaped bore. However such bore shapes are relatively difficult and expensive to provide in practice to the required degree of accuracy by relatively simple machining techniques. AU - B - 545829 discloses a shaft with a splined end portion pressed into a bore at the edge of a valve disc. The resultant assembly is rigid, the shaft being effectively integral with the disc and the assembly will be difficult to rotate from the closed position to the open position if an elevated pressure is applied to the disc tending to bend or flex the disc. Further, if the material of the shaft is harder than that of the disc, continued operation will loosen the splined end in the bore because the material of the disc adjacent the bore side will be distorted by the high local pressure applied by each spline. It is an object of the present invention to provide a valve disc and drive shaft assembly with a relatively simple and inexpensive means for non-rotatably securing the disc to the shaft. In accordance with the invention a valve disc and drive shaft assembly comprises a disc formed with a blind bore of circular cross-section extending radially inwardly from the disc periphery, characterised in that a member with regular polygonal cross-section outer surface, having a plurality of sides and edges and having a non-circular aperture for receiving a correspondingly shaped projection on the end of the shaft, is non-rotatably located within the bore, the construction and arrangement being such that a torque applied to the shaft is transmitted to the member and thence to the disc. In accordance with another aspect of the invention a method of driveably connecting a drive shaft to a valve disc comprising forming a blind bore of circular cross-section to extend radially inwards from the disc periphery, is characterised by forming a member with a regular polygonal cross-section outer surface having a plurality of sides and edges and a non-circular aperture, non-rotatably locating the member with the bore, forming the end of the shaft with a projection having a shape corresponding to that of the aperture, and locating the projection in the aperture, the assembly so formed being capable of transmitting a torque applied to the shaft, to the member and thence to the disc. Preferably the edges of the member are regularly spaced around the periphery of the member. The distance across the member between opposite edges is slightly greater than the internal diameter of the bore so that a force has to be applied to insert the member into the bore and, when in position the edges press against the interior surface of the bore. The edges may indent the interior surface and displace or deform the material of the disc. Preferably the member is made of a material which is of superior strength or hardness compared to the material of the disc and has a higher wear resistance. For example the member may comprise a high strength alloy e.g. hardened stainless steel whereas the disc material has a lower strength or hardness e.g. case S.G. iron for inexpensiveness, ease of manufacture and/or corrosion resistance. The member may be formed to have twelve sides and edges each regularly spaced-apart around the periphery of the member. The sides may be flat or concave. In one preferred form of the invention the end of the shaft is formed with a tongue which extends diametrically, the length of the tongue, measured across the shaft, being slightly less than the diameter of the shaft, and the member is formed with a slot for receiving the tongue, the slot extending across the whole width of the member perpendicularly to the plane of the valve disc. Thus when the valve is closed and one side of the valve disc is subjected to fluid pressure the disc bends or otherwise moves slightly so that the member slides relatively to the tongue. No high bending movements are transmitted from the disc to the shaft so that the valve may be opened readily without the need for a high torque to be applied. The invention will now be described by way of example only with reference to the accompanying drawings of which:- Figure 1 is a side view of the valve disc of a butterfly valve; Figure 2 is a plan view of the valve disc shown in Figure 1; Figure 3 is a cross-sectional view of the valve disc shown in Figures 1 and 2; Figure 4 is an exploded partial side view, partly in cross-section, of the disc, the member and associated drive shaft of the butterfly valve according to the invention; Figure 5 is a plan view of the member shown in Figure 4; Figure 6 is an end view of the shaft shown in Figure 4; Figure 7 is a cross-sectional view of the valve disc and member of the butterfly valve according to a modification of the invention; and Figure 8 is an exploded partial perspective view of part of the drive shaft, the member and part of the valve disc of the butterfly valve according to the modification of the invention. The valve of the present invention shown in the drawings comprises a disc 10, a member 20, and a drive shaft 16. As shown in Figure 1 the valve disc 10 of a butterfly valve has an upper socket 12 and a lower socket 14, cast from S.G. iron as a single unit and subsequently machined to its final shape. The disc is supported between an upper drive shaft 16 (partially shown in Figure 4) and a lower mounting shaft (not shown). The upper drive shaft is housed in a conventional housing in the body of the valve and is provided with seals in a conventional manner. Details are not given nor shown in the drawings as they are not relevent to the present invention. A handle or actuator (not shown) is provided at the upper end of the drive shaft in order that the valve may be opened or closed. The upper socket 12 of the valve disc 10, as can be seen particularly in Figures 2 and 3 is provided with a bore 26, accurately machined or drilled to the required size and shape. As shown especially in Figure 3, the diameter of the outer part 26a of the bore is slightly larger than the inner part 26b. The lower socket 14 is also formed with a bore 34, of constant diameter. The member 20, made of hardened stainless steel, of the valve of the first embodiment of the invention, shown in Figures 4 and 5, is generally cylindrical and has a chamfered lower edge 22. The length (depth) of the member is approximately equal to half the depth of the bore 26. The member is formed with a central bore 28 extending for the whole length (depth) thereof and a rectangular slot 30 extending across a diameter of the upper surface and having a depth approximately equal to two thirds of the length of the member 20. As can be seen particularly in Figures 5 or 8 the member 20 is regularly polygonal in cross-section i.e. having a plurality of flat surfaces 75 (see Figure 5) or concave surfaces (see Figure 8) and edges 70, the latter extending parallel to one another and to the axis of the member. As shown the member 20 has twelve flat or concave surfaces 75 and twelve edges 70. The maximum diameter M-M of the member 20, measured across the member between two opposite edges, is less than the internal diameter of the outer part 26a of the bore 26 and is greater than the internal diameter of the inner part 26b of the bore 26 in the upper socket 12 of the valve disc 10, and the minimum diameter L-L measured across the member between the two opposite surfaces 75 is equal to or slightly less than the internal diameter of the inner part 26b of the bore 26. This means that the member 20 is inserted readily into the outer part 26a of the bore 26, and a force has to be applied to locate the member in the inner part 26b where the edges 70 bite into the side of the bore to prevent rotation of the member with respect thereto. The drive shaft 16 shown in the upper part of Figure 4 is formed with a tongue 36 extending diametrically across the end face 38 of the shaft. The tongue has a size and shape complementary to the rectangular slot 30 formed in the member 20, but the diametric length of the tongue is slightly less than the diametric length of the slot 30. This allows the tongue 36 to move slightly in the slot 30 if the disc moves or bends under fluid pressure. The end face 38 of the drive shaft 16 is accurately machined so that it is at right angles to the shaft axis. The circular cross-section shaft locates in the main bore 26 of the upper socket 12 and the shaft axis is in alignment with the axis of the bore 26. Diametrically opposite the upper socket 12 of the valve disc 10 is a lower socket 14 formed with a bore 34 and having a conical base 37 formed by a drilling operation. This bore 34 formed in the lower socket receives the upper end of the lower supporting shaft (not shown). The lower supporting shaft and the lower socket act as a bearing for the valve disc. The bore 34 in the lower socket 14 and the upper end of the supporting shaft accurately locate the valve disc 10 in the required position in the valve. Adjacent the upper and lower sockets the periphery of the valve disc is formed with two flat surfaces 40, 42 in a conventional manner and the two generally semi-circular parts of the periphery of the valve disc are machined to have a profiled edges (generally semi-circular in cross-section) as shown particularly at 44 in Figure 2 to provide sealing engagement with a rubber seal formed within the bore of the valve body (not shown). When the valve is assembled together the member is positioned inside the bore 26 in the upper socket as described above. The end face 38 of the drive shaft 16 abuts the upper surface of the member and the tongue 36 is accurately positioned within the slot 30. On operation of the valve a torque is applied by the handle or actuator attached to the upper end of the drive shaft 16 and this is transmitted via the tongue 36 to the member 20 and thence via the edges 70 to the valve disc to open or close the valve. It has been found that particularly for drive shafts of ½" to 1" (12.5 mm to 25 mm approximately) nominal diameter a member having a regular polygonal cross-section and twelve edges and twelve faces is particularly efficient for transmitting torque from the shaft to the disc and has an acceptable push-in force (see below). It was also found that if the number of edges was increased there was a loss of shear strength on the assembly, and if the number of edges was decreased then the push-in force i.e. the force required to push the member into the inner part of the bore, was increased. These results are illustrated in Table 1 below and were obtained using members having a dimension measured between opposite faces equal to the internal diameter of the bore, and the dimension measured between opposite corners being maintained at a constant value. Material of shaft Stainless steel containing 17% Cr and 4% Ni ASTM A 564 Type 630 Tensile Strength 930 MPa Yield Strength 725 MPa Material of member Stainless Steel containing 17% Cr and 4% Ni ASTM A 564 Type 630 Tensile Strength 930 MPa Yield Strength 725 MPa Material of disc Spheroidal Graphite Cast Iron Type CEN pr EN TC190/230 gr 400-15 (British Standard 2789 Gr 420-12) Tensile strength 420 MPa Yield strength 270 MPa Diameter of shaft 25.00 mm Tongue width 9.00 mm Diameter of bore in disc 25.05 mm (Outer part) 24.00 mm (Inner part) (P) Distance across opposite faces of member (L-L) 23.95 mm (12 faces) Distance across opposite edges of member (M-M) 25.00 mm (12 edges) (Q) Interference (Difference between dimensions P and Q above) 1.00 mm Furthermore it was also found that by modifying the member to make the faces (75) concave (see Figure 8) to torque transmission was improved (see Table 2 below). Material of shaft As Table 1 above Material of member As Table 1 above Material of disc Aluminium Bronze British Standard 1400 AB2 Tensile Strength 640 MPa Yield Strength 250 MPa Diameter of shaft 25.00 mm Tongue width 9.00 mm Diameter of bore disc 25.05 mm (outer part) 24.00 mm (Inner Part) (P) Distance across opposite faces of member (L-L) 23.95 mm (12 flat faces) Distance across opposite edges of member (M-M) 25.00 mm (12 edges) (Q) Interference (Difference) between dimensions Part Q above 1.00 mm The members 20 described above are made simply and inexpensively by conventional metal machining techniques and provide a simple and effective means for transferring the torque from a drive shaft 16 to a valve disc 10. Since the valve disc is not pierced in any way on either of its main surfaces 60, 64 the likelihood of any leakage occurring from one side of the disc to the other or to the exterior of the valve along the surface of the drive shaft 16 is eliminated. The invention, in allowing material of superior strength to be used for the torque drive member 20, e.g. a high strength alloy or hardenable stainless steel, means the valve drive components will have a high resistance to wear, and high strength for torque transmittal inside disc member 10, which for purposes of economy or corrosion resistance, will require to be made of a material of much lower strength. The central aperture 28 also provides a passage to the lower side of the member 20 should the member need to be removed from the bore 26. A member in accordance with the present invention will find application in other engineering devices where it is required to transmit the torque from, for example, a shaft, to a component in a simple and effective manner. In the embodiment of the invention described the tongue/slot connection is weaker than the member/disc connection, but the assembly allows movement of the disc as a result of fluid pressure applying a force which is radial with respect to the drive shaft.

Claims: A valve disc (10) and drive shaft (16) assembly comprising a disc (10) formed with a blind bore (26) of circular cross-section extending radially inwardly from the disc periphery (44), characterised in that a member (20) with a regular polygonal cross-section outer surface, having a plurality of sides (75) and edges (70) and having a non-circular aperture (30) for receiving a correspondingly shaped projection (36) on the end of the shaft (16), is non-rotatably located within the bore (26), the construction and arrangement being such that a torque applied to the shaft (16) is transmitted to the member (22) and thence to the disc (10). A valve disc and drive shaft assembly according to Claim 1 characterised in that the member (20) has twelve sides (75) and edges (70). An assembly according to Claim 1, or Claim 2 characterised in that the edges (70) of the member (20) are regularly spaced around the periphery thereof and the distance across the member (20) between opposite edges (70) is slightly greater than the internal diameter of the bore (26), so that a force has to be applied to insert the member (20) into the bore (26) and, when in position, the edges (70) press against the interior surface of the bore (26) to prevent rotation. An assembly according to any one of the preceding claims characterised in that the member (20) is made of a material which is of superior strength or hardness compared to the material of the disc (10) and has a higher wear resistance. An assembly according to any one of the preceding claims characterised in that the peripheral edge (22) of the member (20) adjacent the base of the bore (26) is chamfered. An assembly according to any one of the preceding claims characterised in that the peripheral faces (75) of the member (20) are flat. An assembly according to any one of Claims 1 to 5 characterised in that the peripheral faces (75) of the member (20) are concave. An assembly according to any one of the preceding claims characterised in that the bore (26) has an inner part (26b) and an outer part (26a) having a diameter greater than the inner part (26b), the member (20) being non-rotatably located in the inner part (26b). An assembly according Claim 8 characterised in that the shaft (16) is of circular cross-section and is located in the outer part (26a). An assembly according to any one the preceding claims characterised in that the projection (36) at the end of the shaft (16) is shaped as a tongue (36) which extends diametrically , the length of the tongue (36), measured across the shaft (16), being slightly less than the diameter of the shaft (16), and the member (20) being formed with a slot (30) for receiving the tongue (36), the slot (30) extending across the whole width of the member (20) perpendicularly to the plane of the valve disc (10). A method of drivably connecting a drive shaft (16) to a valve disc (10) comprising forming a blind bore (26) of circular cross-section to extend radially inwards from the disc periphery (44), characterised by forming a member (20) with a regular polygonal cross-section outer surface having a plurality of sides (75) and edges (70) and a non-circular aperture (30), non-rotatably locating the member (20) within the bore (26), forming the end of the shaft (16) with a projection (36) having a shape corresponding to that of the aperture (30) and locating the projection (36) in the aperture (30), the assembly so formed being capable of transmitting a torque applied to the shaft (16), to the member (20) and thence to the disc (10). A method according to Claim 11 characterised in that the member (20) is formed with a plurality of concave faces (75) regularly spaced-apart about the periphery thereof. A method according to Claim 11 characterised in that the member (20) is formed with a plurality of flat faces (75) regularly spaced-apart about the periphery thereof. A method according to any one of Claims 11, 12 and 13 characterised in that the member (20) is formed with twelve sides (75) and edges (70). A method according to any of Claims 11, 12, 13 or 14 characterised in that the bore (26) is formed with an inner part (26b) and outer part (26a), the member (20) is located in the inner part (26b) and the shaft (16) is formed to have a circular cross-section and is located in the outer part (26a).

Inventors: HASELEY PHILIP JOHN, MORRIS MICHAEL PATRICK, HASELEY, PHILIP JOHN, MORRIS, MICHAEL PATRICK
Applicants: BTR PLC
Application year: 1992
Main classification: F16K1
IPC codes: F16K1