BLEEDER VALVE ASSEMBLY

Abstract: A valve assembly has a valve lid (3) assembly which can be fitted in sealing relation on a valve seat (2), an over-centre device can serve to force the lid on to the seat; a drive shaft (A) connected to the lid assembly and drive means (10) for rotating the shaft to open and close the valve seat, the over-centre device serving to oppose rotation of the shaft up to a critical position whereupon the device assists in rotation of the shaft to open the valve seat.

Description: This invention relates to a bleeder valve assembly of the type comprising a valve seat with a removable lid which can be fitted in sealing relation on the valve seat. A fluid-operated piston-cylinder device normally operates to lift the lid from the seat and to replace the lid on the seat to thereby control the pressure of fluid in the apparatus to which the assembly is fitted. In the event of a malfunction preventing the piston-cylinder device from lifting the lid from the valve seat, the pressure of the fluid in the apparatus must be allowed to raise the lid to quickly lower the pressure in the apparatus. An example of a bleeder valve assembly of the aforementioned type is disclosed in British Patent 1523578, (equivalent to FR-2348422). The relevant features of GB 1523578 are acknowledged in the precharacterising part of claim 1 of this application. It is an object of the present invention to further develop the generic bleeder valve assembly, particularly for the relief of over pressure in a furnace. According to the present invention there is provided a valve assembly comprising a valve seat, a lid structure including a valve lid which can be fitted in sealing relation on the valve seat, said lid structure being secured towards one end of an arm, the arm being mounted on a rotatable shaft (A) to rotate therewith about a common axis longitudinally remote from the lid structure, an over-centre spring device arranged to apply a force to the shaft to rotate the shaft, and drive means arranged to rotate the shaft; the arrangement being such that, with the valve lid fitted on the seat, the spring device acts to urge the shaft in the direction to seal the lid on the seat and, when the shaft is rotated in the direction to displace the lid from the seat, the rotation of the shaft is opposed by the spring device until the over-centre position is exceeded whereupon the spring device assists in the rotation of the shaft; and characterised in that the lid structure is secured to the arm by first pivot means and is further secured to an elongate link (6) by second pivot means at a point spaced from the first pivot means, the link being mounted to rotate about a fixed pivot axis spaced from the shaft so that during displacement the lid structure rotates about two axis. The drive means is conveniently a hydraulic or a pneumatic cylinder which acts through a lever arm on the shaft. The cylinder is a double-acting cylinder which enables the shaft to be rotated in both directions of rotation. The over-centre spring device is conveniently connected to a link connected to the shaft and it provides a "snap-action" when the lid is lifted from the valve seat beyond the over-centre position of the device. When the lid is fitted on the valve seat the spring device serves to urge the shaft in the direction to force the lid device into sealing relation with the valve seat. In order that the invention may be more readily understood, it will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a side elevation of the valve assembly in its closed position; Figure 2 is a side elevation of the valve position with the lid partly opened; and Figure 3 is a side elevation of the valve assembly with the lid fully open. A valve assembly 1 is fitted on to a device, such as a furnace, the details of which are not shown. The valve assembly has a spherical valve seat 2 on which a valve lid 3 can be fitted to form a sealing relation therewith. In the arrangement shown, a lid structure consists of the valve lid 3 which is in the form of a disc rigidly mounted within a U-shaped frame 4. A lever 5 secured at one end to a rotatable shaft A is pivotably connected at its opposite end to one side of the U-shaped frame 4. A hydraulic or pneumatic piston-cylinder device 10 is trunnion mounted and its piston rod is connected to one end of a link 7 secured at its other end to the shaft A. Thus, when the piston cylinder device, which is a double-acting device, is actuated, the lid is raised and lowered with respect to the seat of the valve assembly by pivoting about shaft A. A further link 6 is pivotally connected to the frame 4 and to a pivot point B and this link causes the lid structure to pivot about point B when it is raised and lowered by the rotation of the shaft A. Thus the lid structures rotates about two axis simultaneously. A further link 8 secured at one end to the shaft A is pivotally connected at its opposite end to a spring device 9 which is mounted in a pair of pivotable links 11 which are secured to a pivot axis C. In the arrangement shown in Figure 1, the action of the spring in the housing of the device is urging the arm 8 in the anti-clockwise direction to force the lid firmly on to the valve seat. When the piston cylinder device 10 is actuated to force out the piston rod, rotation of the shaft A occurs and the arm 5 is rotated in the clockwise direction to displace the lid 3 from the seat of the valve. When the lid is first displaced, the action of the spring device 9 is such as to oppose the rotation of the shaft but, at the position shown in Figure 2, the line of action of the spring device is aligned with the axis of the arm 8, this being known as the over-centre position. Further movement of the shaft A in the clockwise direction causes the spring device 9 to pass through the over-centre position and it then bears upon the arm 8 to rotate the shaft on the clockwise direction. The continuing movement of the lid is thus as a result of the action of the spring device acting in concert with the piston-cylinder device. In Figure 3 the valve assembly is shown in its fully open position where the lid 3 is sufficiently far away from the valve seat as not to impede the flow of gases from the apparatus to which the valve assembly is fitted. In use, therefore, the valve lid is normally opened and closed by the piston-cylinder device 10 acting through the shaft A and the arm 5 on to the lid structure 4 to relieve over pressure in the apparatus to which the valve is fitted. The pressure in the apparatus is detected by sensors (not shown) which serve to control the device 10. In the event of power failure to the piston-cylinder device, over pressure in the apparatus to which the valve is fitted is relieved by the increase in pressure lifting the lid against the action of the spring device sufficiently to allow the over pressure to be reduced. When the over pressure is reduced, the lid will then return to its position on the seat. In the event of a massive over pressure, the lid is displaced to the fully open position shown in Figure 3 by the action of the pressure lifting the lid through the over-centre position and thereafter the spring pressure fully opens the lid.

Claims: 1. A valve assembly comprising a valve seat (2), a lid structure (4) including a valve lid (3) which can be fitted in sealing relation on the valve seat (2), said lid structure (4) being secured towards one end of an arm (5), the arm (5) being mounted on a rotatable shaft (A) to rotate therewith about a common axis longitudinally remote from the lid structure (4), an over-centre spring device (9) arranged to apply a force to the shaft (A) to rotate the shaft (A) and drive means arranged to rotate the shaft (A); the arrangement being such that, with the valve lid (3) fitted on the seat (2), the spring device acts to urge the shaft (A) in the direction to seal the lid (3) on the seat (2) and, when the shaft (A) is rotated in the direction to displace the lid (3) from the seat (2), the rotation of the shaft (A) is opposed by the spring device until the over-centre position is exceeded whereupon the spring device (9) assists in the rotation of the shaft (A); and characterised in that the lid structure (4) is secured to the arm (5) by first pivot means and is further secured to an elongate link (6) by second pivot means at a point spaced from the first pivot means, the link (6) being mounted to rotate about a fixed pivot axis (B) spaced from the shaft (A) so that during displacement the lid structure (4) rotates about two axis. 2. An assembly according to claim 1 in which the arm (5) is provided by a air of arms (7, 8) which are spaced one from the other to rotate about the common axis of shaft (A) and, the elongate link (6) is provided by apair of links spaced one from the other to rotate about the common fixed pivot axis (B) and the lid structure comprises a U-shaped frame under which the valve lid is rigidly fastened. 3. An assembly according to claim 2 in which the spring device (9) comprises a housing; a spring acting between the housing and one arm (8) of said pair of arms mounted on the shaft (A); and a pair of links (11) pivotally secured to the housing and to a further fixed pivot axis (C).

Inventors: STAMP, GEORGE WILLIAM
Applicants: DAVY MCKEE (STOCKTON) LIMITED
Application year: 1988
Main classification: F16K17
IPC codes: F16K17, F27D1