Valve assembly

Abstract: A valve comprises a valve stem 2 surrounded in part by a packing material 3, and compression means arranged to bring the packing material into sealing engagement with the valve stem. The compression means includes a spring assembly comprising resilient springs 21 enclosed within a housing member 22 having a closure member 23 slidably mounted within it. The housing member 22 and the closure member 23 are provided with engagement means 27,28 acting to retain the closure member 23 captive within the housing member 22.

Description: This invention relates to valves, and in particular to spring assemblies used to exert a compressive force on valve packing materials. Valves used, for example, for controlling the flow of liquids in pipelines, eg in petrochemical plants, commonly include a valve stem which passes into the valve body. The valve stem must be suitably sealed at its point of entry into the valve body, in order to prevent leakage of the liquid. The seal is usually formed by a packing material arranged around the valve stem and compressed by a sleeve known as a gland to make a tight joint. The pressure exerted by the gland keeps' the packing tightly pressed against the valve stem. In valves of this type, known e.g. from DE-C-39 37 316 and US-A-4 582 329, it is important that the pressure exerted by the gland on the valve packing is neither too great nor too small. If the pressure is too great, the valve may be difficult to operate; if the pressure is too small, leakage may occur. For this reason, it is common to use calibrated spring assemblies to act on the gland. The optimum compressive force depends inter alia on the nature of the packing material and the various dimensions of the valve components, and can be calculated. A spring assembly producing this optimum force may then be prepared and utilised. Such spring assemblies commonly comprise a stack of annular disc springs which are housed in a cup shaped housing. The base of the housing has a central aperture which enables the assembly to be positioned about a screw-threaded stud, one end of which is fixed in the valve body and which passes through an aperture in the gland. A support washer is then placed on top of the spring assembly and tightened with a nut. Once tightened, the stack of springs acts between the support washer and the base of the housing, exerting the required force on the gland. A disadvantage of spring assemblies of the type described is their loose assembly. This means that the integrity of the disc spring stack is easily lost prior to installation or during maintenance work. For the correct force to be exerted, it is necessary that the correct number of disc springs be used, and also the correct sequence. If the number and/or sequence of disc springs is incorrect, insufficient force may be exerted on the packing, leading to the danger of potentially hazardous leaks. Another disadvantage is that the support washer may be over-tightened, leading to excessive compressive force on the packing and difficulties in.valve operation. Furthermore, a valve as defined by the features of the preamble portion of claim 1 is known from prior art document US-A-3 968 970. There has now been devised an improved form of spring assembly for use in a valve which overcomes or substantially mitigates the above mentioned disadvantages. According to the invention there is provided a valve with the features of claim 1. The valve according to the invention is advantageous primarily in that the integrity of the spring assembly is maintained by the fact that it is enclosed within and between the housing member and the closure member. The springs are not dislodged in the event that the unit is dropped or mishandled, and the sequence of springs cannot accidentally be changed. In addition, the assembly may be supplied as a complete unit, thereby simplifying installation. According to another aspect of the invention there is provided a spring assembly for use in association with a valve having the features of claim 1. The spring means is preferably a stack of annular disc springs of generally conventional form. The diameter of the disc springs is preferably only slightly less than the internal diameter of the cup member. This enables the walls of the cup member to act as guides, eliminating the need for special studs or spring guides. Apart from the spring assembly, the compression means may comprise a generally conventional gland, eg a sleeve bearing on the packing material and provided with a flange acted on by the spring means. The lug(s) are most preferably formed on the closure member and the recess(es) on the internal walls of the housing member. Most preferably, there are provided one pair of lugs and one pair of recesses, located at diametrically opposed positions on the closure member and the housing member respectively. It is particularly preferred that the engagement means should be such that disengagement of the housing member and the closure member, whilst difficult or impossible during normal use, should be possible for the purposes of assembly or maintenance of the spring assembly. The longitudinal recess in the internal wall of the housing member is therefore preferably provided with a by-pass recess intermediate its ends, the by-pass extending from the longitudinal recess to the upper edge of the housing member. When removed from the valve, the resilience of the springs will urge the closure member to the upper limit of its travel within the housing member. However, by application of suitable downward force and a twisting action, the lugs on the closure member may be transferred into the by-pass recess, enabling the closure member to be removed and the assembly disassembled. Downward travel of the closure member relative to the housing member is limited by the length of the longitudinal recess, preventing the expression of excessive force on the valve packing. Thus it is a further preferred feature of the invention to provide stop means limiting the travel of the closure member within the housing member. The invention will now be described in more detail, by way of illustration only, with reference to the accompanying drawings, in which Figure 1 is a sectional view of part of a valve according to the invention, Figure 2 is a sectional view of a cup member forming part of the valve of Figure 1, Figure 3 is a plan view of the cup member of Figure 2, Figure 4 is an enlarged view of part of the cup member of Figure 2, and Figure 5 is side elevation of a support washer used in conjunction with the cup member of Figure 2. Referring first to Figure 1, a valve comprises a valve body 1 in which passes a valve stem 2. The joint between the valve body 1 and the valve stem 2 is sealed by rings of packing material 3. The packing material 3 is compressed into sealing engagement with the valve stem 2 by a gland assembly comprising a cylindrical gland follower 4 and a gland flange 5. Threaded gland studs 6,7 are located in threaded bores in the valve body 1 and pass through apertures in the gland flange 5. A spring unit comprising a stack of annular disc springs 21 enclosed within a cup member 22 and a support washer 23, is mounted on each of the gland studs 6,7 (in Figure 1 only one spring unit is shown). The spring unit is clamped in place by a nut 8 threaded onto the gland stud 6. Both the cup member 22 and the support washer 23 are of stainless steel. As is seen most clearly in Figures 2 and 3, the cup member 22 is a hollow cylinder open at the top and having a central aperture 24 in its base to receive the gland stud 6,7. The disc springs 21 similarly have central apertures, as does the support washer 23 (shown by the dashed lines in Figure 5). The support washer 23 is provided at diametrically opposed positions with a pair of hemispherical lugs 25,26. The cup member 22 is provided on its internal wall, again at diametrically opposed locations, with a pair of recesses 27,28 of semicircular section. The form of the recesses 27,28 is shown most clearly in Figure 4. As can be seen, the recess 27 has a first longitudinal portion 30 extending from a point a short distance below the upper edge of the cup member 22. A short distance below the upper limit of the first longitudinal portion 30 there is provided a branch portion 31 which connects to the lower end of a second longitudinal portion 32 which extends to the upper edge of the cup member 22. The spring unit is assembled by inserting the stack of disc springs 21 into the cup member 22. The lugs 25,26 on the support washer 23 are then aligned with the upper end of the second longitudinal portions 32 of the recesses 27,28, and the support washer 23 inserted into the cup member 22. By the application of downward pressure (eg from a suitable mechanical jig) and twisting, the support washer 23 is forced into the cup member 22, the lugs 25,26 following the line of the recesses 27,28 to the position shown by the dashed lines in Figure 4. In this position, the resilience of the disc springs 21 retains the support washer 23 captive within the cup member 22. The downward force necessary to dislodge the support washer 23 is generally far greater than can be applied manually. In use, the assembled spring unit is positioned over the gland stud 6,7 and the nut 8 threaded onto the stud 6,7. Prior to tightening of the nut 8, with the lugs 25,26 in the position shown by the dashed lines in Figure 4, the upper surface of the support washer 23 protrudes somewhat from the cup member 22. The nut 8 is then tightened until the upper surface of the support washer 23 is flush with the upper edge of the cup member 22. The stack of disc springs 21 is designed and calibrated such that the required force is expressed when the support washer 23 is in this position.

Claims: A valve comprising a valve stem (2) surrounded in part by a packing material (3), and compression means arranged to bring the packing material (3) into sealing engagement with the valve stem (2), the compression means including a spring assembly (21) comprising resilient spring means enclosed within a housing member (22) having a closure member (23) slidably mounted within it, wherein the housing member (22) and closure member (23) are provided with engagement means acting to retain the closure member (23) captive within the housing member (22), and wherein the housing member is a cylindrical cup member (22), characterized in: that the cup member (22) has a base with a central aperture (24) to receive a threaded stud (6) about which the spring assembly (21) fits, that the closure member is a disc-shaped washer (23) with a diameter slightly less than the internal diameter of the housing member (22), wherein the washer (23) has a central aperture to receive the threaded stud (6) about which the spring assembly (21) fits and that the engagement means for retention of the closure member (23) within the housing member (22) comprises inter-engaging formations provided on those two members, wherein the formations are one or more lugs (25, 26) and corresponding longitudinal recesses (27, 28). A valve as claimed in Claim 1, wherein the spring means comprises a stack of annular disc springs (21). A valve as claimed in Claim 2, wherein the diameter of the disc springs (21) is only slightly less than the internal diameter of the housing member (22). A valve as claimed in any preceding claim, wherein the compression means further comprises a sleeve bearing on the packing material (3) and provided with a flange acted on by the spring means. A valve as claimed in any preceding claim, wherein the lug(s) (25, 26) are formed on the closure member and the recess(es) (27, 28) on the internal walls of the housing member. A valve as claimed in any preceding claim, wherein there are provided one pair of lugs (25, 26) and one pair of recesses (27, 28), located at diametrically opposed positions on the closure member and the housing member respectively. A valve as claimed in any preceding claim, wherein the lug(s) (25, 26) are hemispherical. A valve as claimed in any preceding claim, wherein the or each longitudinal recess (27,28) is provided with a by-pass recess (31) intermediate its ends, the by-pass extending from the longitudinal recess (32) to the upper edge of the housing member (22), such that, when removed from the valve, the resilience of the springs (21) will urge the closure member (23) to the upper limit of its travel within the housing member (22) but, by application of suitable downward force and a twisting action, the lugs (25, 26) on the closure member (23) may be transferred into the by-pass recess (31), enabling the closure member (23) to be removed and the assembly disassembled. A valve as claimed in any preceding claim, wherein there are provided stop means limiting the travel of the closure member (23) within the housing member(22).

Inventors: REYNOLDS JAMES ANTHONY, REYNOLDS, JAMES ANTHONY
Applicants: LATTY INT, LATTY INTERNATIONAL S.A.
Application year: 1993
Main classification: F16K41
IPC codes: F16K41, F16J15