BALANCED SOLENOID VALVE

Abstract: A proportional-control solenoid-actuated fluid valve, capable of governing relatively large volumes and rates of flow swiftly and accurately with expenditure of relatively little electrical power, includes a movable valving member (9) positioned by an armature (8,20) having a substantially frictionless spring suspension (15,16), the armature (8,20) being under influence of a special force-counterbalancer in the form of a bellows (18) proportioned and dis­ posed to exert upon it, automatically, neutralizing forces which are substantially equal and opposite to unavoidable pressure-induced imbalances afflicting the valving member (9). The same pressures which tend to unbalance the valve member are impressed upon opposite sides of the bellows (18), one through an enabling bleed port (19), and resulting forces developed by the bellows (18) over a defined area are exerted upon the armature (8, 20) mechanically in a counterbalancing sense.

Description: The invention relates to a fluid valve apparatus comprising a valve body having fluid inlet and outlet ports, a valve seat having a passageway for connecting said ports, a valve element including a valve stem structure fixed with a valving member, solenoid control means for moving and setting the position of said valve stem structure and said valving member along an axis toward and away from said valve seat to govern flow of fluid between said ports through said valve seat passageway, said solenoid control means comprising an electrical solenoid winding and a cooperating relatively movable armature of magnetic material fixed with and movable with said valve stem structure along said axis, yieldable frictionless motion-accomodating seal means comprising a metal bellows connected fluid-tight between said valve element and said valve body and allowing substantially frictionless relative movement therebetween along said axis, and biasing-spring means for exerting force between said valve body and said valve element along said axis in a direction to bias said valving member toward closure with said valve seat. Such a fluid valve apparatus known from the US-A-3 875 612 comprises a solenoid incorporated in a spring biased piston disposed in a pneumatic cylinder. A holding plate of the solenoid is partially undercut so that when the valve is open and the solenoid is deenergized, the fluid pressure acting on the undercut surface and on the valving member abruptly moves the holding plate, the valve stem structure and the valving member toward closure with the valve seat. As soon as the plate separates from the magnet of the solenoid its effective surface area increases, which accelerates the closing. The spring thereafter urges the piston against the holding plate to maintain the valve closed. To open the valve the pressure above the piston is vented and the magnet is energized, which forces the piston, holding plate, stem structure and valving member upwards against the spring force. However, the construction of the known fluid valve apparatus is very complicated as pneumatic means are required for operating the valve element. Further the use of pneumatic pressures makes it difficult to accurately control the flow through the passageway of the valve seat. It is the object of the invention to provide a fluid valve apparatus of uncomplicated construction which accurately controls high volume flows. Starting out from the fluid valve apparatus of the generic kind this object is obtained in that the electrical winding of the solenoid is fixed with said valve body, substantially frictionless means is provided for suspending said valve stem structure in said valve body in support of said valving member for movements thereof along said axis toward and away from said valve seat in nearby positions where fluid pressure differences appear across said valving member and create first net forces tending to move said valving member in one direction along said axis, said substantially frictionless means including at least a pair of flat springs connected between said stem structure and said valve body at axially spaced positions along said axis, the metal bellows is connected fluid-tight between said valve stem structure and the valve body and defines a closed path along which it accomodates said relative movements whose enclosed effective area, transverse to said axis, is about the same as that of said valve seat passageway and the confronting surfaces of said valving member, transverse to said axis, means are provided for exposing those surface areas of said valve stem structure which are transverse to said axis and lie to one side of the seal provided by said motion-accomodating seal means to pressures at said inlet port and for simultaneously exposing those surfaces of said valve stem structure which are transverse to said axis and lie to the other side of said seal provided by said motion-accomodating seal means to pressure at said outlet port, whereby said valve stem structure is subjected to second net forces being related to differences in pressures at said inlet and outlet ports and being of substantially the same magnitude as said first net forces and in direction opposite thereto, and the biasing-spring means is adjustable and provided for exerting force between said valve body and said valve stem structure. The fluid valve apparatus according to the present invention is of uncomplicated construction and can swiftly and accuratel govern even relatively large volumes and high rates of fluid flow using relatively low levels of electrical power, aided by force counterbalancing achieved through use of a bellows-type coupling. Sensitive and precise fluid valving is achieved by way of the frictionless suspension of a broad area valving member and the counterbalancing of undesirable pressure-generated forces through a correlated pressure-responsive coupling. In a preferred embodiment of the fluid valve apparatus according to the present invention said means exposing said surface areas which lie to said one side of said seal includes a fluid bleed passageway in said valve body applying pressures of said inlet port to said surface areas which lie to said one side of said seal, wherein said valving member is disposed on the downstream side of said valve seat, and wherein said biasing-spring means comprises a set-screw member threadedly adjustable in said body along said axis and a spring compressed between said set-screw member and said stem structure and urging closure of said valving member against said seat in the absence of solenoid actuation of said armature by said solenoid winding. Further details as to preferred practices and as to further objects and features of the invention may be most readily comprehended through reference to the following detailed description when taken in connection with the accompanying drawings, wherein: FIG. 1 provides a transverse cross-section of an improved solenoid valve constructed in accordance with the present teachings, certain of the internal components being portrayed in full rather than cross-sectioned; FIG. 2 is a plan view of one of the armature guide springs in the valve of FIG. 1; FIG. 3 is a plan of the second armature guide spring in the valve of FIG. 1; FIG. 4 illustrates a portion of the FIG. 1 valve on a somewhat enlarged scale and in a different operating condition, partly in cross-section; and FIG. 5 depicts relationships between the valve seat and balancing bellows in a valve such as that of FIGS. 1 and 4, together with line work characterizing their effective areas involved in pressure counter-balancing. Having reference to the drawings, wherein like reference characters designate identical or corresponding components and units throughout the several views, and more particularly to FIG. 1 thereof, a precision high-flow-rate valve 6, which is capable of proportional-control valving of large volumes of fluid under influence of only relatively low-power electrical control signals, is shown to include an annular electrical solenoid coil 7 associated with a movable magnetic armature core 8 fixed with a valving member 9 disposed to open and close a flow path through a stationary valve seat 10. A valve body 11 supports and orients the various parts, and includes an upstream inlet port 12 communicating directly with a downstream outlet port 13 solely through the annular seat 10. That separately-fashioned fitted seat is preferably formed with but a narrow upper rim, 10A, against which the elastomeric face pad 9A of valving member 9 may be closed in a fluid-tight sealing relation when the solenoid coil 7 is essentially unenergized. The seat, valving member and armature are aligned collinearly with a vertical axis, 14-14, along which the valving movements take place. Centering and wholly frictionless suspension of the movable valving elements and armature are achieved by a spaced pair of flat springs, 15 and 16, whose outer peripheries are respectively fixed with the armature core 8 and a central valve stem structure 17 extending between the armature core and the valving member 9. Importantly, for a pressure-counterbalancing which essentially isolates this valve from certain deleterious influences of differentials of pressure appearing across upstream and downstream boundaries of the valving member, the valve stem and body are bridged and sealed by an axially-compliant bellows 18 whose interior is exposed to downstream pressures in the valve and whose exterior is exposed to upstream pressures via an accommodating body passageway 19. In a generally-conventional way, electrical excitation of the solenoid coil 7 develops magnetic flux which toroidally encircles it, traversing its axially-centered core 20 and its outer cover 21 and a lower mounting flange 22, all of which are of appropriate magnetic material. However, there is a central air gap 23 which remains unclosed by that magnetic material; it is left between the lower end of solenoid core 20 and the upper end of the aforementioned armature core 8. A non-magnetic (stainless steel) hollow sleeve 24 is welded to and mechanically interconnects the lower end of solenoid core 20 with the mainvalve body 11, and has a sufficiently large central axial opening to just freely accommodate axial movements of armature 8. The latter movements occur in the upward direction, tending to shorten the gap 23, when larger control currents are driven through coil 7 by a suitable source, such as an output amplifier stage of a controller which may be associated with a flowmeter sensing conditions which are to be regulated by valve 6. In its quiescent state, with essentially no net current being driven through its coil, the solenoid does not draw the armature upwardly in a gap-closing action, and, instead, the armature simply tends to rest somewhat neutrally in a lowermost position (illustrated in FIG. 1) at which the interconnected valving member 9 engages and seals itself upon the seat 10 to block flow between inlet 12 and outlet 13. Stable centering and frictionless suspension of the armature and valving member by the two flat springs 15 and 16 preferably involves a wide spacing of them, and, accordingly, the thin flat spiral unit 15 (FIG. 2) is fitted between the top of the armature 8 and interior of the stainless steel sleeve 24 (FIG. 1), while the triple-arm spider unit 16 (FIG. 3) is fitted between a lower portion, 17B, of the valve stem structure and the surrounding body (FIG. 1). To ensure that firm fluid-tight closure of the valve will occur under zero-excitation conditions, a light controllable downward bias force is provided by a small helical spring 25 which is adjustably compressible and settable by an associated set screw 26 threadedly fitted within the accommodating hollow interior of central solenoid core member 20. That spring 25, exerts the controlled and regular bias force between the set screw and the top of the movable armature core 8. Even though the closure-biasing force applied by set spring 25 is only quite small, and even though there is a relatively large area of the face 9A of the valving member 9 which may be exposed to high upstream pressure in inlet port 12, the improved valve does not become forced open unintentionally. That is so because of continual automatic application of counteracting forces which are applied in amounts just equal to the imbalance force which would otherwise exist due to fluid pressure effects. Therefore, essentially only the small bias of spring 25 and relatively small spring restraints of the centering springs 15 and 16 need to be overcome when control currents in the solenoid dictate that the valving member be lifted from its seat to varying extents for swift control of different amounts of fluid flow. Although flexible bellows 18 will nevertheless resist stretching and compressing to some degree, the forces involved are virtually negligible, particularly where, as shown, there are many thin and axially-compliant folds or convolutions stacked together. Moreover, the bellows ribs which so conveniently yield well axially also advantageously tend to be highly rigid radially and can therefore withstand net fluid pressures acting in those spurious directions. Importantly, the bellows is securely sealed both mechanically and fluid-tight, as by welding, around its upper end, with an upper valve stem portion 17A, and around its lower end, with the cooperating sleeve member 11A inserted into and sealed with the valve body as a part thereof. On its interior, bellows 18 always witnesses whatever pressures exist downstream of valving member 9, the same as those at fluid outlet port 13. However, on its exterior surfaces, the pressures always witnessed are the same as those at the upstream inlet port 12, because such pressures are coupled between those sites by the body passageway 19. The various illustrated O-ring seals ensure that there is no leakage of the controlled fluid and that the aforesaid differences in pressures will be experienced by the bellows. A somewhat exaggerated opened condition of the valve is represented in FIG. 4, and it should be understood that only a very small axial motion and maximum seat clearance is required to achieve full opening and a high flow volume with the relatively large-area seat passage and valving member involved in such a valve. Typically, a maximum span of only about fifteen thousandths of an inch of motion need occur, and that small order of displacements ensures that the suspension springs 15 and 16 can exert little restraint and that bellows 18 will neither be overstressed nor add any noticeable unwanted forces. Dashed linework 28 in FIG. 5 characterizes the circular outline about which relative axial motion via the bellows is effective. It lies between the radially inner and outer reaches of the convolutions or ribs 18A, and, for greatest accuracy, may be determined empirically with bellows of different origins, materials and constructions. As is indicated by the further dashed linework 27, the region for relative motion established by the bellows is selected to have about the same limits as the passageway of seat 10, which then ensures that the upward forces which are the products of seat area times inlet pressure will be counterbalanced by downward forces which are products of the same inlet pressure times the like effective area established by the bellows. Even when the valve is opened and fluid flows, the valving member tends to experience different pressures above and below it, which would result in unwanted net forces unless counterbalancing also occured; but, such counterbalancing does always take place with aid of the bellows, which likewise experiences substantially the same different pressures and thus occasions the needed equal and opposite counteracting forces. In other constructions the valving or plug members, and cooperating seats, may have configurations specifically different from what has been illustrated, and the counterbalance bellows may therefore not have a like outline while yet offering the needed force offset and related advantages. Also, bellowframe-type or diaphragm-type frictionless counterbalance couplings may in some cases be able to contribute useful compensations.

Claims: 1. Fluid valve apparatus comprising a valve body (11) having fluid inlet (12) and outlet (13) ports; a valve seat (10) having a passageway for connecting said ports (12, 13); a valve element including a valve stem structure (17) fixed with a valving member (9); solenoid control means for moving and setting the position of said valve stem structure (17) and said valving member (9) along an axis (14) toward and away from said valve seat (10) to govern flow of fluid between said ports (12, 13) through said valve seat passageway, said solenoid control means comprising an electrical solenoid winding (7) and a cooperating relatively movable armature (8, 20) of magnetic material fixed with and movable with said valve stem structure (17) along said axis (14); and yieldable frictionless motion-accomodating seal means comprising a metal bellows (18) connected fluid-tight between said valve element and said valve body (11) and allowing substantially frictionless relative movement therebetween along said axis (14); and biasing-spring means (25, 26) for exerting force between said valve body (11) and said valve element along said axis (14) in a direction to bias said valving member (9) toward closure with said valve seat (10) characterised in that the electrical solenoid winding (7) is fixed with said valve body (11), substantially frictionless means is provided for suspending said stem structure (17) in said valve body (11) in support of said valving member (9) for movements thereof along said axis (14) toward and away from said valve seat (10) in nearby positions where fluid pressure differences appear across said valving member (9) and create first net forces tending to move said valving member (9) in one direction along said axis (14), said substantially frictionless means including at least a pair of flat springs (15, 16) connected between said stem structure (17) and said valve body (11) at axially spaced positions along said axis (14); the metal bellows (18) is connected fluid-tight between said valve stem structure (17) and the valve body (11) and defines a closed path along which it accomodates said relative movements whose enclosed effective area, transverse to said axis (14), is about the same as that of said valve seat passageway and the confronting surfaces of said valving member (9), transverse to said axis (14); means are provided for exposing those surface areas of said valve stem structure (17) which are transverse to said axis (14) and lie to one side of the seal provided by said motion-accomodating seal means to pressures at said inlet port (12) and for simultaneously exposing those surfaces of said valve stem structure (17) which are transverse to said axis (14) and lie to the other side of said seal provided by said motion-accomodating seal means to pressure at said outlet port (13), whereby said valve stem structure (17) is subjected to second net forces being related to differences in pressures at said inlet and outlet ports (12, 13) and being of substantially the same magnitude as said first net forces and in direction opposite thereto; and the biasing-spring means (25, 26) is adjustable and provided for exerting force between said valve body (11) and said valve stem structure (17). 2. Apparatus according to claim 1, characterised in that said means exposing said surface areas which lie to said one side of said seal (18) includes a fluid bleed passageway (19) in said valve body (11) applying pressures of said inlet port (12) to said surface areas which lie to said one side of said seal (18), wherein said valving member (9) is disposed on the downstream side of said valve seat (10), and wherein said biasing-spring means comprises a set-screw member (26) threadedly adjustable in said body (11) along said axis (14) and a spring (25) compressed between said set-screw member (26) and said stem structure (17) and urging closure of said valving member (9) against said seat (10) in the absence of solenoid actuation of said armature (8, 20) by said solenoid winding (7).

Inventors: EWING, JAMES H.
Applicants: MKS INSTRUMENTS, INC.
Application year: 1988
Main classification: F16K31
IPC codes: F16K31