FLUID-FLOW CONTROL VALVE

Abstract: A flow limit valve for limiting the flow rate of a pressurized fluid includes a valve body (9) with an intercon­ necting cavity (23) of circular cross section. Within the cavity is a piston (21) that slides within the cavity under force generated by a pressure differential across the piston to a closed position which prevents fluid flow through the valve. A pin (49) is provided that is attached to the piston (31) and that protrudes through the piston seat (29) into the outlet side of the cavity when the piston is at the closed position. Opposite the pin (49) is an encapsulated magnet (45) within the valve body (9) that can be moved in response to another magnet (75) outside the valve body to contact the pin (49) attached to the piston (31) to move it to the open position. The magnetic forces applied through the valve body affect internal valve operation via the pin (49) attached to the piston (31) and this avoids the danger of noxious fluids escaping through sliding seals or flexible membranes.

Description: The present invention relates to valves for controlling the flow of pressurized fluids and more specifically to flow limit valves that close when the flow rate exceeds a limiting value. Flow limit valves are commonly used as safety devices in pressurized fluid distribution systems to isolate fluid sources from any ruptures or breaches to minimize the loss of pressurized fluids. Properly designed systems using pressurized gases or liquids that are toxic, corrosive, or explosive employ flow limit valves to minimize exposure to these hazardous chemicals in accident situations. Water distribution systems often utilize flow limit valves to prevent excessive water loss due to pipe breakage. US-A-4178958 describes a flow limit valve of the kind adapted to close when the flow rate exceeds a limiting value, and comprising a body having an aperture between first and second chambers, the aperture being surrounded by a sealing face at the side of the aperture facing the first chamber, which chambers communicate respectively with a fluid inlet and a fluid outlet, an element disposed within the first chamber for movement towards a closed position in sealing engagement with the sealing face but biassed in a direction away therefrom said element defining restricted passage means from the inlet to the aperture, the cross-sectional area of the fluid passage means being selected so that fluid flow therethrough imparts a flow-dependent self-actuated moving force to the element to move the latter into sealing engagement with the sealing face in response to a selected flow rate through said passage means, and control means for engaging an actuator which projects through the aperture from the element in the closed position to unseat the element from the sealing face. Functionally, a flow limit valve permits fluid flow up to a predetermined limiting flow rate. The flow rate through a device is proportional to the difference between the upstream supply pressure and the downsteam outlet pressure. During normal operation, the pressure differential across the valve establishes a flow rate through the valve that is less than or equal to the limiting flow rate. A rupture in the downstream distribution system causes a reduction in the downstream pressure and, hence, an increase in the pressure differential across the valve. This increased pressure differential corresponds to a flow rate through the valve which may exceed the limiting flow rate. To limit the flow rate through the flow limit valve to the predetermined limit, the said element acts like a piston or similar device which moves against the force of a biassing spring to block the flow path when the pressure differential exceeds that which corresponds to the limiting flow rate. All flow through the valve is blocked until the pressure differential is lowered by repairing the rupture and the piston element is reset to its original position manually. Another typical flow limit valve in the prior art includes a primary flow path through an orifice from an inlet port to an outlet port. A movable piston is provided to close the primary flow path when the pressure differential across the orifice exceeds a certain value. Fluid from the inlet and outlet sides of the orifice is ported to opposite sides of the piston. The outlet pressure, assisted by a spring, tends to move the piston to an open position, which permits fluid to flow through the valve, and the inlet pressure tends to move the piston to a closed position, which prevents fluid flow. The spring and the piston are designed such that any pressure differential greater than the pressure differential that corresponds to the limiting flow rate allows the inlet pressure to overcome the outlet pressure and the spring force to move the piston to the closed position. To reset this flow limit valve, a bypass valve is opened and fluid flows through a secondary flow path to equalize the pressure on each side of the piston thereby allowing the spring to move the piston to the open position. Certain known valves use a third flow path with an integrated valve to bypass the shut-off piston for providing adjustment of the flow limit. Flow limit valves of these types are expensive to manufacture and difficult to purge due to the multiple flow paths and bypass valves involved. Also, the flow rate through a flow limited valve should be proportional to the pressure differential up to the limiting value of the flow rate and should sharply fall to zero when the limiting value is exceeded. However, spring-biased flow limit valves allow a flow rate that is proportional to the pressure differential up to the point where the piston begins to compress the spring and move from the open position to the closed position, but do not provide a sharp closure because of the additional pressure differential necessary to further compress the spring and complete the movement of the piston from the open position to the closed position. Further, known valves for controlling the flow of toxic or corrosive fluids and gases commonly rely upon flexible members or sliding seals to control operation or reset of the valve from the environment, as shown for example in US-A-4178958. However, such schemes are generally unsatisfactory because of the danger that the environment may become contaminated by the noxious fluid flowing through the valve if the flexible member or sliding seal fails under fluid pressure. In addition, a flexible member such as a bellows-type or diaphragm-type device or a sliding seal commonly introduces anomalous "pockets" or chambers along the passages for fluids which are difficult to purge of residual fluid when the fluid system has to be cleaned, or a new fluid which must not be contaminated by residual fluid is to be introduced. What is needed, therefore, is a flow limit valve which is low cost and which provides for a sharp valve closure at a limiting flow rate. What is additionally needed is a flow limit valve which is convenient to reset to an open position and which may be adapted to different limiting flow rates. Also, such a valve should have minimal "pockets" for easy purging and should obviate the dangers of leaking noxious fluids into the environment through sliding seals. The invention aims to remedy the above-mentioned drawbacks inherent in the fluid-flow control valves. DE-U-1961838 describes a non-return valve which can be unseated by using magnetic attraction between aligned magnets. US-A-3877478 describes a fluid flow control valve which is controllably opened by magnetic repulsion between aligned magnets. In accordance with this invention a flow limit valve of the above described kind is characterized in that the first chamber is below the second chamber and the element is free floating in the first chamber, its direction of movement being substantially vertical, whereby the weight of the element biasses it away from the sealing face, and in that the control means comprises a magnet disposed within the second chamber and biassed by a spring upwardly away from the actuator and magnet means are disposed outside the body to interact in direct alignment with and in magnetic repulsion with the magnet of the control means for moving the latter against the spring and thereby to unseat the element. In accordance with a preferred embodiment of this invention, the flow limit valve includes a valve body with threaded or welded glands at the inlet and outlet ports and an interconnecting cavity of circular cross section. Within the cavity is a guide housing defining the first lower chamber and guiding a piston element with passageways which determine the limiting flow rate of the valve and which establish a pressure differential across the piston element as a result of fluid flow therethrough. The flow path of fluid through the valve is from the inlet port to the inlet side of the first chamber, along sides of the piston element into the outlet side of the first chamber and then through said aperture and said second chamber to the outlet port. If the force generated by the pressure differential across the piston exceeds the force necessary to lift the mass or weight of the piston, then the piston slides within the first chamber to a closed position which prevents fluid flow through the valve. An integral elastomeric pad on the piston forms a seal to shut off the flow path when the piston is at the closed position. The actuator comprises a pin which is attached to the piston and which protrudes through the aperture into the second chamber when the piston is at the closed position. In one embodiment, an encapsulated magnet is disposed in the second chamber to contact the pin and move the pin and the attached piston to the open position. Thus, improved means are provided for valving noxious fluids which include magnetic actuators that coact through an improved design of solid valve body to assure integrity against leaks and permit substantially complete purging of residual fluids. An advantage of the present invention is the sharp transition from a flowing to a blocking state. A further advantage of the present invention is the ease of resetting the valve from the blocking to the flowing state without relying upon the integrity of bellows or diaphragms or sliding seals. Still another advantage of the present invention is the ease of changing the flow rate limit by changing the internal piston with its associated parameters of weight and cross section of fluid passageways. The invention is further described with reference to the accompanying drawings, in which:- Fig.1 is a sectional view of the valve according to the present invention; Fig.2 is a sectional view of another embodiment of the valve of Fig.1. Referring to Figure 1, a flow limit valve of the present invention, which limits the flow of a pressurized fluid to a selected limit, has a hollow, substantially cylindrical valve body 9 having laterally-positioned inflow and outflow passages 11 and 13. The lower end 15 of the valve body 9 is closed off by a plug 7 which is theaded or otherwise removably attached to the valve body 9. An elastomeric seal 19 is compressed between the plug 7 and valve body 9 to form a seal to prevent fluids within the structure from leaking into the environment. The plug 7 is of sufficient diameter to provide access, when removed, to the internal parts of the valve for assembly and repair. The internal parts include a guide housing 21 which is positioned within the internal bore 23 of the valve body 9 against a shoulder 8 and which has an aperture 28 surrounded by a valve seat 29. The guide housing 21 defines a first chamber 36 in which is guided a piston 31. A seal ring 27 is positioned between the valve body 9 and the housing 21 to prevent fluid leaking past the valve seat 29 when it is closed off by an elastomeric seat 33 on the piston 31. The piston 31 has longitudinal grooves or flats formed in its cylindrical surface to provide fluid passages 6 of selected cross-sectional area for fluid to flow from the inflow passage 11 via connecting ducts 35 and 37. Above, or "downsteam" of, the piston 31, valve seat 29 and aperture 28 is an upper or second chamber 39 which is connected to the outflow passage 13 via duct 71. A flat spring 43 is located within the upper chamber 39 between the top of the housing 21 and the base of a magnet 45 which may be encapsulated within a stainless steel housing or casing or encapsulated in fluid-impervious material,such as polypropylene or polytetrafluoroethylene ("TEFLON" material available from DuPont Co.). The encapsulated magnet 45 is disposed to slide within the upper chamber 39 so that its lower face 47 contacts a pin 49 that is carried by the piston 31 to protrude through the valve seat 29 for resetting purposes, later described. An upper housing 51 is suitably attached to the top of valve body 9 (e. g., by threaded attachment or by set screw 73, or the like) to confine the movement of another magnet 75 in a direction aligned with the magnet 45 inside the valve body. Both magnets are oriented for magnetic repulsion, and the upper magnet may be encased in bright-colour anodized aluminium 53 to identify the protruding magnet as a button for resetting purposes, later described. The valve body 9 is preferably formed of non-magnetic (or low-level magnetic) material such as brass, stainless steel, aluminium, plastic, or the like, to permit suitable interaction between magnets. In operation, the valve of the present invention is oriented substantially vertically, as shown, and the flat spring 43 supports both magnet 45 and the repelled magnet 75. The piston 31 is normally down in the internal base of the housing 21, thus leaving the valve seat 29 and elastomeric seat 33 clear or open for fluid flow therethrough. Note that fluid entering the inflow passage 11 normally flows through ducts 35,37 and passages 6, through the valve seat 29,33 to the upper chamber and then via chamber 39 and duct 71 to the outflow passage 13. The weight of piston 31 and the cross section of the longitudinal grooves or flats 6 in the walls of piston 31 determine, for a certain density of fluid, the limit of fluid flow rate past the piston 31 before the piston is moved up to close off the flow at valve seat 29 and elastomeric seat 33. The piston 31 in the illustrated embodiment thus operates both as the metering device and as the shut-off device. A substantial pressure differential can exist across the valve seats 29,33 to maintain the piston in sealing position against the valve seat. Thus, flow of a fluid in excess of a selected amount moves the piston 31 to shut off the flow. Pistons of different weight and having differently-sized passages 6 may be inserted into the housing 21, following removal of plug 7, to establish different upper limits of fluid flow at which the piston 31 moves to seal off the flow. A range of maximum values of fluid flow can readily be determined simply by changing pistons 31 (i. e., with different weights and grooves) to cover fractional litres per minute up to hundreds of litres per minute, at selected static pressure, for most applications in which noxious fluids must be controlled. If excess flow of fluid occurs and the piston 31 moves up to seal off further flow, the valve will not reset itself as long as static pressure is maintained at the inflow side of the valve. Therefore, the valve must be reset to position the piston 31 away from the valve seat 29. This is accomplished from the environment without sliding seals or bellows, or the like, by action of pin 49 that protrudes loosely through the aperture 28 in the valve seat 29 for mating engagement with face 47 on magnet 45. Thus, the upper magnet 75 is depressed to decrease the spacing between magnets and thereby to increase the repulsion force imparted downwardly on magnet 45. When the repulsion force overcomes the upward force imparted by spring 43 on magnet 45, the face 47 engages pin 49 and moves it and piston 31 downwardly away from the valve seat 29 to restore fluid flow again. The surface area of valve seat 29 may be selected in inverse relationship to the operating fluid pressure to provide valves for operation in pressure ranges from about 0,145 - 435 kPa (1 - 3000 psi). In accordance with another embodiment of the present invention, as illustrated in Fig. 2, the resetting operation of the basic valve assembly is remotely controlled by an actuator 77 which includes the upper magnet 75 contained within a pneumatic (or electromagnetic) structure. In this embodiment, the upper magnet 75 is included within a piston 79 which is slidably mounted within the housing 81 that has a fluid port 83 formed at the upper end. Thus, by applying fluid under pressure to the port 83, the piston 79 moves magnet 75 closer to magnet 45 and thus resets the piston 31 in the manner as previously described. The spring 65 returns the upper magnet 75 to the topmost position after fluid pressure at port 83 is reduced. Of course, the actuator 77 may also be electromagnetic in nature simply by forming a solenoid in cylindrical alignment with magnet 75 so that, upon application thereto of electric current, the resulting magnetic field will interact with magnet 75 in known manner to move it closer to magnet 45 for reset operation in the manner as previously described. The inflow and outflow passages 11,13 in each embodiment may be welded to the valve body 9, and the entire structure may be contained within approximately 31.75mm (1-1/4") diameter and 63.5mm (2-1/2") height for compact, reliable operation. Purging of the structure to remove residual fluid is simplified in each embodiment by the reduced size and small internal volume, and by the substantially smooth flow-through design of the internal fluid passage which eliminates the need for multiple passageways, as previously described. Therefore, the valve structure of the present invention contains noxious fluids within a sealed structure that does not rely upon sliding seals or flexible members to provide controlling motions applied from the environment. In addition, the entire structure can be assembled and serviced through a sealable port so that, once assembled, the maximum flow setting at which automatic shut-off occurs in one embodiment cannot be tampered with. Also, simple modifications enable the basic valve structure to be operated in different manner consistent with requirements for remote control of on-off operation or of reset function of automatic shut-off operation.

Claims: A flow limit valve adapted to close when the flow rate exceeds a limiting value, comprising a body (9,21) having an aperture (28) between first and second chambers (36,39), the aperture (28) being surrounded by a sealing face (29) at the side of the aperture (28) facing the first chamber (36), which chambers (36,39) communicate respectively with a fluid inlet (11) and a fluid outlet (13), an element (31) disposed within the first chamber (36) for movement towards a closed position in sealing engagement with the sealing face (29) but biassed in a direction away therefrom, said element (31) defining restricted passage means (6) from the inlet (11) to the aperture (28), the cross-sectional area of the fluid passage means (6) being selected so that fluid flow therethrough imparts a flow-dependent self-actuated moving force to the element (31) to move the latter into sealing engagement with the sealing face (29) in response to a selected flow rate through said passage means (6), and control means (45) for engaging an actuator (49) which projects through the aperture (28) from the element (31), in the closed position to unseat the element (31) from the sealing face (29), characterised in that the first chamber (36) is below the second chamber (39) and the element (31) is free floating in the first chamber (36), its direction of movement being substantially vertical, whereby the weight of the element (31) biasses it away from the sealing face (29), and in that the control means comprises a magnet (45) disposed within the second chamber (39) and biassed by a spring (43) upwardly away from the actuator (49) and magnet means (75) are disposed outside the body (9,21) to interact in direct alignment with and in magnetic repulsion with the magnet (45) of the control means for moving the latter against the spring (43) and thereby to unseat the element (31). A flow limit valve according to claim 1, in which said magnet means (75) is mounted for vertical movement in response to a manually applied force. A flow limit valve according to claim 1 or 2, in which said magnet means (75) comprises a permanent magnet.

Inventors: EIDSMORE, PAUL G.
Applicants: EIDSMORE, PAUL GEORGE
Application year: 1985
Main classification: F16K31
IPC codes: F16K17, F16K31