Diaphragm-sealed valve having intermediate communication ports

A diaphragm-sealed valve having communication mechanisms operatively connecting neighboring pairs of grooves is provided. Each communication mechanism has a communication port opening in an interface of a valve cap, between the neighboring grooves. The communication mechanism also has a communication conduit extending within the valve cap and connecting the communication port and one of the neighboring grooves. It also has a recess within a valve body aligned with the communication port and with the other one of the neighboring grooves, a flexible sealing surface of the diaphragm being seated within the recess and resiliently biased away from the interface of the valve cap. A plunger assembly is also provided, including plungers movable to push flexible sealing surface towards the communication port.

FIELD OF THE INVENTION

The present invention generally relates to fluid analytical systems and more particularly concerns a diaphragm-sealed valve having improved characteristics for use in such systems.

BACKGROUND OF THE INVENTION

As well known by people involved in the art, chromatographic systems rely on the use of valves to allow reproducible sample introduction and various column switching schemes.

For the last forty years, many people have designed diaphragm valves for chromatography. Such diaphragm valves have been used in many commercially available gas chromatographs. They are apt to be integrated more easily in a gas chromatograph due to their physical size and since the actuator is embedded in the valve itself. These characteristics make them attractive for gas chromatograph manufacturers.

Referring toFIG. 1(PRIOR ART), there is shown an example of a typical diaphragm-sealed valve as known in the art. The valve1is provided with a top block2having an interface4and a plurality of ports6. Each of the ports6opens at the interface4and has an inclined thread passage8to connect various analytical fitting and tubing (not shown). At the bottom of the inclined thread passage8, there is a conduit10extending in the top block2and opening at the interface4. The ports6are arranged on a circular line on the interface4of the top block2. The interface4is advantageously flat and polished to minimize leaks between ports and from the ambient atmosphere. The valve1is also provided with a bottom block12and a diaphragm14, which is generally made of polyimide, Teflon or other polymer material. The diaphragm14is positioned between the top block interface4and the bottom block12, and has a recess therein extending along the circular line formed by the ports6and biased away from the interface4of the top block2. The recess18in the diaphragm14sits in a matching recess20made in the bottom block12, thereby allowing some clearance for fluid circulation between adjacent ports6.

The valve1is also provided with a plurality of plungers16mounted in the bottom block12, each being respectively arranged to be able to compress the diaphragm14against the top block2at a position located between two of the ports6. Preferably, as illustrated, when the valve is at rest, three plungers16are up while the other three are down. When the plungers are up, they compress the diaphragm14against the top block2and close the conduits made by the diaphragm recess18, so that fluid circulation is blocked. The bottom block12keeps the plungers16and the actuating mechanism in position.

The performance of valves of the type shown inFIG. 1is generally poor. The leak rate from port to port is too high for most applications and thus limits the system performance. Moreover, the pressure drop on the valve's ports differs from port to port, causing pressure and flow variations in the system. This causes detrimental effects on column performance and detector baseline. Furthermore, many valve designs allow for unacceptable inboard contamination.

As explained above, in the valve ofFIG. 1, the sealing of the fluid circulation path between two ports6relies simply on the surface of the plunger defining the area that presses the diaphragm recess18on the interface4. This technique imposes tight restrictions on the surface finish and flatness, and on the length of the plungers. Any scratch on the interface4or imperfection of the diaphragm14will generate leaks. Moreover, the length of all plungers must be the same. Any difference in their lengths will result in leaks, since a shorter plunger will not properly compress the diaphragm against the interface4.

Several variations of the general concept of the valve ofFIG. 1are known in the art. The main differences relate to the location of the bottom block recess20. In the past, this recess20or its equivalent was located internally in the top block2, or on its interface4. U.S. Pat. Nos. 3,111,849; 3,198,018; 3,545,491; 3,633,426 and 4,112,766, which were granted to the same inventors, illustrate valves provided with such recesses. However, as reported in a more recent valve brochure specification entitled “Applied Automation Company, series 11 diaphragm valve” (now commercialized by Siemens), this method is no longer used because of a too high cold flow. Cold flow is also often referred to as cross port flow leak. The latest design from the same group, which was commercialized, uses a flat and polished interface4on the top block2and a recess20in the bottom block12. In this design, the diaphragm14has no recess. Moreover, in order to reduce the cold flow, it was also envisaged to use two diaphragms. U.S. Pat. No. 3,111,849 teaches the use of a “cushion” diaphragm to allegedly compensate for any slight non-parallelism or length difference of plungers. Other attempts have also been made to correct the non-parallelism, as disclosed in U.S. Pat. Nos. 3,376,894; 3,545,491 and 3,633,426, wherein the use of solid plungers has been replaced with the use of small steel balls.

The above-mentioned concern about plunger length has also been taken into consideration in U.S. Pat. No. 6,202,698, granted to Valco Company, which suggests the use of plungers made of softer material. This allows tolerance reduction for the length of such plungers. However, such a design will still result in an important leak rate between ports since the pressure from the plungers is not equal on the diaphragm.

Other attempts have been made in the past to eliminate problems caused by plunger tolerance variations. U.S. Pat. No. 3,139,755 discloses a valve devoid of plungers, hydraulic pressure being used instead. However, an auxiliary source of pressure must be used, since no pneumatic amplification of the pneumatic actuating mechanism is performed. Another design is disclosed in U.S. Pat. No. 3,085,440. In this valve, the diaphragm has been replaced by an O-ring.

In brief, in view of the previously mentioned patents, it can be seen that many attempts have been made to fix cross port leaks problems and outboard or inboard contamination. All of the proposed designs are quite similar with regard to sealing mechanisms, and have the same drawbacks.

There is therefore a need for an improved diaphragm-sealed valve.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, there is provided a diaphragm-sealed valve that includes a valve cap having a first interface and a plurality of grooves extending in the first interface. The valve cap further includes a plurality of process conduits extending therethrough, each process conduit ending in a process port opening on a corresponding one of the grooves. The valve also includes a valve body having a second interface which faces the first interface of the valve cap. The valve body has a plurality of passages extending transversally therein and a plunger assembly including a plurality of plungers. Each of the plungers is placed in one of the passages and is slideable therein between a closed position, where the plunger projects towards the first interface, and an open position, where the plunger is retracted within the valve body. The valve also includes a diaphragm compressibly positioned between the first and the second interfaces.

The valve also includes at least one communication mechanism each operatively connects a neighbouring pair of grooves. Each communication mechanism includes a communication port opening in the first interface between the grooves of the corresponding pair, a communication conduit extending within the valve cap and connecting the communication port and a first one of the grooves of the pair, a recess within the second interface connected to a corresponding one of the passages and aligned with the communication port and with a second one of the grooves of the pair, and a flexible sealing surface integral to the diaphragm and resiliently biased away from the first interface. The flexible sealing surface is seated within the recess of the second interface when the plunger placed within the corresponding passage is in the open position, the flexible sealing surface sealingly closing the communication port when the plunger is in the closed position.

In accordance with a second aspect of the present invention, there is also provided a valve including a valve cap having a first interface and a plurality of grooves extending in the first interface. The valve cap further includes a plurality of process conduits extending therethrough, each process conduit ending in a process port opening on a corresponding one of the grooves.

The valve also includes a valve body having a second interface facing the first interface of the valve cap. The valve body further has a plurality of passages extending transversally therein, and a plunger assembly. The plunger assembly includes the following components:a plurality of plungers each mounted in one of the passages and being slideable therein between a closed position, where the plunger projects towards the first interface, and an opened position, where the plunger is retracted within the valve body. Each plunger is either a normally closed plunger or a normally open plunger;a push plate extending within the valve body in parallel to the second interface and movable transversally thereto. The normally closed plungers are mounted on this push plate. A plurality of cavities extend through the push plate for allowing the normally open plungers therethrough;an upper piston extending under the push plate contiguously thereto, the normally opened plungers being mounted thereon;a lower piston extending under the upper piston contiguously thereto, the lower piston being rigidly connected to the push plate;biasing means for upwardly biasing the lower piston and downwardly biasing the upper piston; andan actuating mechanism for actuating the plungers between the opened and closed positions thereof. The actuating mechanism controls a distance between the upper and lower pistons.

The valve further includes a diaphragm compressibly positioned between the first and second interfaces, and at least one communication mechanism, each operatively connecting a neighbouring pair of the grooves for allowing fluid communication therebetween.

While the invention will be described in conjunction with example embodiments, it will be understood that it is not intended to limit the scope of the invention to such embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included as defined by the present application.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the following description, similar features in the drawings have been given similar reference numerals. To preserve the clarity of the drawings, some references numerals have been omitted, if they were already identified in a preceding figure.

Referring toFIGS. 2 and 3B, there is shown a valve30according to a preferred embodiment of the present invention.

The valve30is of the diaphragm-sealed type, also referred to in the field as a diaphragm based tight shut off valve. Such a valve may be used in analytical equipments of various types, and more particularly chromatographic equipments or online analyzers.

Referring more particularly toFIG. 2, the valve30generally includes three main components: a valve cap32, a valve body34and a diaphragm84compressibly positioned therebetween. The diaphragm84can be made of multiple layers of polymer, with or without a thin metallic layer, or alternatively be made of metal only. Metals that may be used are stainless steel 316, aluminum, chrome-nickel alloy, copper and the like. For applications requiring high gas-tightness sealing, a diaphragm made of multiple layers of polymer is preferably used, while other applications require a thin metallic layer over the polymer layers. Still referring toFIG. 2, at least one communication mechanism is further provided, as will be discussed in detail below.

FIG. 3Ashows a bottom view of the valve cap32, having a smooth surface defining a first interface36. In this embodiment, the valve cap32of the valve30is cylindrical and is made of electro-polished stainless steel. A thin layer of polymer may preferably cover the first interface36of the valve cap32. Of course, other materials, for example ceramic or various types of polymers, can be used for the valve cap. Shapes other than a cylindrical one may also be considered.

A plurality of grooves40, in this particular case six (6), extends in the first interface36. Throughout the present description, “groove” is understood to mean a channel or a depression formed in the surface defining the first interface36, of a depth appropriate to allow fluid circulation therein. As shown inFIG. 3A, the grooves40are preferably arc-shaped or kidney-shaped, and have first42and second44ends of rounded form. A corresponding process port46opens in each groove40. Throughout the present description, a “port” refers to an opening for intake or exhaust of a fluid. Preferably, each process port46is located closer to the first end42of the groove than to the second end44. In the illustrated embodiment, the grooves are circularly arranged, but they could be placed differently in other embodiments, for example linearly or elliptically. The number of process ports and corresponding grooves may also differ. For example, other embodiments may have 2, 4, 8 or 10 process ports46.

Referring toFIGS. 6 and 6D, each process port46is linked to a process conduit48through which sample or carrier fluids are injected or exhausted, as well known in the art. Each process conduit48preferably has a narrow cylindrical shape and is connected to valve tubings at one of its ends, while the other end terminates in the corresponding process port46. The process conduit48may alternatively have another shape and may incorporate any appropriate feature known in the art.

Referring toFIGS. 7 and 8, the valve body34is shown to have a surface defining a second interface38, which in operation faces the first interface36of the valve cap32. Preferably, the valve body34has a cross section of similar dimensions than the valve cap32. The valve body34has a plurality of passages76extending transversally therethrough. Proximate the second interface38, each passage76has the shape of a cylinder having one extremity opening at the second interface38in a recess78, the diameter of the recess78being larger than the diameter of the corresponding passage76. The valve body34also includes a plunger assembly including a plurality of plungers82, each mounted in a corresponding passage76. Each plunger82is slideable between a closed and an open position.FIG. 7shows a plunger82retracted within the valve body34, defining the open position according to an embodiment of the invention.FIG. 8shows the plunger82of the same embodiment in the closed position where it projects towards the first interface36.

Referring toFIG. 4, a portion of a plunger assembly80is illustrated according to an embodiment of the invention. More particularly,FIG. 4shows two (2) of the (6) plungers82of the embodiment ofFIG. 2. The term “plunger” is understood to mean a mechanism component driven by or against a mechanical force or fluid pressure. As mentioned above, each plunger82is slideable in a corresponding passage76of the valve body34. The diameter of a passage76is slightly larger than that of its corresponding plunger82. Preferably, a guide sleeve81surrounds the passage, for facilitating the movement of the plunger into the passage. The left side plunger ofFIG. 4is shown in the closed position, whereas the right side plunger is shown in the open position.

Preferably, when in the closed position, the contact area of each plunger82is pushed evenly throughout its surface. Thus, all mechanic or fluid forces are transferred equally onto the diaphragm84This design ensures that the plungers82remain substantially vertical when actuated.

According to embodiments of the invention, the plungers are preferably of two types, designated as “normally closed” (nc) and “normally open” (no). In typical chromatography applications, the plungers of a given type are actuated together, so that they are either all in the closed position or all in the open position. As their names indicate, the nc plungers are biased towards the closed position, whereas the no plungers are biased towards the open position.

The plungers82may be actuated by an actuating mechanism. An example of an actuating mechanism is shown with reference toFIGS. 4,4A,4B and5. In the illustrated embodiment, it can be seen that the normally closed plungers82nchave a length different than the length of the normally open plunger82no. A push plate92extends within the valve body34in parallel to the second interface36, and is movable transversally thereto. The normally closed plungers82ncare mounted on this push plate92. An upper piston94extends contiguously under the push plate92. The normally open plungers82noare mounted on the upper piston94. A plurality of cavities93extend across the push plate92for allowing the normally open plungers therethrough. In the illustrated embodiment, the plungers82are affixed to either the push plate92or the upper piston94through a fixed fastener such as screws86, which advantageously allows the valve to be fully operational regardless of its orientation. It will therefore be understood by one skilled in the part that the reference to the directions “up” and “down” throughout the present application is used for ease of reference to the drawings, particularlyFIGS. 4 through 6D, and is not meant to indicate a preferred orientation of the valve in use.

A lower piston90extends contiguously under the upper piston94and is rigidly connected to the push plate. The lower piston90and push plate92therefore move together within the valve body34. Dowel pins91may be provided to prevent the upper94and lower90pistons from rotating with respect to each other, and O-rings89are preferably provided to properly seal the upper94and lower90pistons. (seeFIGS. 6 and 6A).

The lower piston90, push plate92and the normally closed plungers82ncthereon are biased upward by appropriate means. In the illustrated embodiment, a Belleville assembly95, including a Belleville washer stack96and a plate97, cooperates with the lower piston90. The upward force on the Belleville assembly95is controlled by a compression set screw98. The lower piston90therefore pushes the plunger push plate92and keeps the normally closed plunger82ncin the closed position when no opposite force is applied thereon. A bottom cap104closes the valve at its bottom end. Of course, the Belleville washer96may be replaced by any other biasing means, such as standard springs or polymer bushings.

The upper piston94is for its part biased downward by appropriate means. In the illustrated embodiment, disc spring102extends from within the valve body34over the upper piston94, and applies a downward force thereon when no opposite force is in play. The normally open plungers82nomounted on the upper piston94are therefore biased towards the open position.

An actuating mechanism is provided for actuating the plungers82of both types between their open and closed positions thereof. This can be accomplished in the current embodiment by controlling the distance between the upper and lower pistons94and90. When not actuated, the two pistons are in contact, as they are pushed towards each other by the Belleville assembly95and disc spring102. Referring toFIG. 5, the actuating mechanism preferably includes a pneumatic actuator formed by the two pistons90,94, the push plate92and the Belville washer96, and further includes a solenoid valve (not shown) or other appropriate system for supplying pressurised gas between the upper and lower pistons94and90through a cylinder port100. The gas will counterbalance the bias of both pistons by pushing the upper piston94upward, thus sliding the normally open pistons82notowards the closed position, and by pushing the lower piston90downwards, thus pulling the push plate92downward and retracting the normally closed pistons82nctowards the open position. Removing the pressurized gas will have the opposite result, due to the biasing effect of the Belleville assembly95and disc spring102.

Referring toFIGS. 5A and 5B, according to one embodiment of the invention, shims106are used within the valve body to limit the stroke of the lower and upper pistons90,94. Using shims of the proper thickness allows the use of a higher actuating pressure without requiring the use a pressure regulator to drive the valve, as in valves of the prior art.

Referring toFIGS. 2,4,5, and6, according to one embodiment of the invention the valve cap32and valve body34are held together by an appropriate number of holding screw70. In the illustrated embodiment, four (4) holding screws are provided, one in the center of the valve and the other forming a triangle there around. Of course, the holding screws could be provided in a different number and at different location, or other types of fasteners could be used so that the valve cap and valve body are held tightly together.

The valve30may optionally be provided with a purge circulation line56for preventing inboard and outboard leaks. Referring toFIG. 3, the purge circulation line56may include an outer annular channel58extending outwardly of the grooves40in the first interface36, and an inner annular channel60also extending in the first interface36but inwardly of the grooves40. Referring toFIGS. 6,6B,6C and6D, the purging line preferably includes a pair of fluid inlet62and fluid outlets63. Each pair has a first opening64in the inner annular channel60and a second opening66in the outer annular channel58, for providing a continuous fluid flow in each channel. Purging fluid is provided to the fluid inlets62through inlet cylinder port57and extracted through outlet cylinder port59. The outlet cylinder port59of the purge circulation line may also be connected to monitoring means112, so that a fluid leak captured by the purge line be detected.

As mentioned above, in accordance with a preferred embodiment of the invention there are provided communication mechanisms each operatively connecting a neighbouring pair of the grooves in the valve cap. On such mechanism is provided between each pair of ports between which fluid communication need to be alternatively allowed and interrupted. Such a communication mechanism will now be described with reference toFIGS. 3,7,8and9.

The communication mechanism first includes a communication port54opening in the first interface36at an intermediate position between the grooves to be operatively connected. The communication port is itself connected to a communication conduit52which extends within the valve cap32. The communication conduit52a port50opposite the communication port54opening in a first one40aof the grooves of a pair. Each of the communication conduits52of this preferred embodiment is drilled into the valve cap32, and has a shape of an inverted V with a circular cross section, the diameter of the communication port54being slightly larger than the diameter of the communication conduit52. Of course, the internal communication conduit may have other appropriate shape.

As mentioned above, the valve body is provided with recesses78within the second interface38and connected to corresponding passages76. The communication mechanism includes one such recess78, which is aligned with both the corresponding communication port54and with the second one40bof the grooves of the pair.

The diaphragm84is provided with a plurality of flexible sealing surface108each integral thereto and each part of a corresponding communication mechanism. For a given communication mechanism, therefore, the flexible sealing surface108is resiliently biased away from the first interface36, and is seated within the recess78when the plunger82mounted within the corresponding passage76is in the open position. This position is shown inFIG. 7. When the plunger is in the closed position, as seen inFIG. 8, it pushes up on the sealing surface108of the diaphragm84, which sealingly closes the communication port54.

In another preferred embodiment, the flexible sealing surfaces108may also be attached to the plungers, so that when the valve30is used in sub-atmospheric pressure applications, the sealing surfaces108are pulled towards the bottom of the recesses78when their corresponding plungers are retracted towards the open position.

In use, when the plunger82is in the opened position (as shown inFIG. 7), fluid communication is allowed between neighbouring process ports46aand46b. Fluid exits the process port46awithin the corresponding groove40a, which is surrounded by the diaphragm84. Fluid can therefore only exit through port50of the communication conduit52, which carries it the communication port54. As the flexible sealing surface is biased towards the bottom of the recess78, fluid is allowed within this recess78which allows it to flow to the neighbouring groove40b, where is exits the valve through the corresponding process port46b. When the plunger82is in the closed position (as shown inFIG. 8), the flexible sealing surface108of the diaphragm is pushed towards the communication port54, which is therefore completely blocked thereby preventing fluid from exiting the communication conduit52. Communication between the two process ports46aand46bis therefore prevented. Preferably the diameter of the communication port54is smaller than the diameter of the plunger82, effectively ensuring gas or liquid tightness.

As will be readily understood by one skilled in the art, the communication mechanism as explained above allows a positive shut-off on a communication port, the shut-off interrupting a flow between two adjacent process ports. Traditional gas chromatography diaphragm valves of the prior art interrupt the flow between two adjacent process ports by forcing a diaphragm on a surface between two process ports, rather than on an intermediate port.

In a preferred embodiment of the invention, as shown in the schematic representation ofFIGS. 10A and 10B, a diaphragm-sealed valve30allows for a traditional flow path found in chromatographic instruments. With this valve type, there is usually a continuous flow of fluid or liquid through all ports at all times, unless the valve is actuated. When the valve is actuated, all ports are closed to avoid an undesired mix of fluid or liquid within the valve.FIG. 10Ashows the valve in an “on” configuration, where the sample is injected into the carrier circuit, andFIG. 10Bshows the valve in an “off” configuration, where the sample loop is filled and swept with the sample gas. While the preferred embodiment concerns a valve used for a sample loop injection configuration, other configurations such as hearcut, back flush, column selection can be realized.

Although preferred embodiments of the present invention have been described in detail herein and illustrated in the accompanying drawings, it is to be understood that the invention is not limited to these precise embodiments and that various changes and modifications may be effected therein without departing from the scope or spirit of the present invention.