FLUID HANDLING SYSTEM

Cross Reference to Related Application:

This application is a continuation-in-part of U.S. Patent Application Serial No. 07/337,330, filed April 13, 1989 and entitled "Fluid Mass Flow Control System".

Technical Field;

The present invention relates to sealing means for a fluid handling system and its constituent parts to achieve and maintain leakproof operation. It is applic¬ able to various systems, including systems employing pressure transducers, or mass flow systems employing either mass flow measuring means or mass flow control¬ lers.

Background Art

The leakproof operation of fluid handling systems is in many cases critically important, such as in sys¬ tems employing pressure transducers, or in mass flow sys- tems of the type employed to measure the mass flow rate of fluids or fluidic mixtures, or to regulate or control mass flow rate, or to do both. For example, in process¬ es for manufacturing semiconductor substrates or inte¬ grated circuits a number of process stages or steps are involved which each require exact quantities of differ¬ ent kinds of fluid including gases. The flow controller

valve of the associated fluid mass flow control systems must meter fluid flows precisely and in a positive, leak¬ proof manner throughout many repetitions of operation and throughout a range of operating pressures. In certain integrated circuit and other analyti¬ cal industrial manufacturing processes gas flow takes place at relatively high pressures. Elastomeric O-ring seals are generally susceptible to leakage above approxi¬ mately 1,500 pounds per square inch. Beyond that point, and up to approximately 10,000 pounds per square inch, tubular or hollow 0-rings made of stainless steel or the like provide satisfactory sealing. However, unflawed 0- rings of this type are prohibitively expensive, are not readily available, and are not adapted for reuse once the interconnected parts are disconnected. Mass flow control systems in particular require a reliable low cost means to provide sealing against gas loss at higher pressures, and leakage at high vacuums.

Existing methods for the usual in-line or longitu- dinal assembly of modular components of a flow control system are also unsatisfactory. Typically, a modular component will include a threaded opening and an adja¬ cent elastomeric O-ring. A coupler having a central nut portion and opposite threaded ends is threaded at one end into the threaded opening of the modular component. The nut portion is then tightened to compress the O-ring and provide the desired seal. A similar arrangement is provided on the adjacent modular component. The external threaded ends of the two couplers are next secured to- gether by a length of conduit having a gland integral with each end of the conduit. A pair of internally threaded nuts carried between the opposite ends of the conduit are then threaded over the threaded ends of the

two couplers. Tightening of the nuts engages the glands and pulls the conduit against O-rings interposed between the ends of the couplers and the ends of the conduit. The leakproof connection of the two modular components thus requires two couplers, an intervening conduit, a pair of nuts to connect the conduit and the pair of coup¬ lers, and four O-rings. In addition to the undesirable multiplicity of fittings, the length of the assembly and the space it occupies are also o jectionable. A flow control system is normally situated in a "clean" room from which foreign particles are constantly being fil¬ tered, and making a clean room large enough to accommo¬ date lengthy assemblies is very expensive. U.S. Patent No. 3,521,910, issued to F. J. Calla- han et al July 28, 1970, and entitled "Tube Coupling", is another arrangement in the prior art for effecting a fluid tight coupling. The components to be connected together include integral bead or face seals in their end faces, a washer or gasket interposed between the face seals, and threaded couplers for engaging flanges on the components. Relative rotation of the couplers urges the components together and compresses the face seals and gasket to provide the desired sealing rela- tion. This type of arrangement was characterized by the presence of undesirable foreign particulate matter in the gases passing through the components, the face seals sometimes were not exactly aligned and thus could be undesirably urged laterally out of optimum sealing posi- tion upon tightening of the couplers, and the arrange¬ ment was also ill-suited for the coupling of large di¬ ameter or large nonσircular components because the coup¬ lers would have to be made even larger to receive and draw together such components.

The arrangement of filters in prior art flow con¬ trol systems is another problem. Contamination of pro¬ cess gases by particulate matter and the like is typical¬ ly prevented by the use of filters. These must be peri- odically cleaned or replaced. Since the filter assembly is usually one of the in-line modular components of the parent system, its removal requires unbolting of the as¬ sembly at its flanged connections. The filter is then longitudinally separated from the assembly for cleaning or replacement, and then the assembly must be carefully reassembled to maintain the leakproof operation. A better system is needed for servicing or replacing such filters, as well as analogous components, without having to disturb the parent assembly of other flow control sys- tem components.

It will be apparent from the foregoing that there is a need for a fluid mass flow control system that addresses each of the foregoing problems of prior art structures without loss of leakproof operation.

Disclosure of Invention

According to the present invention, a sealing means is provided which is adapted to operate with var¬ ious kinds of fluid handling systems including, by way of example and not by way of limitation, systems employ- ing pressure transducers, or mass flow systems employing components to precisely measure or control gas flow in a leakproof manner over a wide range of pressures, and par¬ ticularly at higher pressures and at ultra high vacuums. The present sealing means embodies a metal face or bead seal which enables operation of the associated system at pressures as high as 10,000 pounds per square

inch or at least as low as 1 x 10-11 torr. , with gas leakage as low as 2.4 x 10~ ¹⁴ cc/He/sec. The bead seals are employed in various parts of a mass flow con¬ trol system, for example, particularly between certain of the modular components to facilitate in-line or longi¬ tudinally oriented assembly of the components. Use of such bead seals enables all of the components to be con¬ nected together either by a single set of fastener means extending completely through the components and connec - ing to opposite end or mounting plates, or by multiple fasteners extending inwardly from each other. Use of such a sealing means thus eliminates the objectionable multiple fitting and seal type connections used in the prior art to achieve leakproof operation. It also eli - inates the rotational torque which abrades parts and causes particulate matter to contaminate the gases carried by the system.

In one embodiment the bead seal comprises a pair of annular projections or ribs made integral with or _Q carried by the end faces, respectively, of the adjacent modular components to be connected together. Each rib surrounds the gas flow opening in the end face and de¬ fines a rounded or radiused sealing surface. The bead seal further includes an annular sealing washer or gas- 5 ket made of metal disposed between the end faces of the abutting modular components. When the annular ribs of the respective components are brought together, the ribs press against the opposite faces of the interposed gas¬ ket to provide the desired high pressure or high vacuum 0 seal.

In another embodiment the bead seal comprises an annular member having opposite faces in which the annu¬ lar projections or ribs are integrally formed, respec¬ tively. The associated end faces of the modular compo- nents to be connected together each include an annular planar or flat face. When these faces are brought togeth¬ er against the intervening bead seal, the ribs of the bead seal press against the end faces of the modular com¬ ponents in fluid tight, leakproof relation. A modifica- tion of this embodiment includes a flat keeper or plate in which one or more of the annular beads or ribs are formed. The plate includes apertures or openings which cooperate with the fasteners connecting the modular com¬ ponents. This arrangement insures precise repeatability of rib location on disconnection and reconnection of the module components.

A preferred method and apparatus for urging the modular components together in a leakproof assembly com¬ prises the use of a pair of end mounts or plates located adjacent the end ones of the modular components to be assembled. Elongated, longitudinally continuous headed bolts are disposed through the end plates and through the components. The bolt heads bear against the outer portion of one end plate, and the opposite bolt ends are fixed in place by threaded fasteners or nuts tightened onto them and bearing against the associated end plate. This arrangement brings the sealing surfaces of all of the ribs into sealing engagement with the associated gaskets. The resulting assembly is leakproof and yet much shorter and less bulky than the analogous assem¬ blies of the prior art.

Use of the present sealing means in a fluid mass flow system enables use of a filter assembly which has a

base assembled to the adjacent modular components in the same in-line arrangement as the other components. The gas flow passages through the base of the filter assem¬ bly are laterally offset to communicate with a trans- versely oriented filter cavity defined by a filter cap and a portion of the filter base. This disposes the filter at right angles to the longitudinal axis of the filter base. Removal of the filter cap does not affect the leakproof characteristics of the assembly, and yet it provides access to the filter so that its replacement involves only lateral slidable separation from the fil¬ ter cavity, without any need for demounting of the com¬ plete filter assembly from the other modular system com¬ ponents. Other aspects and advantages of the present inven¬ tion will become apparent from the following more detail¬ ed description taken in conjunction with the accompany¬ ing drawings.

Brief Description of the Drawings

FIG. 1 is a longitudinal cross sectional view of the present sealing means used in a flow controller as¬ sociated with a fluid mass flow control system which also includes a control valve;

FIG. 2 is an enlarged detail view of the valve assembly of FIG. 1;

FIG. 3 is a longitudinal cross sectional view, partially in side elevation, illustrating the flow con¬ troller of FIG. 1 in combination with a filter and shut- off valve assembly; FIG. 4 is a partial perspective view of one of the end plates and an associated modular component, illustrating the details of the bead seal;

FIG. 5 is a side elevational view of a plurality of modular components connected in in-line relationship by a single or multiple set of elongated fasteners.

FIG. 6 is a transverse cross sectional view through the center of an alternate form of face or bead seal;

FIG. 7 is a top plan view of the seal of FIG. 7; FIG. 8 is a view similar to FIG. 2, but illustrat¬ ing only a portion of the structure, and showing use of the bead seal of FIGS. 6 and 7 and the manner in which components of the structure are formed to cooperate with the bead seal.

FIG. 9 is a plan view of yet another form of bead seal; and FIG. 10 is a transverse cross section of the seal of FIG. 9;

FIG. 11 is a plan view of yet another form of bead seal; and

FIG. 12 is a view taken along line 12-12 of FIG. 11.

Best Mode for Carrying Out the Invention

The present sealing means is applicable to any fluid handling system which must be characterized by virtually lealφroof operation under conditions of high pressures or high vacuum, and by an absence of abraded or particulate matter which could contaminate the fluids being handled. It has particular application to systems employing precision pressure transducers, and to fluid mass flow systems of either or both the mass flow meter or mass flow controller type. For illustrative purposes the system shown in the drawings is a mass flow control

system employing a mass flow controller to control the flow of gases which must be scrupulously free of contam¬ inants because of their use in producing semiconductor devices or the like. As seen in the drawings, and particularly in FIGS. 1 and .2, the mass flow system comprises a mass flow controller 10 having gas passage defining means in the form of an elongated gas block 12 having an axially or longitudinally oriented gas passage 14 characterized by an upstream or inlet port 16 and a downstream or out¬ let port 18. The terms "inlet" and "outlet" are merely exemplary and not intended to be limiting.

End mounts or end plates 20 and 22 are connected to the opposite ends of the gas block 12, respectively, and include threaded fittings to which are attachable suitable conduits (not shown) to feed gas to the up¬ stream end of the block 12, and to carry gas away from the downstream end to the process site (not shown) , as will be apparent to those skilled in the art. ^τhe connection of the end plates 20 and 22 to the gas block 12 is made fluid tight by the present sealing means, which takes the form of metallic face or bead seals, various embodiments of which will subsequently be described. The main conduit 14 includes branches or passage¬ ways 24 and 26 which in this embodiment are laterally oriented. However, the present invention also compre¬ hends so-called in-line mass flow control systems in which the gas passages are longitudinally or axially arranged.

The passageways 24 and 26 define, respectively, an inlet conduit to a valve assembly 25 of the flow con¬ troller 10, and an outlet passage from the valve asse -

bly to the outlet port 18. The valve assembly is opera¬ tive to control the quantity of gas flowing in either direction through the main conduit 14. Its connection to the gas block 12 is also made fluid tight by utiliz- 5 ing the same type of face seals used in assembling the in-line modular components.

Operation of the valve assembly 25 is controlled by any suitable form of control signal means 27. The control signal means 27 which is illustrated comprises a 0 sensor conduit defined by a pair of laterally directed passages 28 in the gas block 12, a pair of aligned, lat¬ erally directed passages 30 in a sensor base or mount 29 of the signal means 27, and a U-shape sensor tube 32 car¬ ried by the mount 29 and communicating with the passages

15 30. As will be seen, the control signal means 27 is con¬ nected to the gas block 12 in fluid tight relation by the same type of face seals previously referred to. Further, as previously indicated, the present invention can be used in association with an in-line sensor system

20 in which the sensor is aligned with the main gas flow, rather than being positioned laterally of the main gas flow.

The sensor tube 32 is the sensing passage through the control signal means. A heating coil 34 is disposed

₂₅ about the sensor tube 32 in order to heat gas flowing through the ube. Sensing coils 34 associated with the heating coil sense the upstream and downstream tempera¬ tures of. the heated gas.

As is well known, the gas that flows through the

3.0 sensor tube 32 absorbs heat produced by the heating coil 34, and the difference in temperatures at particular lo¬ cations along the sensor tube is indicative of the mass flow rate in the sensor tube, and consequently in the main conduit 14.

A suitable control means (not shown) converts the sensed rate of mass flow through the bypass conduit to a signal which operates the flow controller valve assembly 25 according to the rate of mass flow. The particular details of suitable sensing and control circuits are o- itted since they form no part of the present invention, and because they are well known to those skilled in the art.

The flow controller valve assembly includes a con- trol valve such as an electromagnet or solenoid, prefer¬ ably but not necessarily of the type described and illus¬ trated in U. S. Patent No. 4,569,504, issued February 11, 1986. This type of solenoid is responsive to sig¬ nals from the control system to move a valve element or pintle 38 of the valve assembly. To accomplish this a solenoid coil 36 is carried by a housing or frame 40 con¬ stituting the magnetic return path. The frame 40 sup¬ ports the solenoid coil in surrounding relation to a magnetic shaft or core 42. The core 42 is vertically elongated and is charac¬ terized by a threaded upper extremity which extends through an upper wall of the valve assembly frame 40. A fastening nut 44 secures the core 42 in position rela¬ tive to the valve housing upper wall. The lower end of the core 42 is characterized by a larger diameter base 46 which rests within a complemental annular cavity form¬ ed in a pole retainer 48. A thin horizontal wall sec¬ tion of the retainer 48 separates the core base 46 from a pole piece cavity 50 which, as best seen in FIG. 2, re- ceives an upper pole piece or plunger 52. Plunger 52 is vertically movable within the pole piece cavity without any contact with the walls of the cavity.

A bent or centrally deformed disk spring 54 is disposed between the upper surface of the plunger 52 and the undersurface of the adjacent horizontal wall of the pole retainer 48. The disk spring 54 exerts a bias which urges the plunger 52 downwardly. An equally impor¬ tant function of the spring 54 is to bear at its center against the central portion of the plunger 52, with the margins of the spring bearing against the adjacent walls of the pole retainer 48. This centers or axially aligns the central portion of the plunger 52 with the center- line of the pintle 38 so that the plunger does not con¬ tact the adjacent walls of the pole retainer 48.

The plunger 52 is characterized by a plurality of depending portions which extend into complemental, up- wardly opening recesses in a bottom pole piece 56. The centering action of the spring 54 upon the plunger 52 not only spaces the plunger 52 out of contact with the adjacent walls of the pole retainer 48, but it also spaces the depending portions of the plunger 52 from the adjacent walls of the complemental recesses in the bot¬ tom pole piece 56.

The pintle 38 is characterized by a threaded, up¬ wardly extending shank which is threaded, press-fitted or otherwise suitably secured within a recess provided in a vertically oriented shaft 58. The shaft 58 in¬ cludes an integral portion 60 which is threaded or force fitted within a central opening in the central portion of the plunger 52. This causes the pintle 38, shaft 58, and plunger 52 to move in unison. The bottom pole piece 56 includes a downwardly opening recess 62 having side walls which receive a valve seat holder or keeper 64. The recess 62 is in fluid communication with the outlet conduit 26 by means

of one or more of a plurality of gas passages 66 provid¬ ed in the valve seat keeper 64.

Fluid communication between the inlet conduit 24 and the recess 62 is provided by a central passage through a lock nut 68 and a valve seat passage 70 in a valve seat 72.

The upper portion of the valve seat passage 70 is normally closed by the lower end of the pintle 38, which is of a hemispherical, mushroom or tapered shape, as best seen in FIG. 2. The valve seat 72 is externally threaded for threaded receipt within a threaded, verti¬ cally oriented central opening in the valve seat keeper 64. If desired, the seat 72 could be made unthreaded and press-fitted into position, or be provided with a one-way keeper or wedging element (not shown) .

The valve seat keeper 64 upwardly engages the edge margin of a flat disk spring 74. The spring 74 is fixedly carried by the pintle 38 and bears against the underside of an annular portion of the bottom pole piece o 56. This annular portion is formed by the difference in diameters between the recess 62 and the opening within which the valve seat keeper is received. The combined action of the disk springs 54 and 74 urges the pintle 38 downwardly to a normally closed position. The lock nut 5 68 bears against the underside of the valve seat 72 and fixes it in position once the proper valve stroke has been established. A suitable sealing means in the form of an elastomeric plastic or metal O-ring 76 is disposed between the lock nut 68 and the adjacent portion of the 0 keeper 64 to prevent gas leakage between conduits 24 and 26.

The pole retainer 48 adjacent the cavity 50 in¬ cludes an annular, increased diameter portion having an

upper wall which is characterized by a circumferentially continuous protuberance or annular rib 78. The adjacent upper surface of the bottom pole piece 56 includes an i- dentical complemental rib 80 in confronting relation. An annular, relatively incompressible metal disk or wash¬ er 82 is located between these metal ribs 78 and 80. The combination of the ribs 78 and 80 and the washer 82 con¬ stitutes a sealing means in the form of a face or bead seal which seals, the cavity 50 from atmosphere. As will be seen, such bead seals are also provid¬ ed at various connection joints in the illustrated mass flow control system. They establish gas tight seals ef¬ fective at relatively high pressures or high vacuums. Their use in the valve assembly 25 enables the assembly to be tested for gas leakage independently of and prior to its assembly to the other components of the mass flow controller lOT. . If a valve must be replaced or removed and adjusted,; the valve assembly can then be tested for operation and for gas leakage characteristics before it is reconnected to the other components of the controller 10.

A bead seal like that described above is also pro¬ vided between the bottom pole piece 56 and the gas block 12 to seal *-off the recess 62 from atmosphere when the valve assembly 25 is connected to the controller 10. The bead seal includes a downwardly directed rib 84 inte¬ gral with the bottom pole piece 56, and an upwardly dir¬ ected rib 86 integral with an upwardly directed surface of a recess formed in the gas block 12, as best seen in FIG. 2. The seal also includes a gasket or washer 82 interposed between the ribs 84 and 86.

A plurality of headed fastening means or bolts 90 are disposed through suitable vertically oriented open-

ings provided in the pole retainer 38 and in the bottom pole piece 56. These openings are in communication with threaded openings (not shown) provided in the gas block 12 to receive the threaded ends of the bolts 90. Tight- ening the bolts 90 assembles the pole retainer 48 to the bottom pole piece 56, while also assembling the valve as¬ sembly 25 to the gas block 12, as will be apparent.

Tightening of the bolts 90 axially pulls together the components to establish a gas tight seal through the close engagement of the ribs 78 and 80 with the opposite faces of the washer 82, and through engagement of the ribs 84 and 86 with the opposite faces of the washer 88. No rotational torque is imparted to the ribs or the wash¬ ers. Consequently, there is no relative scrubbing or abrading which could generate undesirable particulate matter to contaminate the gases being handled.

As seen in the analogous arrangement of FIG. 4, which will be described, the ribs are precisely formed so as to be in exact, confronting and complemental rela- tion, the radius of each rib being made sufficiently small that high contact pressures can be developed with the washer. The contact is circumferentially continuous so that only slight deformation of the washer is neces¬ sary to provide the desired fluid tight seal. If desir- ed, each washer or gasket can be stamped or otherwise formed on its opposite sides to provide a circumferen¬ tially continuous or annular groove 97 in each side or face. The groove 97 is indicated in dotted outline in FIG. 4. The grooves are configured and dimensioned to receive the ribs in complemental relation, the diameter and depth of each groove being slightly smaller than that of the associated rib. Upon tightening of the bolts, the grooves then tend to compensate for slight

radial and circumferential dimensional tolerances of the ribs, and thereby insure precise alignment of the con¬ fronting ribs, and consequent optimum circumferentially continuous sealing. The metal of the washer should be softer or less hard than the metal of the ribs so that it is the washer which deforms under pressure rather than the ribs. This relative hardness can be achieved in any suitable man¬ ner, such as by selecting materials of the proper rela- tive hardness, or by selecting materials of the same hardness and annealing or otherwise treating the washer material to make it softer, as will be apparent to those skilled in the art.

The foregoing arrangement has operated very satis- factorily, providing a gas tight seal at pressures as high as 10,000 pounds per square inch, or as low as 1 x 10-11 torr. with gas leakage as low as 2.4 x 10~ ¹⁴ cc/He/sec. Use of zero clearance face or bead seals in a fluid flow mass flow control system is particularly advantageous to eliminate the multiplicity of prior art interior threads, flange connections and the like, and their accompanying particle generation and nucleation corrosion sites.

Although nickel is a preferred material for the washer of the bead seal for various reasons, including its resistance to corrosive gases, other materials can also be used, depending upon the pressures and gases in¬ volved, and the relative hardness of the bead seal and the surfaces which it engages. The preferred nickel washer is characterized by a close tolerance flat surface having the grooves 97 in order to contact the bead seal ribs in circumferentially continuous, coextensive engagement. All machining or

fabrication particles are removed from the washer prior to its assembly to eliminate particulate matter. An al¬ ternative technique is to polish a base sheet, apply a plastic coating to the base sheet to protect the washer surfaces, cut or otherwise separate a plurality of wash¬ ers from the base sheet, and thereafter strip away the coating from each individual washer just prior to use. This technique is useful in fabricating a sealing means in which the washer does not include the centering groove 97, and the flat washer surfaces provide the seal¬ ing contact with the ribs.

On connection of the valve assembly 25 to the con¬ troller 10, the operation of the valve element or pintle 38 is initiated by a control system (not shown) . The system processes signals received from the control sig¬ nal means 27 to operate the solenoid 36 accordingly.

As seen in FIGS. 1 and 3-5, the previously de¬ scribed face or bead seals also make it possible to con¬ nect the various modular components of a mass flow con- trol system in a leakproof or fluid tight relation with¬ out any need for the multiplicity of gland/nut connec¬ tions common in the prior art. Such modular components can include valves, filters, shut-off valves and like components whose function and construction are not perti- nent here. However, each is characterized by a central gas passage, end faces arranged in abutting relation, and fastener openings enabling their connection in longi¬ tudinally aligned, end-to-end relation. FIG. 3 illu¬ strates typical components 98, 100, 102 and 12. The abutting end face of each of the modular com¬ ponents includes an annular protuberance or rib, as pre¬ viously described in conjunction with the bead seals of the valve assembly 25. This is illustrated in detail at

94 in FIG. 5, which only shows operation of the rib in cooperation with a bead seal washer 96.

The illustrated components are assembled by a plurality of headed fasteners or bolts 104 which bring the complemental ribs 94 into forcible engagement with the associated washers 96. As seen in FIG. 6, the bolts 104 extend through suitable longitudinally extending openings in the modular components. In the illustrated arrangement the heads of the bolt heads are received within suitable recesses in the left end plate 20. The opposite, threaded ends of the bolts 104 are threaded into threaded openings in the right end plate 22. Exten¬ sion of the bolts completely through the components is one suitable arrangement. An alternative arrangement is the provision of threaded openings in the opposite ends of the gas block 12, and use of shorter bolts 104 thread¬ ed into such openings. Another option is the use of a combination of long and short bolts 104, and in which the elongated openings for the respective bolts are off- set to provide adequate clearance. The latter arrange¬ ment simplifies disassembly of the component 100, for ex¬ ample, since only the bolts 104 on the opposite end of the gas block 12 have to be removed. Each of these ar¬ rangements axially draws the components together without development of rotational torque. Such torques are unde¬ sirable becaμse they cause relative abrading movement between the dular component surfaces and the sealing means. As previously indicated, such abrading movement generates particulate matter which could contaminate the gases being handled in the system. The desired axial drawing together could also be accomplished, for exam¬ ple, by providing the adjacent portions of the compo¬ nents to be csnnected together with flanges or the like

(not shown) . Threaded fastening means coupled to the flanges, or annularly extending wedging means arranged around the flanges (not shown) , could then be operated to axially and nonrotationally draw together the compo- nents.

Compared to the gland/nut type of connection com¬ mon in the prior art, the foregoing use of through-bolts or similar axially acting means,in conjunction with face or bead seals enables modular components to be coupled together in an in-line, longitudinally oriented manner which significantly reduces both the length and bulk of the assembled components, and also the number of seals required to provide for leakproof operation.

It will be apparent from the foregoing that any modular component of a fluid mass flow system can be as¬ sembled in leakproof fashion, so long as each includes the bead seals like those described above. Such an as¬ sembly can easily be taken apart for substitution or re¬ placement of any of the components. Only the bolts 104 have to be removed.

As best seen in FIG. 3, the mass flow control sys¬ tem illustrated also includes a filter assembly 106 hav¬ ing a base 108 connected in a standard in-line, longitu¬ dinally oriented manner using face or bead seals like those just described. A filter cap 114 is secured to the base 108 by a nut 116 threaded onto a threaded boss 118 of the base 108. A flange of the nut 116 bears a- gainst a complemental flange of the cap 114 to bring the components into sealing relation. An annular filter cav- ity 110 surround a filter 112.

The base of the filter cavity 110 includes a re¬ duced diameter portion 120 which receives a sealing means or O-ring 122. This seals off the lower end of

the filter cavity. A similar sealing means or O-ring 123 at the top of the filter seals off the upper end of the filter cavity.

The base 108 includes an inlet gas passage 124 which opens into the filter cavity 110. It also in¬ cludes an outlet passage 126 in communication with the hollow center of the filter. Gas flowing from the inlet passage 124 thus passes into the filter cavity 110, through the wall of the filter, and downwardly into a bore 128 which communicates with the outlet passage 126. The lateral orientation of the components defin¬ ing the filter cavity enables filter 112 to be quickly and easily replaced simply by unscrewing the nut 116 and removing the cap 114. The filter can then be laterally withdrawn and replaced. The filter module or assembly 106 does not have to be disconnected from the adjacent modular components, and their leakproof relationship thus remains undisturbed. If desired, a flanged coup¬ ling (not shown) could be used in place of the nut 116, which would reduce generation of abraded particulate matter.

In the foregoing applications the face or bead seal has included a metal washer interposed between an¬ nular metal protuberances or ribs integral with the mat- ing surfaces. An alternate form of face or bead seal 130 is illustrated in FIGS. 6-8.

Use of the bead seal 130 has certain advantages compared to the type of bead seal already described. The first bead seal, shown in FIG. 2, comprises the e- tal washer 82 interposed between the annular projections or ribs 78 and 80. The ribs are cut, forged or other¬ wise formed out of the parent metal of the parts 48 and 56 to be secured together. In such an arrangement if a

rib is improperly formed or becomes damaged, the com¬ plete part must be discarded. This can be quite costly since the part is usually specially formed in other re¬ spects, as can readily be seen in FIG. 2. No ribs have to be formed in the parent parts in order to utilize the bead seal 130. Instead, the mating surfaces of the parts to be secured together are made planar or flat, and the seal 130 is disposed between them. If desired, the mating surfaces could be provided with annular grooves (not shown) to receive the ribs for exact centering.

The seal 130 is preferably made of corrosion re¬ sistant material such as 316 stainless steel and is made using the same careful fabrication techniques employed in fabricating the components of the previously describ¬ ed bead seal. The bead seal 130 comprises an annular or centrally apertured body 132 having opposite faces which are generally flat and parallel except for concentric an¬ nular protuberances or ribs 134 and 136 integrally form- © in the body 132. Each of the ribs 134 and 136 is lo¬ cated generally midway between the inner and outer cir¬ cumferential edges of the body 132.

In a typical installation the outer and inner cir¬ cumferences of the body 132 were made 0.260 inch and 0.140 inch, respectively. The outer and inner circumfer¬ ences defined by the juncture of each arcuately shaped rib where it merges with the associated planar face of the body 132 were made 0.230 inch and 0.170 inch. The depth of the section from the crest of one rib to the crest of the opposite rib was made 0.76 inch, and the height or thickness of each rib above its associated body face was made 0.18 inch. These dimensions are mere¬ ly exemplary and it will be apparent that they can be varied to suit a particular application.

The bead seal 130 is illustrated in FIG. 8 as it would appear when installed in the structure illustrated in FIG. 2. Parts shown in FIG. 8 corresponding to those of FIG. 2 are assigned the same numeral with the sub- script "b". It will be understood, of course, that the bead seal 130 is similarly substitutable wherever the previous bead seal was used. Additional drawings illus¬ trating this are therefore omitted for brevity.

FIG. 8 shows in dotted outline the appearance of the ribs of the bead seal 130 upon initial installation, while the full line showing of the ribs illustrates their deformation upon connection of the associated parts 48b and 56b. The degree of total compression or deformation of both ribs in the illustrated embodiment is approximately 0.008 inch. The amount of gas leakage in this arrangement has been found to be extremely low and well within the range acceptable in the most demand¬ ing mass flow control systems. It is in the order of 1 x 10-11 torr. with gas leakage as low as 2.4 x 10 ^"14 cc/He/sec.

The bead seal 130 is far superior to prior art metal O-ring type seals which are customarily fabricated out of small diameter, roll seamless tubing formed into a circle and welded at the abutting ends. Often the weld spoils the temper of the metal or the weld is crack¬ ed or porous, allowing atmosphere inside the ring to leak into the mass controller system and contaminate the gas mixture. Sometimes the weld fills a portion of the hollow interior of the O-ring and forms a plug at the weld point wh-Lch does not compress in the same manner as the remainder' of the hollow ring. To reuse such a ring is not possible because the plug area would have to be precisely located where it was located in the original

use in order to match the plug indentation formed in the surface contacted by the O-ring. Further, such O-rings sometimes tend to undesirably spread radially outwardly, a characteristic which is not shared by the bead seal 130, particularly where annular seating grooves (not shown) are provided in the component surfaces to accept the ribs.

FIGS. 9 and 10 illustrate a form of bead seal 138 made of solid rod or wire of circular cross-section, formed into a circle or O-ring configuration, and welded together at the free ends. Although not illustrated, the faying surfaces which are to be sealed can be made flat, and the seal 138 compressed between them. Alterna¬ tively, one or both of such surfaces can be provided with an annular seat to locate and receive the seal 138. The seal is preferably made of 316 stainless steel or similar corrosion resistant material that is compressible or deformable in the manner of the bead seal 130 illustrated in FIG. 9. Like the seal 130, the rounded or curvilinear configuration of the portion of the seal 138 which contacts the faying parts tends to flatten or deform slightly under pressure. It does not scar or cut into the faying surfaces, as would a V-shape for example. If the faying surfaces are cut or gouged, the bead seal could not be used again because of the virtual impossibility of exactly matching the position of the seal in successive uses.

FIGS. 11 and 12 illustrate yet another form of bead seal 140. It is comparable to the bead seal of FIGS. 6-8. It is made of similar materials and is made in such a way that it can be precisely relocated in its original position in the event that it has to be removed for separation of the mass flow system components with

which it is associated. It is adapted to provide a plur¬ ality of sealing means in a unitary part.

The bead seal 140 comprises a keeper or plate 142 having edge margins configured to mate with the edge mar- gins (not shown) of the component parts which are to be maintained in sealed relation by the bead seal 140. The plate 142 in the illustrated configuration also has a pair of gas ports 144 adapted to align with gas ports (not shown) in the component ports to be secured togeth- er. Each gas port 144 is surrounded by an annular rib or bead 146.

The bead seal 140 is fabricated to provide pol¬ ished, particulate free surfaces without sharp edges or burrs. The plate 142 is flat and is of lesser thickness than each bead 146. The thickness of the plate is sel¬ ected to limit the degree of deformation of the beads 146. This is advantageous to prevent permanent defor¬ mation of the beads when the associated fastening means is advertently operated to develop excessively high seal- ing pressures. In one application the plate 142 is 0.024 inch thick, each bead or rib is 0.25 inch in dia¬ meter, and the radius of each rib, and the radius of an annular groove 148 defining the outer portion of each rib, is.0.015 inch. Precise dimensions can be achieved in any suit¬ able manner, but it has been found that chemical etching produces good results. This etching process is well known in the art and involves selective applications of a photographic emulsion to the surfaces of a larger or parent sheet of material to define the areas to be etch¬ ed away. Many individual plates 142 and associated beads 146 are defined in the parent sheet, separated by weakened areas (not shown) for easy separation of indivi-

dual plates 142. The finished parent sheet is covered with protective plastic to prevent damage of the sheets during storage and handling. Individual plates 142 are then separated from the parent sheet as needed. The arrangement of FIGS. 11 and 12 eliminates the multiplicity of parts previously needed to seal a plural¬ ity of gas passages associated with the ports 144.

The component parts between which the bead seal 140 is disposed for sealing are characterized by four openings (not shown) to receive elongated fasteners like the fasteners 104 in FIG. 5. The plate 142 includes four openings 150 to receive such fasteners in close tol¬ erance relation. If desired, precision collars (not shown) can be used to achieve such close tolerances, with nonprecision fasteners being disposed through such collars to achieve the desired closure or sealing forces. This enables the beads 146 to assume the same relative position despite disconnection and reconnection of the component parts. Thus, any slight deformation of the flat surfaces of these parts by the beads 146 for each gas opening will be exactly matched on each recon¬ nection to preserve the gas tight integrity of the con¬ nection at such gas openings. As was the case with pre¬ vious embodiments, the fasteners develop axial, nonrota- tional sealing forces, thereby eliminating the develop¬ ment of abraded, contaminating particulate matter.

From the foregoing it will be apparent that the present sealing means is adapted to provide a very effec¬ tive fluid tight seal at elevated pressures or under high vacuums. The fastener means employed develops ax¬ ial, nonrotational sealing pressures. Also, as previ¬ ously indicated, the valve assembly is adapted to be subassembled and tested separately of the remainder of

the associated mass flow controller. Heretofore, the valve assembly was commonly tested as a part of the complete assembly. If there were any malfunction, the complete assembly had to be taken apart to replace or adjust the valve components.

The filter assembly enables easy filter replace¬ ment without any need for disassembly of the filter as¬ sembly from the adjacent modular components, and conse¬ quent disconnection of the fluid tight joints. Most importantly, the bead seals uniquely enable the various components of a mass flow control system or the like to be connected together quickly and easily in a compact, gas tight assembly.

Various modifications and changes may be made with regard io the foregoing detailed description with¬ out departing from the spirit of the invention.