US3386472A

US3386472A - Valves for gas chromatography

Info

Publication number: US3386472A
Authority: US
Inventors: Eugene L Szonntagh
Original assignee: Leeds and Northrup Co
Current assignee: Leeds and Northrup Co
Priority date: 1965-03-25
Filing date: 1965-03-25
Publication date: 1968-06-04
Anticipated expiration: 1985-06-04

Description

June 4, 1968 E. L. SZONNTAGH VALVES FOR GAS CHROMATOGRAPHY 5 Sheets-Sheet 1 Filed March 25, 1965 June 4, 1968 E L. SZONNTAGH ,4

VALVES FOR GAS CHROMATOGRAPHY Filed March 25, 1965 5 Sheets-Sheet 2 Fi s it! E w June 1968 E; SZONNTAGH 3,386,472

VALVESFOR GAS cnaom'roemrnv Filed March 25, 1965 5 Sheets-Sheet 5 June 4, 1968 E. L. SZONNTAGH VALVES FOR GAS CHROMATOGRAPHY 5 Sheets-Sheet 4 Filed March 25, 1965 WA l IBA lll

MHH

June 4, 1968 E. SZONNTAGH 3,386,472

VALVES FOR GAS CHROMATOGRAPHY Filed March 25, B65 5 Sheets-Sheet 5 l4 5 57 "7A "10 4C 56 "7B 35 m 5? 77; 24A a; 24s

n 3 A I United States Patent 3,386,472 VALVES FOR GAS CHROMATOGRAPHY Eugene L. Szonntagh, Flourtown, Pa., assignor to Leeds & Northrup Company, Philadelphia, Pa., a corporation of Pennsylvania Filed Mar. 25, 1965, Ser. No. 442,662 12 Claims. (Cl. 137-597) ABSTRACT OF THE DISCLOSURE Various gas-sampling valves for chromatographic systems: all sampling valves disclosed are of modular construction with a sampling cavity formed between opposed faces of valve body blocks which have internal flow passages extending to the cavity. The movable valve element, a flapper or reed, is mounted within the sampling cavity and is directly actuated by magnetic means including stationary pole-pieces extending to the sampling cavity and there adjacent the path of movement of the valve member.

This invention relates to gas-sampling valves suited for use in gas chromatographic systems.

The main objectives of the present invention are to provide a gas-sampling valve which is small and compact, which can be economically manufactured, which can be used for both conventional-speed and high-speed gas chromatographs, which has very small dead volume, which has no moving parts such as shafts or linkages which develop friction, which has low operating-energy requirements, which preferably does not require air or other auxiliary gases for its operation, which has a lifetime of the order of millions of sampling cycles, and which is very fast-acting to obtain sharp peaks in the chromatograms. Gas-sampling valves heretofore used have failed to meet many of such objectives.

In accordance with the present invention, the valve body is of modular construction and specifically may comprise a pair of blocks having engaging faces, at least one of which is recessed to define the sampling chamber or cavity. The movable valve element, preferably a flapper or reed, is mounted within the sampling chamber and controls flow of gas to or from the sampling cavity via passages within the blocks having ports communicating with the cavity in the path of the flapper or reed. The movable element of the valve is directly actuated as by magnet means having a pole-tip structure extending to the cavity at or adjacent the limits of movement of the reed, flapper, or other movable valve element. The cavity is shaped and dimensioned to provide minimal clearance for the movable valve element.

The invention further resides in a valve having new and useful features of construction, combination and arrangement hereinafter described and claimed.

For a more detailed understanding of the invention, reference is made to the following description of preferred embodiments thereof and to the accompanying drawings in which:

FIG. 1 is an explanatory figure in part including a sectional view of a dual valve embodying the invention;

FIG. 2 is a partial sectional view taken in end elevation on line 22 of FIG. 1;

FIG. 3 is an exploded view showing in perspective the various components of a dual valve similar to that of FIGS. 1 and 2;

FIG. 4 shows in perspective a valve assembled from the components of FIG. 3;

FIG. 5 is a side elevational view, partly in section, of a dual valve unit generally similar to that of FIG. 4;

3,386,472 Patented June 4, 1968 FIG. 6 is an end view taken in section on line 6-6 of FIG. 5 with the magnet structure omitted;

FIG. 7 is a bottom plan view of the upper valve-body block shown in FIG. 5;

FIG. 8 is a top plan view of the lower valve-body block shown in FIG. 5;

FIG. 9 schematically illustrates a dual-column chromatographic system incorporating a valve such as shown in preceding figures;

FIG. 10 schematically illustrates another dual-column system with back-flush provisions and incorporating two valve units such as shown in preceding figures;

FIG. 11 is a sectional view showing a basic valve subassembly of a modification of FIGS. 5 to 8;

FIG. 12 shows the sub-assembly of FIG. 11 as completed for actuation by a stationary electromagnet;

FIG. 13 shows the sub-assembly of FIG. 11 as com pleted for actuation by a movable permanent magnet;

FIG. 14 is a sectional view of another modification of the sampling valve;

FIG. 15 schematically shows the valve of FIG. 14 and a suitable excitation circuit;

FIG. 16 is a perspective view, partly in section, of another modification with mechanical biasing means releasably to hold the movable valve member in both control positions; and

FIG. 17 is a side elevational view, in section, of the sampling valve of FIG. 16.

As schematically shown in FIG. 1, the valve unit 10 essentially consists of four main components; namely, the

body blocks

11 and 12, the reed or flapper 13 and the electromagnet 14. The reed 13 is the only movable element of the valve unit and is directly actuated by the electromagnet 14 without intervention of any mechanical linkage or coupling. The valve chamber 15 may be formed by recessing the face of at least one of the

blocks

11, 12 and may be of small volume, not greatly in excess of that required for clearance of the movable flapper element 13.

For the dual-valve unit shown, the flapper 13 is fastened intermediate its

free ends

13A, 13B as by bolt 16 to one or the other of

blocks

11, 12. The tips of the

pole pieces

17A, 17B of the electromagnet 14 extend through the upper block 11 to the top face of chamber 15 more or less adjacent the opposite

free ends

13A, 13B respectively of reed 13. The

pole pieces

17A, 17B are sealed into the block, and being stationary pose no leakage problem between chamber 15 and atmosphere.

The reed 13 is preferably of springy metal so shaped or formed that it is biased away from the pole-piece structure by its own resiliency and is of steel or like magnetic material to itself serve as an armature for the electromagnet 14. At least for some applications, the reed 13 is coated with Teflon or other corrosion-resistant material. The free ends of the reed 13 are respectively provided with

sealing tips

18A, 18B of yieldable material such as silicone rubber which may or may not have a coating of protective material. Other suitable materials may be used instead of silicone rubber.

With the electromagnet 14 in deenergized state, the tip 18A is firmly pressed by the spring action of reed 13 against the valve seat 19A formed by the end of a smallbore tube 20A. This small metal tube has a snug push fit into the block to form passage 21A of the lower body block 12. For the dual valve construction shown, the tip 18B of valve member 13 is similarly pressed against the valve seat 19B formed by the end of the small tube 203 which is tightly fitted into the block 12 to form a passage 21B of the lower body block 12.

When electromagnet 14 is energized, as by closure of the timing or programming switch 22 in circuit with a battery or other current source, each of the free ends 13A,

13B of the reed 13 is attracted toward the

corresponding pole tip

17A, 17B, flexing at or near the mounting screw 16 or equivalent. Accordingly, the sealing tips 18A, 1813 move away from the valve seats 13 A, 1913 respectively and into engagement with the

valve seats

23A, 23B formed by the ends of

small metal tubes

24A, 24B tightly fitted into the lock 11 to form the

flow passages

25A, 25B of the upper valve-body block 11. An enlarged portion of the left end of the reed 13 and the associated parts are shown in FIG. 2.

As one example of use of valve 19 in gas chromatography, the passages 25A, 253 are connected (FIG. 1) by suitable tubing or piping to serve as the inlet and outlet lines for a carrier gas and the

passages

21A, 21B are connected to serve as the inlet and outlet lines for a gas to be analyzed. Upon encr ization of electromagnet 14- of a brief period, the valve chamber is filled with a predetermined volumetric sample of gas to be analyzed. Upon de energization of the electromagnet after such period, the flow of carrier gas through the valve chamber 15 is resumcd to carry along with it the introduced sample. Because of the fast action of the reed valve 13 and the small volume of chamber 15, the time of introduction of all of the sample into the carrier stream is clearly defined with the precision required for accurate analysis by chromatographic methods; specifically, the fast positive action of the valve insures sharp peaks in the record or chomatogram as made by the usual detector and recorder arrangement.

Preferably and as shown, the carrier-gas passages A, 25B are interconnected within the upper valve-body member 11 by the capillary by-pass passage 26, and the sampled

gas passages

21A, 21B are similarly interconnected within the lower valve-body member 12 by the capillary passage 27. There is thus avoided the need for external piping and fittings to effect by-passing of the valve for either or both gases.

A more detailed illustration of all components of valve 10 appears in FIG. 3; the elements previously referred to are identified by the same reference characters. A gasket 28 of silicone rubber or other suitable material is clamped between the valve-

body blocks

11, 12 as by

bolts

29, 30 which hold the blocks together in the assembled valve (FIG. 4). The body blocks 11, 12 may be molded from a suitable fluorocarbon such as the trade name product Kel-F marketed by Allied Chemical Corporation or other plastic which is dimensionally stable and inert at least to most gases analyzed by chromatographic techniques. Alternatively, the body blocks may be of metal, such as stainless steel, which is itself corrosion-resistant, or may be of other non-magnetic metal sprayed or otherwise coated with a fluorocarbon material such as that sold under the trade name Teflon by E. I. du Pont de Nemours & Company, Incorporated, to present non-corrosive surfaces to the gases supplied to the sampling cavity. The

tube connections

33A, 33B of the upper block 11 respectively communicate with the

passages

25A, 25B of the upper valve-body block 11. The

pipe fittings

34A, 34B of the lower block 12 respectively communicate with the passages 21A, 213. Before the blocks 11, .12 are assembled, the flapper or reed 13 is fastened in fluid-tight relation to the upper face of the lower block 12 by the bolt 16 in position for alignment with the elongated recess 32 of the upper block. The provision of clamping

bolts

29, 29 at the ends of the blocks and of the intermediate clamping bolts 36, 30- insures distribution of the clamping pressure about the peripheral area of gasket 28 to insure a good seal between the valve cavity 15 and the atmosphere. If the gasket 28 is thin, most of the volume of the valve chamber 15 is that of the recess 32 of the upper block 11. The gasket 28 may be of substantial thickness, in effect forming a third-body block, whose shaped cutout provides most, if not all, of the sampling cavity. The various passages in the valvebody blocks may be formed by drilling straight through the block as indicated, and

then filling the unused end portions with plugs which may be of Lucite or Hysol rod cemented in place or a prefabricated tube structure forming the desired passages may be molded in place when making up the valve body blocks.

A generally similar valve unit 10A is shown in FIGS. 5 to 8 on somewhat larger scale. These figures are sectioned to show the plugs 35 for blocking otf unused portions of various passages in the valve body and to show the wells or recesses 36, 37 surrounding the valve seats. These wells permit the reed 13 to have sufficient stroke for adequate clearance of the open ports and firm pressure against the closed ports without corresponding increase in the volume of chamber 15. The diameter of the

recesses

36, 37 slightly exceeds that of the

sealing tips

18A and 188.

It should be evident from the sectioned portions of FIGS. 5 and 6 that when the electromagnet 14 is in deenergized state, the reed 413 is practically hat against the lower wall of chamber 15 as defined by the upper face of block 12 with the sealing tip 13A accommodated by the recess 35 about the lower valve seat 19A. When the electromagnet 14 is in energized state, the reed 13 is practically flat against or closely spaced from the sloping up per wall of chamber 1'5, as defined by the recess 32 in block \11, with the sealing tip 18A of the reed accommodated by =the well 37 for firm engagement with the upper valve seat 23A. The electrical energy requirements of electromagnet 14 for fast positive action and firm seating of the flapper valve 13 are small, i.e., less than five watts in the specific example later given.

As best shown in FIGS. 5 and 6, the tips of the

pole pieces

17A, 17B each receive a washer and an O-ring of silicone rubber or the like for positioning and sealing purposes. Before the body blocks 11, 12 are clamped together, the electrom-agnet unit 14 is assembled with the upper block 11 bypassing the

pole tips

17A, 17B into and through the holes 41, 41 extending upwardly from the recess 32 in the lower face of the block to the well 42 in the upper face of the block. With the pole tip faces practically flush with the upper face of recess 32, the magnet unit is temporarily held in position by the set screws 43 threadably received by block 11 and engaging opposite sides of both pole pieces. The well 42 is then filled with a suitable cement, as are also the lower ends of the holes 41, to preclude leakage from chamber 15 of the assembled valve.

As best shown in FIG. 6, the valve unit 10A has no projecting pipe fittings: instead, an annular groove or recess 38 is cut or formed about the end of the various inlet and outlet passages to receive O-rings 39 of silicone rubber or the like. Thus, when unit 10A is clamped against another ported unit of the system, the flow paths are connected without pipes or fittings. If a particular passage of unit 10a is not to be used, the corresponding recess 38 is used for a sealing cap instead of an O-ring.

The modular construction above described permits the valve unit to be of a small size. By way of specific example, the overall dimensions of a valve body made in accordance with FIGS. 5 to 8 may be approximately 2 /2" x A" x 1". The read 13 used thereinis carbon steel about 0.13" wide and 1.5" long and 0.031" thick. Its central area is milled to about 0.007" thick. It is hardened after machining to afford the desired spring action. From tests made on such a valve, it was determined that with a sample flow rate of 200 milliliters per minute, the variation of the cavity-charge when the charging time is of the order of one-half second results in less than 1% suppression in the recorded peak heights. At higher flow rates, the suppression in peak heights is much smaller. Likewise, for a charge time in the range of one second or more results in less than suppression of peak heights even at the above-mentioned low flow rate. For a valve unit of this size, the useful sample cavity size is between about 0.1 ml. to 1.0 ml; smaller sample sizes may readily be realized by sealing down the dimensions of the unit.

In FIG. 9, there are shown

passages

40A and 40B included in a valve of the type shown in FIGS. 1-4. For the type of sample injection above described in connection with FIGS. 1-4, the

passages

40A, 40B extending directly to opposite ends of chamber 15 are either omitted or blocked off. These passages are present or unblocked when valves of the construction shown in FIGS. 5 to 8 are used in systems such as those of FIGS. 9 and 10 hereinafter described.

For dual column operation without back-flush (FIG. 9), only one-half of valve 10A need be used for gasswitching purposes. To that end, the valve chamber is effectively divided into two smaller chambers by the sealing plug 44 which fills its central portion. For this application, the by-

passes

26, 27 are blocked by plugs 35. With the electromagnet 14 deenergized, the flapper valve 13A is in its lower position blocking the passage 21A: consequently, the gas to be analyzed flows through the No. 1 column 45,

passages

40A, 25A of the valve body and the dummy column or adjustable restriction 46 to the detector 47 associated with recorder 48. With the electromagnet 14 in energized state, the flapper valve 13A is in the upper position shown to block the passage 25A: consequently, the gas to be analyzed flows through No. 1 column 45,

passages

40A, 21A of the valve body, and through No. 2 column 49 to the detector 47. A suitable detector and recorder arrangement for chromatographic analysis is described in application Ser. No. 150,783, now Patent No. 3,205,701, filed Nov. 7, 1961, by Jeno L. Szountagh.

Alternatively, the arrangement shown in FIG. 9 may be used for dual column operation using both halves of the valve 10A. Such alternative arrangement is the same as that of FIG. 9 except that the output line from the dummy column 46 is connected to passage 25B and the output line from No. 2 column 49 is connected to passage 21B. The input to detector 47 is then from passage 4013. This avoids intermixing of the outputs from No. 2 column 49 and the dummy column 46 as supplied to the detector 47. In such an alternative arrangement, the

bypasses

26 or 27 are either omitted or plugged adjacent the

passages

21B and 25B.

For dual column operation with back-flush (FIG. 10), two valve units such as shown in FIGS. 5-8 are used for gas-switching purposes. The chamber 15 of each unit is effectively divided into two smaller chambers by a plug 44, as in FIG. 9, and three of the resulting reed-controlled chambers are included in the controlled flow paths. With the electromagnet of each unit in energized state, the

reeds

13A, 13B and A13 of units 10A and A10 are in the position shown: consequently, the mixture of carrier and sample gases to be analyzed flows to the No. 1 column 45 via

passages

21A, 40A of unit 10A, from column 45 to the No. '2 column 49 via the

passages

21B, 40B of the same unit and from the No. 2 column 49 to the detector 47. (Solid line arrows indicate the direction of flow with the magnets energized.) With the electromagnets of both units in deenergized state, the

reeds

13A and 13B of unit 10A close the

passages

21A, 21B and

open passages

25A, 25B of that uni-t, and the reed A13 of unit A10 closes passage A21 and opens passage A25 of that unit: consequently, the gas now flows in the reverse direction through the No. 1 column via the passages A40, A25 of valve unit A10 and from the No. 1 column 45 to atmosphere via the

passages

40A, 25A of valve unit 10A: some of the gas also flows to the No. 2 column 49 via dummy column 46 and

passages

25B, 40B of valve unit 10A. (The dotted-line arrows indicate the direction of flow with the electromagnet deenergized.) As in FIG. 1, the energization and deenergization of the electromagnets of the valve units are controlled by a suitable program switching arrangement of the associated chromatographic system.

For an arrangement known by those skilled in the art as Dual-column Back-flush Measure, the system of FIG. 10 would be utilized by adding thereto suitable connections to the other half of valve unit A10 not shown. The connections would comprise an additional dummy column or an adjustable orifice with its input side connected to 25A of valve 10A and its output side connected to B25 of valve unit A10 (not shown). The discharge end of No. 2 column 49 would be connected to B21 of unit A10 and B40 connected to the detector 47.

As will be understood by those skilled in the art, there are a great many different column and detector switching arrangements which can be constructed utilizing applicants valve structures.

There are many other ways of constructing valves in accordance with applicants invention, some of which are illustrated in FIGS. 11 to 17.

The principal difference between the sub-assembly construction shown in FIG. 11 and those previously described is that the pole tips 117A and 117B (not shown) are individual elements which are made an integral part i the upper body block 111 as by casting the plastic block about them or as by screwing or forcing them into a preformed body of plastic or non-magnetic metal.

As will be understood from FIG. 12, to make an electromagnetically-operated valve from the sub-assembly of

blocks

111, 112 of FIG. 11, the core 59 of coil 114 may be suitably fastened, as by bolts 50, to engage the exposed upper ends of the pole tips 117A, 117B (FIG. 12). The pole tips 117A, 117B may be of soft iron, in which event the

upper ports

24A, 24B of the valve are closed by valve element 3 only so long as coil 114 remains energized. Alternatively, the pole tips 117A, 117B may be hard iron or steel. In such case, momentary energization 1 of coil 114 causes movement of valve element 13 to close the upper ports and the residual magnetism of the pole tips sufiices to hold the valve member 13 in the attracted position. Release of the valve member 13 for return to engagement with the lower ports or valve seats 19A and 193 (not shown) occurs upon momentary energization of coil 114 in reverse sense. Preferably for this momentary-energization type of operation, the movable valve element 13 is permanently magnetized to afford a snap action.

The combination of the sub-assembly of FIG. 11 may also be used to make gas-sampling valves (FIG. 13) which are actuated in response to change in position of a permanent magnet 51 as effected by a timing cam, or pneumatic or fluid motor, or manually by an operator. Specifically, the permanent magnet 51 is mounted Within the recess 52 in the lower face of a third block 53 held as by bolts 12913 to the sub-assembly or combination of

blocks

111, 112. The magnet 51 is biased away from the pole pieces 117A, 11713 by spring 54 so that normally the valve member 13 is at its lower-limit position to close the

lower ports

19A, 19B. When the plunger 55 is depressed, the pole pieces 117A, 117B are magnetically excited to attract valve member 13 to its upper-limit position for closure of the

upper ports

24A, 24B.

In the modification shown in FIG. 14, the upper body block 111 has a third central pole piece 117C, a central recess 56 for receiving coil 14C, and a top slot or recess 57 for receiving the magnetic yoke member 58. With the coil 14C and yoke member 58 in place, this body block 111 may be combined with body block 112 to afford a more compact version of the electromagnetically o erated valves of FIGS. 4, 5 and 12. With the coil 14C and yoke member 58 omitted, the body block 111 may be combined with body block 112 and block 53 to provide, as in FIG. 13, for actuation of the valve member 13 by movement of a permanent magnet.

In the assembly shown in FIG. 14, the lower body block 112 is of the same construction as the upper body block 111, i.e., it has three pole tips A117, B117 and C117, a recess 56 for receiving coil C14 and a groove for receiving a yoke 58. First assuming the movable valve element is a centrally fastened reed, it should be clear from the preceding discussion that energization of coil 14C alone will eifect upward flexure of the oppposite ends of the reed to close the upper ports of the valve and that energization of coil C14 alone will effect downward flexure of opposite ends of the reed to close the lower ports. When, as shown in FIG. 14, the movable valve element 13C is pivoted at its center, rocking of the member 13C in one direction eitects closure of one pair of diagonally opposite upper and lower ports (19A, 24B) and rocking of member 13C in opposite direction effects closure of the other pair of diagonally opposite upper and lower ports (19B, 24A). With the lever type valve member 13C permanently magnetized, the coils 14C, C14 are so connected in series and wound that when they are energized in either sense, the pole tips 117A, 117B are of one like polarity (S8. or N.N.) and the pole tips A117, B117 are of the opposite like polarity (N.N. or 8.8.), the polarity of all pole tips reversing with reversal in the sense of energization of the coils. Thus, upon momentary energization of coils 14C, C14 in one sense, the valve member 13C is rocked to engage

ports

24A, 19B and is held in that position after deenergization of the coils by the attraction between pole pieces 117A, B117 and the corresponding magnetized ends of the valvearrnature member 13C. Upon momentary energization of coils 14C, C14 in reverse sense, the valve member 13C is rocked to engage

ports

19A, 24B and is held in that position after deenergization of the coils by the attraction between pole pieces A117, 117B and the corresponding magnetized ends of valve-armature member 13C. For both directions of movement, the valve-armature ISO is repelled by the pole tips previously engaged by it and attracted by the pole tips toward which it is moving.

A suitable circuit for effecting actuation of the valve member 13C from one to another of its flow-control positions is shown in FIG. 15. The valve windings 14C, C14 are connected through oppositely poled diodes in series across an AC current source, such as the secondary winding 60 of a transformer 61 supplied from a power line. The oppositely poled

diodes

62A, 62B are connected in the series circuit and are respectively associated with the normally-open shunting switches 63A, 6313. When switch 63B is momentarily closed, the current passed by rectifier 62A energizes the coils 14C, C14 to move the valve 130 to one of its flow-control positions. When switch 63A is momentarily closed, the current passed by rectifier 62B energizes the coils 14C, C14 in reverse sense to move valve 13C to its opposite flow-control position. With both switches open, no current is supplied to the valve coils because of the blocking action of the diodes. The

switches

63A, 63B may be ganged and biased to normallyopen position from which either one, but not both, can be moved to its closed-circuit position.

In the modification shown in FIGS. 16 and 17, the movable valve element 13D is releasably held in both of its flow-control positions by mechanical biasing means. Specifically, the movable valve element 13D is firmly held in each of its two flow-control positions by the spring 65. The opposite ends of the spring 65 are hooked into, or otherwise suitably held to, the opposite free ends or short sides of the movable valve element 13D. The two long sides of the movable valve element are centrally fastened, as by

screws

16, 16, to the spaced posts 66 so effectively to provide a pivot or flexure point which is above the ends of the spring 65 for the valve position shown in FIGS. 16, 17 and below the ends of spring 65 for the opposite valve position.

Thus, when coil 140 is energized to attract the free ends of valve mem 'er 13D, the spring 65 serves as an over-center toggle t snap the

valve tips

18A, 18B away from engagement with the port seats 19A, 19B and into engagement with the port seats 24A, 2413. Such engagement is maintained after deenergization of coil 14C by the tension of spring 65. Upon subsequent energization of coil C14, the free ends of valve member 13D swing in reverse direction beyond the line of centers to snap the

tips

18A, 18B away from

port seats

24A, 24B and into engagement with

port seats

19A, 19B. Such engagement is maintained after deenergization of coil C14 by the tension of spring 65.

It shall be understood the invention comprehends not only the specific valve arrangement disclosed and described but also modifications and equivalents thereof within the scope of the appended claims.

What is claimed is:

1. A valve unit comprising a valve body having a sealed flow-cavity therein,

a movable valve member supported intermediate its opposite free ends within said cavity, each of said free ends being associated with at least two flow passages extending through said valve body to said cavity,

means for actuating said valve member comprising at least one electromagnet having two pole-pieces extending through said valve body to said sealed cavity and there respectively adjacent the path of said two free ends of the valve member, each end of said valve member selectively opening or closing at least one of said associated flow passages under control of said electromagnet.

2. A valve unit as in claim 1 in which the last-named means is electromagnetic means energizable to effect movement of said valve member to and from either of two flow-control positions, and

in which said valve member is releasably held in each of said positions after deenergization of said electromagnetic means by magnetic attraction between the valve member and adjacent pole-piece structure.

3. A valve unit comprising a valve body having at least two non-magnetic blocks held face-to-face with a. recess in at least one of the faces providing a sampling cavity isolated from atmosphere,

at least two flow passages in said body blocks terminating in ports within said sampling cavity,

a valve member at least in part of magnetic material mounted for movement in said cavity to control flow through said ports,

stationary magnetic pole-piece structure immovably sealed into and extending through at least one of said blocks to said cavity into proximity with the path of the magnetic part of said valve member, and

means for changing the excitation state of said stationary pole-piece structure to effect movement of said valve member with respect to said ports,

said last-named means comprising electromagnetic means energizable to efiect movement of said valve member to and from either of two flow-control positions, and

additionally includes, within said sampling cavity, me-

chanical biasing means releasably to hold said valve member in each of said positions after deenergization of said electromagnetic means.

4. A valve unit comprising a valve body having a sealed cavity therein,

at least two flow passages extending through said valve body at each end of said cavity,

a reed-valve mounted intermediate its opposite free ends within said cavity with each of said free ends at a corresponding end of the cavity, and

actuating means for said reed-valve comprising at least one electromagnet having two pole pieces respectively adjacent the two free ends of the reed-valve,

each end of the reed-valve selectively opening or closing at least one associated flow passage in dependence upon the excitation state of the pole pieces.

5. A valve unit as in claim 4 in which a first pair of flow passages respectively controlled by the opposite ends of the reed-valve enters the same side of the cavity whereby flow of fluid from one passage to the other via the cavity is permitted or precluded in dependence upon the energization state of the pole pieces.

6. A valve unit as in claim in which a capillary passage within the valve body provides a continuous by-pass connection between the two flow passages.

7. A valve unit as in claim 4 in which a second pair of flow passages controlled by the opposite ends of the reed-valve enter the cavity on the side thereof opposite the first pair of flow passages whereby flow of fluid via the cavity between the first pair of passages or between the second pair of passages is dependent upon the energization state of the pole pieces.

8. A valve unit as in claim 7 in which the passages of each pair is connected within the valve body by a capillary by-pass for the cavity.

9. A valve unit as in claim 4 additionally including sealing means for isolating cavity sections in which the free ends of the reed-valve are respectively disposed, and

in which each of the isolated cavity sections has extending therefrom through the valve body a flow passage out of the path of the reed-valve.

10. A valve unit as in claim 9 in which at least one of the isolated cavity sections has two flow passages entering it on opposite sides of the free end of the reed-valve and in the path thereof, and

a third flow passage entering it out of the path of said free end for communication with one or the other of said two flow passages depending upon which of them is closed by the reed-valve.

11. A valve unit as in claim 4 in which at least one capillary passage within the body blocks provides a continuous by-pass connection of fixed cross-sectional area between two of the flow passages.

12. A valve unit comprising a pair of blocks sealed face-to-face and at least one of which is recessed to form an elongated isolated sampling cavity,

a first pair of flow passages extending through one of said blocks to opposite ends of said cavity,

a second pair of flow passages extending through the other of said blocks and respectively entering the cavity on the side opposite one of said first pair of flow passages,

a reed-valve fastened intermediate its ends to one of said blocks with its ends flexed to close one pair of passages, and

actuating means for said reed-valve including magnetic pole pieces extending to the cavity and respectively adjacent the free ends of said reed-valve.

References Cited UNITED STATES PATENTS 1,282,275 Morris 251-129 1,394,615 10/1921 Erwin 137-559 2,575,086 11/1951 AtChiSOn 251- 2,635,632 4/1953 Mayer 251-65 2,687,169 8/1954 Maurice 137-609 2,887,255 5/1959 Bauerlein 222-504 2,938,703 5/ 1960 DietZ 251-129 3,017,772 1/1962 \Vright 73-422 3,021,713 2/1962 Wright 73-23.1 3,102,712 9/1963 Zilk 251-298 3,181,559 5/1965 Hipple 137-489 3,208,467 9/1965 Eichelman 251-75 FOREIGN PATENTS 1,008,888 6/1963 Great Britain.

WILLIAM F. ODEA, Primary Examiner.

D. H. LAMBERT, Assistant Examiner.