US 3667489 A
A pure fluid device for providing efficient digital operation. A laminar input stream is caused to interact with one or more control streams within a confined interaction chamber to provide a binary output pressure whose level depends upon the laminar or turbulent condition of flow within the chamber. The invention provides extremely rapid switching in a precisely controllable manner. The invention is also operable to provide controllable proportional amplification by producing an output pressure of a magnitude variable in response to control pressure variation.
Description (OCR text may contain errors)
United States Patent 1 3,667,489
Blaiklock et a1.  June 6, 1972  PURE FLUID DEVICE 3,469,593 9/1969 O'Keefe ..l37/81.5
172] Inventors: Paul M. Blaiklock, Newton Centre; Hansggti Diem Khmer Duxbury bmh Mass 3:51 1:256 5/1970 Ab1er.:::::::::::: .:::137/81:5
 Assignee: Fluidic Industries, Inc., l-lingham, Mass.
 Filed: Jan. 12, 1970 21 Appl. No.: 2,297
52 us. Cl ..137 s1.s
 Int. Cl. ..Fl5c 1/18  Field ofSearchm; ..l37/8l.5;235/20l  References Cited UNITED STATES PATENTS 7 3,187,763 6/1965 Adams ..l37/8l.5 3,272,214 9/1966 Warren.. ...,137/8l.5 3,362,421 1/1968 Schaffer.... ....l37/81.5 3,452,767 7/1969 Posmgies ..137/81.5
Primary Examiner-Samuel Scott Attorney-Joseph Weingarten  ABSTRACT A pure fluid device for providing efficient digital operation. A laminar input stream is caused to interact with one or more control streams within a confined interaction chamber to provide a binary output pressure whose level depends upon the laminar or turbulent condition of flow within the chamber. The invention provides extremely rapid switching in a precisely controllable manner. The invention is also operable to provide controllable proportional amplification by producing an output pressure of a magnitude variable in response to control pressure variation.
8 Claims, 13 Drawing Figures PATENTEDJUN 6 1912 SHEET 1 BF 4 FIG. I
PRIOR ART DEVICE INVENTORS 6H PAUL M. BLAlKlfilglg I y ANs-D| K1 '2 CONTROL PRESSURE (INS. OF WATER) ATTOR EYS Amm. m0 wz: mmDmwmma PDnZbO 11 r 4 i i PATENTEDJUH s 1972 3, 67, 489
SHEET 2 or 4 I04 2 I04 I07 I05 I07 FIG. 4A FIG. 4B 8 v E J LL] 5 g U) z I 5 28 FIG. 9 E CL D O. D O
-o.5 00 0.5 lb H5 2b CONTROL PRESSURE INVENTORS (INS. OF WATER) PAUL M. BLAIKLOCK BY HANS-DI R K|NNER ATTOR YS PATENTEDJUN 5 I972 SHEET 3 OF 4 -j INVENTORS PAUL-M. BLAIKLOCK H Wm K 2%,.
ATTOR EYS INNER PATENTEUJUN 6 I972 3.667, 489
sum 0F 4 OUTPUT PRESSURE (INS. OF WATER) ix CONTROL PRESSURE (ms. OF WATER) SET INPUTS OOI I T OUTPUT INVENTORS PAUL M. BLAIKLOCK BY HANS-DI TER KINNER ATTORN YS FIG. I2
PURE FLUID DEVICE FIELD OF THE INVENTION This invention relates to fluidic devices and more particularly to pure fluid devices employing laminar flow.
BACKGROUND OF THE INVENTION Pure fluid devices are known in which fluid streams are employed for control purposes in many applications. Such devices can be incorporated into networks and systems much like their electronic counterparts to provide intended indication, control and logic functions. One class of pure fluid devices, utilizes the controlled interaction of a control stream and a laminar fluid power stream to provide pneumatic control without moving parts. In general, a laminar fluid power stream is directed from the orifice of a supply tube through an unconfined space toward the orifice of a collector tube, with a control tube arranged in the unconfined space and adapted to ,direct a control stream into interaction with the power stream.
In the absence of a control stream, the power stream reaches the collector tube in a laminar condition. When, however, the control stream is applied with predetermined flow to the power stream, the power stream changes from a laminar t turbulent condition, with the result that the pressure in the collector tube is reduced from that existing under laminar flow conditions. The difference in pressure in the collector tube can be employed to represent binary device states for digital control purposes. Moreover, the change in pressure in the collector tube caused by the change in the power stream from laminar to turbulent flow can be greater than the change in pressure applied to the control stream to effect alteration of the power stream flow condition, and, thus, amplification can be provided.
However, devices of known construction do not ofier predictable or precisely controllable operation sufficient for many purposes. For example, when employed to provide proportional amplification, conventional turbulence amplifiers require extremely critical control of the pressure of the control stream to achieve intended pressure variation in the device output, such critical control not being usually achievable in practical operating environments. This same deficiency of control precision also causes unreliable and often imprecise digital device operation, thereby limiting the utility of such conventional devices in fluidic logic systems.
SUMMARY OF THE INVENTION In accordance with the present invention a pure fluid device is provided in which efficient and precisely controllable digital operation is achieved, in addition to controllable proportional amplification. The invention utilizes the transition from a laminar flow condition to one of turbulent flow and accomplishes such transition by means of a shaped confined interaction chamber which is effective to permit improved device operation.
In brief, the novel device includes an input passage or tube adapted to establish and maintain laminar flow and communicating with a shaped confined interaction chamber which, in turn, communicates with a shielded region vented to the working atmosphere. The use of a laminar flow stream provides a considerable advantage over conventional turbulence devices. For example, the invention utilizes very low input and control pressures and does not exhibit any appreciable suction as in turbulence devices. One or more control passages are coupled to the interaction chamber and each is operative to direct a low energy control stream into intersection with a laminar input stream flowing therethrough. An output passage is disposed on a common axis with the input passage and communicates with the open region. In the absence of a control stream, the input stream flows laminarly through the interaction chamber and the adjacent shielded region to the output passage, giving rise to a relatively high output pressure therein. When a control stream is directed into intersecu'on with the laminar input stream, the input stream undergoes a transition from a laminar to a turbulent state, resulting in a predetermined decrease in output pressure. The relatively higher and lower output pressures can provide intended binary output states.
The invention is operative in either of two modes of operation, one mode providing effective binary operation, while theother mode provides improved linear amplification. For binary operation, the shaped interaction chamber includes means for providing fluid feedback therein in a manner operative to achieve extremely rapid switching from one state to another. For linear operation, such feedback means are not necessary and the confined interaction chamber provides a controlled laminar jet deflection and distortion to achieve markedly improved amplifier operation.
DESCRIPTION OF THE DRAMNGS The invention will be more fully understood from the following detailed description, taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a plan view of a fluid device embodying the invention;
FIG. 2 is a sectional elevation view of the embodiment of FIG. 1;
FIG. 3 is a plot of output pressure versus control pressure useful in comparing digital operation of the invention and operation of a prior art turbulence amplifier;
FIGS. 4A and 4B are sectional elevational views of alternative implementations of the embodiment of FIG. 1;
FIG. 5 is a sectional elevation view of an alternative implementation of the device of FIG. 1;
FIG. 6 is a plan view of a portion of the device formed in plate 42 of FIG. 4;
FIG. 7 is a plan view of a further embodiment of the invention;
FIG. 8 is a plot of output pressure versus control pressure useful in illustrating the proportional amplifier characteristics of the invention, with a control jet applied via port 31a;
FIG. 9 is a partly cut-away plan view of an alternative implementation of the embodiment of FIG. 7;
FIG. 10 is a plot of output pressure versus control pressure useful in illustrating the proportional amplifier characteristics of the embodiment of FIG. 7, with a control jet applied via port 24;
FIG. 11 is a schematic representation of a flip-flop utilizing the invention; and
FIG. 12 is a schematic representation of an AND gate utilizing the invention.
DETAILED DESCRIPTION OF THE INVENTION A fluid device according to the invention is illustrated in FIGS. 1 and 2 and includes an input tube 10 having an orifice 25 communicating with a shaped confined interaction chamber which includes an interaction region 12 and a contiguous shaped region 14. A collector or output tube 16 is disposed on a common axis with input tube 10, the orifice 18 of output tube 16 communicating with a shielded region 20 which is vented to the working atmosphere. Region 20 is shaped as illustrated to provide a large area vented zone; the particular shape is not especially critical. The top and bottom walls 11 and 13 of region 12 are substantially parallel and are coplanar with input tube 10. That is, input tube 10 is of a diameter which is equal to and in alignment with walls 11, and 13, as seen in FIG. 2. The side walls 19 and 21 of region 12 are substantially parallel and are outwardly disposed from tube ing from input tube through zone 12. In the illustrated embodiment, eight control tubes 22 are shown and some or all of these control tubes can be used for interconnecting other fluidic devices to form predetermined logical network configurations, as will be described. For many purposes only a single control tube is required, and of course the invention can be implemented with a single control tube for these purposes.
A pair of ports 24 are disposed in communication with the input end of interaction zone 12 adjacent the input orifice 25 of input tube 10 and are operative to vent the interaction zone to prevent suction on the control ports when the input stream is in turbulent condition. A port 29 is provided for each control tube 22 for supply of fluid thereto, while an output port 33 is provided for output tube 16 to couple the output stream to utilization means. An input port (not shown) is provided to supply fluid to input tube 10. The shaped region 14 includes side walls 26 which flare outwardly from zone 12 and which continue at the same flare angle to define the side walls 27 of zone 20. Region 14 includes a channel 28 in respective upper and lower walls 34 and 35 and having substantially the same width as the width of zone 12 and which extends along the axis of the device to a point slightly less than the full length of region 14 to define a respective thin rib or knife edge 30. As seen in FIG. 2, the walls 34 and 35 of region 14 are outwardly disposed and parallel to the respective walls 13 and 11 of region l2. Ribs 30 have confronting surfaces which are removed from the planes of the walls 11 and 13 by an amount to prevent interference with the laminar flow of the input stream in the absence of control pressure.
The invention is illustrated in greatly enlarged form, actual devices being generally of rather small size. For example, a device of the type shown in FIG. 1 typically has input and output tubes of 0.0l75 inch diameter and an interaction chamber of 0.34 inch in length. The device can be fabricated for example by machining of etching individual elements into respective upper and lower plateswhich can be secured together to provide a completed fluid device therein. For example, the device according to the invention, as seen in FIG. 2, is formed within first and second plates and 17 of metal or other suitable material. The fluid tubes are usually configured of semicircular cross section in each plate so that when the plates are secured together, a substantially circular cross section fluid tube is provided for efficient fluid flow. Alternatively a square fluid tube cross section can be employed. The device configuration formed in each plate is identical, with the exception of the fluid supply ports and vents, which are usually formed in a single plate. For many purposes, a plurality of devices are formed as a single structure to provide a complete operational network or system.
Input tube 10 is of a length and diameter to establish and maintain a fluid stream in laminar flow therein such that a laminar stream will emerge from orifice and flow through regions 12, 14 and 20 and be received by collector tube 16 substantially in laminar condition, in the absence of any control stream applied by one or more control tubes 22. The laminar fluid stream touches the top and bottom walls 11 and 13 of of region 12 as it flows therethrough. The control stream has a lesser flow and lesser pressure than the input stream and is usually in laminar flow. Typically, supply pressures of less than 1.5 psi and control pressures of less than 0.1 psi are employed.
With application of a control stream from a control tube 22, the supply stream deflects and distorts by reason of the momentum of the control flow and pressure build-up in the confined region 12. The distorted supply stream flowing in region 14 engages the knife edges which act as a source of disturbance to cause the stream to rapidly become turbulent. The turbulent stream tends to reflect ofi knife edges 30 and recirculate back through channel 28 toward zone 12, this recirculation causing an avalanche or positive feedback effect which is operative to cause transition from laminar to turbulent flow in an extremely short time interval. The pressure within collector tube 16 drops markedly when the supply stream becomes turbulent, this pressure drop indicating a change in the device state. The device thus acts in a binary manner to provide one of two output levels depending upon the presence or absence of a control jet which governs whether the fluid stream flow is laminar or turbulent.
It is a particular feature of the invention that the transition between laminar and turbulent flow is achieved in an extremely short time interval. Moreover, the pressure in collector tube 16 when the supply stream is turbulent, is at a lower pressure than usually obtainable by conventional devices. Thus, the invention provides a fluid device having markedly improved switching characteristics.
The switching performance of the invention is shown in the graph of FIG. 3 in which the solid curve depicts the output pressure in the collector tube of the device as a function of control pressure in the control tube. It is evident that the output pressure remains substantially constantuntil the controlv pressure is approximately 0.4 inches of water. A slight further increase in control pressure causes the indicated rapid decrease in output pressure, a minimum output pressure of 0.2 inches of water typically being achieved. It will be noted that the cut-off characteristics of the device are extremely sharp and relatively low residual output pressure is achieved. In contrast, the dotted curve illustrates the typical response of a turbulence amplifier of conventional construction and it is seen that there is a relatively gradual variation in output pressure with relatively large changes in control pressure. As a result, such conventional devices exhibit poor cut-off characteristics and a generally higher minimum output pressure.
The rib or knife edge 30 is but one form of obstruction operative in accordance with the principles of the invention to provide rapid switching characteristics. In some instances, the obstruction provided at the downstream end of region 14 is alone sufiicient to provide the intended fluid feedback without channels 28. For example, a rib can be provided across the full width of region 14.
Another example of an obstruction employed to accomplish intended device operation is shown in FIG. 4A which is an end view of a device of the type shown in FIG. 1 as viewed from region 20 toward input tube 10. Walls and 101 are disposed transversely of the device between regions 14 and 20, with a slit 102 therebetween extending between the top and bottom walls and having a width approximately equal to the diameter of orifice 103 of input tube 10 and in alignment therewith. Vertical slits 104 can also be provided adjacent the other ends of walls 100 and 101 to provide suitable venting of region 14. A variation of the feedback obstruction is illustrated in FIG. 4B and includes a square aperture 105 formed in a tranversely disposed wall 106 and in alignment with orifice 103 of the input tube 10. Vent slits 107 are provided as above. In operation, laminar stream flows through region 14 and, in the absence of a control stream applied to one or more of the control tubes, the laminar stream passes through the aperture provided in the transverse wall, to be received by the output tube. Upon application of a control stream, the laminar stream is deflected and/or distorted into impinging relationship with the transverse wall, causing turbulence in the stream and causing recirculation of fluid back toward region 12. As a result of the fluid feedback, the laminar stream rapidly becomes turbulent thereby causing a correspondingly rapid decrease in output pressure in the output tube.
An alternative implementation of the invention is illustrated in FIGS. 5 and 6 in which the novel device is constructed in four plates which can be combined in a laminated package to form a complete device. The device configuration is as shown in FIG. 1 and is substantially symmetrical. For purposes of clarity only two plates are shown, the other two plates being substantially the same. As seen in FIG. 5, plate 40 has formed therein half of supply tube 10 (FIG. 1) and half of collector tube 16. The semicircular portions of the orifices 21 of control tubes 22 are seen in the illustrated cross section. A similar tube configuration is formed in another plate (not shown) which is disposed in confronting relationship with plate 40 to provide the completed fluid tube structure and interaction zone 12. A plate 42 has formed therein the shaped region 14 and is placed in contact with plate 40, as illustrated, together with a like pair of plates to form the device. A plan view of plate 42 is depicted in FIG. 5 and includes the uniquely shaped region 14, region 20, ports 25 which communicate with vents 24 formed within plate 40, and ports 27 which provide inlet and outlet ports for the control tubes 22 formed in plate 40.
The invention can also be employed in a slightly different configuration to provide improved proportional amplification. In this mode of operation, the shaped region 14 (FIG. 1) is not employed. As seen in FIG. 7, the novel device is-similar to the device of FIG. 1 except that the region 41 disposed between interaction zone 12 and output tube 16 is a shielded region which is vented to the working atmosphere. For proportional operation, a pair of control tubes 22a are usually employed, with each disposed on a respective opposite side of interaction zone 12, and coupled to respective control ports 31a for introduction of a suitable supply of control fluid. The control tubes 220 preferably communicate with interaction zone 12 at positions near the input orifice of supply tube 10.
The device in the illustrated configuration operates as a high gain low noise proportional amplifier and exhibits a typical operating characteristic as shown in FIG. 8. As described hereinabove, a supply stream is provided and maintained within supply tube in laminar flow condition and the laminar stream flows through interaction region 12 and thence through zone 41 to the collector orifice 18 of output tube 16. A low pressure control stream enters the communication region 12 via one of control tubes 22a and causes deflection of the laminar stream flowing through region 12 by pressure build-up in the interaction region. The laminar stream is thereby deflected away from output orifice 18 causing a controlled decrease in output pressure which is proportionally related to the magnitude of the control pressure. By introducing a control pressure to each control port 31a, deflection of the laminar stream can be accomplished in an amount related to the difference between the two control pressures.
As seen'in FIG. 8, the novel fluid amplifier provides an output pressure which is directly proportional to an applied control pressure and which is precisely and controllably variable in response thereto. Relatively large changes in output pressure can thereby be provided in response to relatively small variations in control pressure. Conventional turbulence amplifiers cannot be easily employed in many applications requiring controlled proportional amplification, since significant output variation, in addition to noise, occurs for extreme ly small changes in control pressure and a degree of control is required which is not easily achievable in practice.
As an alternative implementation of the embodiment of FIG. 7, the control tubes 220 can be eliminated, and control streams introduced into region 12 via ports 24. Of course in this embodiment, ports 24 would be coupled to a source of control pressure, rather than being vented as in the embodiments described hereinbefore. Operation is substantially as described above, wherein a pressure build-up within region 12, caused by application of a control stream, causes deflection of the laminar input stream away from the side of increased pressure. Variation in output pressure can be detected by a single output tube 16, as in FIG. 7, or by a pair of displaced output tubes 48 and 49, as in FIG. 9. Output tubes 48 and 49 are disposed on respective opposite sides of the longitudinal axis of the device along which the laminar stream flows, and are coupled to respective output ports 51. Proportional operation of the device of FIG. 7 with the control, stream applied via port 24 is depicted in FIG. 10. It should evident that high gain, low noise amplification is provided.
stream, the input stream remaining substantially in laminar flow. Flow of the control stream on one side of interaction region 12 causes a pressure build-up which in turn causes deflection of the laminar input stream away from the region of increased pressure. A differential output pressure is provided in output tubes 48 and 49, a decrease in output pressure being experienced by the output tube away from which the laminar stream is deflected, while a corresponding pressure increase is experienced by the output tube toward which the laminar stream is deflected. As discussed above, a control stream can be introduced to both control ports 24 to cause stream deflection in an amount proportional to the difference between the applied control pressures. For certain applications, it is desirable to use a differential output configuration such as provided by the device of FIG. 9, while for other purposes a single output configuration is preferable, as in FIG. 7. For some purposes, a single output may be offset from the longitudinal device axis. In the case of an offset output tube configuration, the amplifier gain will be of a sense dependent upon the direction of offset. The control pressure applied to ports 24 can be both positive and negative and proportional amplification can be provided with either sense of control pressure as seen from FIG. 10.
The invention in its digital mode of operation can be embodied in a variety of logical configurations to suit particular operating requirements. Referring to FIG. 1 1, there is shown a flip flop comprised of two fluid devices and constructed according to the invention. First and second fluid devices 50 and 52 are provided, each having its output tube coupled to a control tube of the opposite device. More particularly, output tube 54 is coupled to control tube 56 of device 52, while output tube 58 is coupled to control tube 60 of device 50. The supply tubes 62 and 64 are connected to a common source of supply pressure. A second control tube 66 of device 50 is coupled to a source of control signalsto provide a SET input, while control tube 68 of device 52 is coupled to a source of control signals to provide a RESET input. It will be appreciated that the fluid flip flop circuit exhibits two bistable states, one wherein output A is at a higher pressure level than output B, and vice versa. Once a given bistable state is established, the device will remain in that state until switched to the opposite state by energization of an appropriate SET or RESET control jet. In operation, with a laminar fluid stream flowing from supply tubes 62 and 64 and a control stream applied via control tube 66, the pressure in output tube 54 will drop due to the transition from laminar to turbulent flow according to the invention, resulting in a relatively higher pressure level by reason of the laminar flow of the input stream through the interaction zone of device 52, and this higher pressure flow is coupled from output tube 58 to control tube 60 of device 50 to maintain output A in its low level state even after the SET control signal is removed. When, however, a RESET control signal is applied to control tube 68, causing the transition from laminar to turbulent flow in device 52, the output pressure in output tube 58 markedly drops to provide a relatively lower pressure output B. The drop in pressure in collector tube 58 also causes a corresponding drop in pressure in control tube 60, causing the turbulent flow therein to revert to a laminar condition, with consequent increase in the output pressure in tube 54. The higher pressure flow in tube 54 is coupled tocontrol tube 56 to maintain device 52 in its low level state after removal of the RESET control signal. The invention as embodied in an AND gate is illustrated in FIG. 12 and includes four fluid devices, each constructed as described hereinabove and each having a respective supply tube 70, 72, 74 and 76 coupled to a common source of supply fluid. The
i respective output tubes 78, 80, 82 and 84 of the fluid devices are coupled to respective control tubes 86 of a fluid device 88, the collector 90 of which provides the gate output. The supply tube 92 of device 88 is also coupled to the common source of supply fluid. A control tube 94 of respective devices is coupled to respective input ports labeled C, D, E and F. In opera tion, a relatively higher pressure output will be provided at output tube 90 when control streams are applied to all four input tubes, while the output will be at relatively lower pressure for all other input conditions. With control streams supplied to the four input tubes C, D, E and F, the respective fluid devices will switch to the turbulent state wherein a lower pressure output stream is provided. The four control tubes 86 of device 88 are therefore essentially inactive with the result that the output pressure in output tube 90 is at a relatively higher level. With the removal of one or more of the input control streams, those devices for which the control stream is removed will revert to a condition of laminar flow, according to the invention, causing a higher pressure output to appear at the output tube of the aforesaid device, which will energize selected ones of control tubes 86, which, in turn, will cause device 88 to revert to turbulent flow, causing a decrease in pressure in output tube 90. In this manner a first digital output state is provided in the presence of all four input control streams, and a second digital output state is provided for all other input conditions, thereby implementing the logical AND function.
Various modifications and implementations will occur to those versed in the art and it is not intended to limit the invention by what has been particularly shown and described.
A pure fluid device comprising:
a confined interaction chamber having top and bottom walls and a pair of side walls;
an input passage having an orifice communicating with one end of said interaction chamber and adapted to establish and maintain a fluid stream in laminar flow through said chamber;
a control passage having an orifice communicating with said chamber and adapted to introduce a low energy control stream into said chamber;
a shielded region contiguous with said interaction chamber and vented to the working atmosphere; and
an output passage having an orifice disposed at the downstream end of said shielded region;
said output passage being operative to provide a predetermined output pressure in response to a laminar stream received from said input passage in the absence of a control stream, and to provide a predetermined different output pressure in the presence of a control stream;
said confined interaction chamber including a confined region having top and bottom walls substantially parallel and coplanar with said input passage, and substantially parallel side walls outwardly disposed from said input passage, said control passage communicating with said confined region; and
a shaped region disposed downstream of said confined region and contiguous therewith, said shaped region having top and bottom walls disposed outwardly of the respective top and bottom walls of said confined region, and means for providing recirculation of said fluid stream within said shaped region in the presence of a control stream to achieve rapid switching from one binary state to another;
said recirculation means including a channel formed in the top and bottom walls of said shaped region and extending parallel to the axis thereof; and
a rib disposed at the downstream end of each of said channels across the width thereof and extending inwardly by an amount to permit unobstructed flow of said laminar stream from said input passage in the absence of a control stream and to engage a portion of said laminar stream in the presence of said control stream.
2. A pure fluid device according to claim 1 wherein said channels are each of a width substantially equal to the separation between the side walls of said confined region.
3. A pure fluid device comprising:
a confined interaction chamber including a confined region having top and bottom walls and a pair of side walls, and a shaped region disposed downstream of said confined region and contiguous therewith; said shaped region having top and bottom walls disposed outwardly of the respective top and bottom walls of said confined region, and means disposed at the downstream end of said shaped region for providing recirculation of said fluid stream within said shaped region in the presence of a control stream to achieve rapid switching from one binary state to another;
an input passage having an orifice communicating with one end of said interaction chamber and adapted to establish and maintain a fluid stream in laminar flow through said chamber;
a control passage having an orifice communicating with one of said side walls of said chamber and adapted to introduce a low energy control stream into said chamber;
said top and bottom walls of said confined region being substantially parallel and coplanar with said input passage, and said side walls being substantially parallel and outwardly disposed from said input passage;
a shielded region contiguous with said interaction chamber and having side walls outwardly disposed from said input passage and top and bottom surfaces fully vented to the working atmosphere; and
an output passage having an orifice disposed at the downstream end of said shielded region;
said output passage being operative to provide a predetermined output pressure in response to a laminar stream received from said input passage in the absence of a control stream, and to provide a predetermined different output pressure in the presence of a control stream.
4. A pure fluid device according to claim 3 wherein said recirculation means includes an obstruction disposed in said shaped region in an operative position to permit passage of a laminar stream from said input passage in the absence of a control stream and to engage a portion of said laminar stream in the presence of a control stream.
5. A pure fluid device according to claim 3 wherein said recirculation means includes a wall disposed at the downstream end of said shaped region and transversely thereacross;
an aperture formed in said wall in alignment with the orifice of said input passage; and
means for venting said shaped region.
6. A pure fluid device according to claim 3 wherein said recirculation means includes a channel formed in the top and bottom walls of said shaped region and extending parallel to the axis thereof; and
an obstructing element disposed at the downstream end of each of said channels across the width thereof and extending inwardly by an amount to permit unobstructed flow of said laminar stream from said input passage in the absence of a control stream and to engage a portion of said laminar stream in the presence of said control stream.
7. A pure fluid device according to claim 3 wherein said recirculation means includes an obstructing element disposed at the downstream end of said shaped region across the width thereof and extending inwardly by an amount to permit unobstructed flow of said laminar stream from said input passage in the absence of a control stream and to engage a portion of said laminar stream in the presence of said control stream.
8. A pure fluid device according to claim 3 wherein said confined region includes one or more vents communicating between the input end of said confined region adjacent said input passage and the working atmosphere.