US3500852A - Pure fluid amplifier having a stable undeflected power stream - Google Patents

Description

March 17, 1970 P. BAU 3,500,852

PURE FLUID AMPLIFIER HAVIN STABLE UNDEFLECTED POWER STREAM Filed Feb. '2, 1968 INVENTOR PETER BQUE R ATTORNEYS United States Patent 3,500,852 PURE FLUID AMPLIFIER HAVING A STABLE UNDIEFLECTED POWER STREAM Peter Bauer, Germantown, Md., assignor to Bowles Engineering Corporation, Silver Spring, Md., a corporation of Maryland Filed Feb. 7, 1968, Ser. No. 703,659 Int. Cl. F15c 1/14 US. Cl. 137--81.5 15 Claims ABSTRACT OF THE DISCLOSURE A pure fluid amplifier has at least one stable state in which its power stream is undefiected. The stable undefiected power stream is formed from two parallel spaced streams issuing into the amplifier interaction region from two nozzles in sufliciently close proximity that mutual entrainment between the streams greatly reduces the pressure between the stream relative to the regions on the other sides of the streams and causes them to merge downstream of the nozzles, stabilizing in a central position regardless of the sidewall effects. The wall surface between the nozzles is blunt rather than streamlined to enhance initial separation of the streams and faster mutual entrainment of fluid between the streams.

BACKGROUND OF THE INVENTION The present invention relates to pure fluid amplifiers having at least one stable state and more particularly to a technique for providing a stable position for a power stream in a fluid amplifier without requiring a surface to which the stream may attach.

It is known to provide fluid amplifiers with stable states or conditions by utilizing the boundary layer wall attachment phenomenon. This phenomenon is responsible for etfecting attachment of a fluid stream to a wall and results from the entrainment of fluid by the stream from the space between the stream and the wall, thereby reducing the pressure and causing the stream to be deflected toward and become attached to the wall. In pure fluid amplifiers utilizing this phenomenon, stable power stream conditions are characterized by location of the amplifier interaction region sidewalls, such that positions of the power stream intermediate the two sidewalls are considered unstable. It is possible to design a pure fluid amplifier in which the interaction region sdewalls are sufliciently removed from the power nozzle or diverge sufficiently therefrom so that an unperturbed power stream issuing from the power nozzle will not lock-on to the sidewalls; rather, lock-on in such an amplifier will be achieved only if some perturbation or deflecting force acts on the power stream. However, devices such as these are extremely sensitive to power stream noise, shock and vibration whereupon the deflected power stream position is rendered quite unstable. Also, the lock-on is not very stable and minor changes in load cause the streams to become detached.

In some applications of fluid amplifiers it is necessary to provide power stream stability for power stream positions not corresponding to attachment of the power stream to the sidewalls. For example, a tri-stable pure fluid amplifier may have two stable states in which the power stream attaches to one or the other of the respective sidewalls, and a third state for which no sidewall is available to provide stability. Further, it is also desirable in many cases for proportional pure fluid amplifiers to have a stable undefiected power stream which is not substantially affected by noise, shock or vibration.

In my prior US. Patent No. 3,192,938 I disclose a device having an oval-shaped interaction chamber with which three outlet passages communicate at its downstream end. Two of the outlet passages received fluid when the power stream was locked-on to one or the other of the sidewalls respectively in the interaction region. The third outlet passage received fluid when the power stream was undefiected and issued through the center of the interaction region. The problem with this device was the sensitivity of the power stream to external perturbations such as produced by shock and noise that tended to deflect the power stream and cause it to lock-on to one or the other sidewalls of the oval-shaped interaction region. In addition, fluctuations in power stream pressure produced problems in that a predetermined power stream pressure had to be maintained in order to prevent the power stream from being deflected merely by unintentional minute asymmetries within the interaction region.

A subsequent attempt to achieve power stream stability by other than boundary layer wall attachment techniques is exemplified by the US. Patent No. 3,181,545 to F. E. Murphy, Jr. In the Murphy pure fluid amplifier a foil or fin is placed downstream of the power nozzle in the interaction region, the power stream locking on to the fin or air-foil in accordance with well-known aerodynamic principles to provide a stable condition for the power stream without utilizing an interaction region sidewall. Specifically, the power stream in the Murphy device follows the stream line configuration on both sides of the symmetric foil, thereby changing the length of the flow path of fluid in the power stream immediately adjacent the foil. This increases the velocity in the fluid immediately adjacent the foil surface and produces a concomitant decrease in pressure therein. As a result of the pressure decrease in fluid at the foil surface on both sides of the foil, the power stream attached to the foil to provide a stable state for the amplifier. The Murphy device provides stability for the power stream in positions other than power stream attachment to the sidewalls; however, this is achieved in the Murphy device at the expense of pressure recovery. Specifically, the presence of the foil in the path of the power stream tends to increase turbulence in the power stream downstream of and adjacent the foil and thereby reduces the efficiency of the pressure recovery of the device. In addition, the Murphy technique is not suitable for utilization in proportional type pure fluid amplifiers due to inherent hysteresis eiiects associated with power stream lockonto the fin or foil. Specifically, a predetermined pressure differential is required across the power stream of the Murphy device before lock-on to the foil can be destroyed. However, pressure difierentials lower than the predetermined pressure ditferential, when applied across a power stream which is initially in some position other than that in which it is locked-on to the foil, do not produce lock-on to the foil but rather deflect the stream relative thereto.

It is an object of the present invention to provide power stream stability in fluid amplifiers without utilizing boundary layer lock-on techniques, wherein the power stream position is insensitive to environmental disturbances, and without sacrificing amplifier pressure recovery.

It is another object of the present invention to provide an improved tri-stable pure fluid amplifier in which two stable states are achieved by conventional boundary layer techniques and in which a third stable condition is achieved by effectively producing a boundary layer bubble in free space.

It is still another object of the present invention to provide a pure fluid amplifier of the proportional type in which the undefiected position of the power stream is insensitive to noise and other extraneous disturbances.

SUMMARY OF THE INVENTION In accordance with the present invention a pair of parallel adjacent streams are issued into the upstream end of a fluid amplifier interaction region in sufliciently close proximity to produce mutual entrainment of fluid between the two streams. The pressure between the streams is quite low and consequently the streams merge to form a single stable power stream which may be utilized in fluid amplifier switching configurations of the monostable, bistable or tri-stable type, or alternatively in a proportional type pure fluid amplifier. In the preferred disclosed embodiments of the present invention the two streams are issued from respective nozzles communicating with the upstream end of the interaction region, the nozzles being separated by a blunt wall surface. The space immediately downstream of the wall surface between the two power streams is partially evacuated by the entrainment of fluid therefrom by both of the streams so that the streams may be effectively drawn together. In effect each stream performs the function of an interaction region sidewall for the other stream, i.e., it defines a surface displaced from the other stream from which fluid is evacuated to form a boundary layer bubble. Since the surface is also a flowing stream, evacuation of fluid from between the streams is highly eflicient and the lock-on of one stream to the other is quite strong so that deflection of the joined stream does not produce separation of the streams downstream of their confluence.

BRIEF DESCRIPTION OF THE DRAWINGS The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawing, wherein:

FIGURE 1 is a plan view of a tri-stable element constructed in accordance with the principles of the present invention; and

FIGURE 2 is a plan view of a proportional pure fluid amplifier constructed in accordance with the principles of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGURE 1 of the accompanying drawings for a more complete understanding of the present invention, there is illustrated a pure fluid amplifier of the conventional boundary layer type. The passages, cavities and nozzles required to form amplifier 10 are preferably etched, molded or otherwise formed in a flat plate 11 which is sandwiched and sealed between a pair of flat plates 12 and 13 by any conventional means such as machine screws or adhesives. A power nozzle 14 formed in plate 11 has a flow divider 15 disposed within its throat. The upstream end of flow divider 15 is substantially wedge or V-shaped in order to facilitate flow around the sides of the divider. The sides of flow-divider 15 are substantially parallel and, in conjunction with respective inwardly converging sides of nozzle 14, define distinct left and right nozzles 17, 19 adapted to issue two respective streams of fluid into interaction region 21 of amplifier 10. The downstream end of flow divider 15 defines the upstream end of interaction chamber 21 and is substantially flat and generally perpendicular to the sides of flow divider 15.

In the particular embodiment illustrated in FIGURE 1, flow divider 15 is centrally disposed within power nozzle 14 so that the two nozzles 17 and 19 defined by flow divider 15 and the walls of power nozzle 14 are substantially identical in size and configuration. Left and right sidewalls 23 and 25 of interaction region 21 are positioned sufficiently proximate respective left and right nozzles 17 and 19 so that boundary layer effects are developed between these sidewalls and the streams issued by the respective nozzles. Communicating with interaction region 21 through respective sidewalls 23 and 25 are a pair of left control nozzles 27 and 29 and right control nozzles 31 and 33 respectively. The control nozzles are adapted to receive respective control signals for deflecting the resultant power stream issued from power nozzles 17 and 19. l

Communicating with the downstream end of interaction region 21 is a left output passage 35 adapted to receive resultant power stream fluid when the power stream attaches to left sidewall 23, a right output passage 39 adapted to receive the resultant power stream when it attaches to right sidewall 25, and a central output passage 37 disposed between passages 35 and 39 and adapted to receive the resultant power stream when directed generally centrally of interaction region 21. Left and right vent passages 41 and 43 communicate with left and right output passages 35 and 39 respectively and serve in a conventional manner to prevent backloading of either of passages 35 or 39 from causing switching of the power stream.

A flow splitter 45 is positioned between left output passage 35 and central output passage 37; another flow splitter 47 is positioned between right output passage 39 and central output passage 37. The upstream ends of flow splitters 45 and 47 are concave, forming cusps which act to peel off a portion of the fluid flowing into any of the output passages. The peeling ofi of fluid creates a vertical flow which is fed back and stabilizes the power stream when directed toward the respective output passages in the manner fully described in US. Patent No. 3,225,780 to R. W. Warren et al.

In operation, the application of pressurized fluid to nozzle 14 results in the issuance of two power streams from respective left and right power nozzles 17 and 19 into interaction region 21. These two power streams merge some distance downstream of flow divider 15 due to mutual entrainment between the streams by evacnation of the fluid between them. As a result of the forces acting to draw the streams together, the merged single stream achieves a stable position in which it is directed centrally of interaction region 21 and out through central output passage 37. The flatness or bluntness of the downstream end of flow divider 15 is instrumental in creating the desired stability of the resultant power stream in its central position since it partially defines a volume immediately downstream of the flow divider 15 between the two streams from which the two streams mutually evacuate fluid. To this extent it is important that the downstream end of flow divider 15 be blunt as opposed to streamlined, the latter configuration serving only to merge two streams but not producing the evacuated space which draws the streams together rather than permitting each stream to be attracted to its adjacent sidewall. It is well known that a power stream issuing into an interaction region with sidewalls would be deflected toward one of the sidewalls. This tendency must be overcome in a tri-stable device and is overcome in the device of the present invention by creating a boundary layer bubble between the two streams having a pressure, due to entrainment from both sides, less than the pressure on the outside of the two streams.

The stability of the resultant power stream when directed toward central output passage 37 is relatively insensitive to pressure variations in the fluid supply nozzle 14 and to shock and vibration experienced in a normal operating environment. The stream in its central position is, however, somewhat more susceptible to deflection by a control signal applied to one of the various control nozzles 27, 29, 31, 33, than is the stream when attached to one of the interaction region sidewalls 23 and 25; that is, there is no boundary layer lock-on to a fixed surface to be overcome by the control signal when the power stream is stably directed toward central output passage 37.

For a device proportioned substantially as illustrated in FIGURE 1, the two power streams from nozzles 17 and 19 initially merge to form a stable power stream directed to central output passage 37, assuming that there is no control signal applied to any of control nozzles 27, 29, 31 and 33. If the combined resultant pressure of the control signals applied to the control nozzles is greater on one side of the resultant stream than the other, for example as would be the case if a control signal were applied to left control nozzle 27 and none of the other control nozzles, the resultant power stream is deflected appropriately, in this case toward right sidewall 25 to which it attaches and is received by right output passage 39. Removal of the signal from control nozzle 27 and application of a subsequent control signal to one of the right control nozzles 31 .or 33, at a sufficient pressure to overcome the boundary layer effects causing attachment of the resultant stream to right sidewall 25, deflects the resultant power stream not to central output passage 37, but to left output passage 35; that is, for the configuration illustrated in FIGURE 1 the boundary layer effect produced between the resultant stream and the left sidewall 23 is sufficient to deflect the power stream past the central output passage 37. Similarly, once the resultant power stream is attached to left sidewall 23, application of a control signal at a pressure suflicient to overcome lock-on to left wall 23 causes deflection of the resultant stream to right output passage 39, the resultant stream attaching to the right sidewall 25. Once the resultant stream has attached to either sidewall 23 or 25 it can readily be returned to its stable position directed towards central output passage 37 only by equal pressures applied across the resultant power stream.

Of course the above described operation can be modified somewhat by changing the configuration of amplifier as desired. Specifically, if it is desired that the power stream be returned to its centrally stable position from a deflected position by one control signal without requiring equal and opposite control signals, modifications in the sidewall configurations can be provided. For example the sidewalls 23 and 25 can be rendered more divergent than illustrated in FIGURE 1 whereby to reduce the effectiveness of the deflecting force of the boundary layer phenomenon and thereby permitting the stream to be effectively stepped from the left to central to right output passages or vice versa by a series of respective applied control pulses. A similar result may be achieved by shortening the length of interaction region 21; that is by moving flow splitters 45 and 47 somewhat closer to power nozzle 14. It will be evident in view of these remarks therefore that various suitable configurations for tristable element 10 may be employed to produce the operation desired.

Amplifier 10 may be provided with a fourth stable state by providing a control port in communication with interaction region 21 through cover plate 12. This additional control port, positioned immediately downstream of divider 15, would be capable of introducing an additional control stream in the evacuated region between the two power streams so as to split the two power streams and cause them to attach to respective opposing sidewalls 23, 25 of interaction region 21. Depending on the configuration of these sidewalls, as discussed above, the split power streams may either remain attached thereto or rejoin upon removal of the additional contfol stream. It the sidewalls 23 and 25 are configured so that the split streams remain attached thereto after the additional control signal is removed, a fourth stable state is achievable which is characterized by simultaneous flow in output passages 35 and 39 and no flow in output passage 37. The stable split streams may be rejoined by applying a control signal to any of control nozzles 27, 29, 31 and 33. It is to be recognized of course that the fourth stable state .of the power stream (when it is split to flow in passages 35 and 39) is characterized by lower output pressure signals at passages 35 and 39 than are present when the entire merged stream is deflected toward these passages.

Referring now to FIGURE 2 of the drawings, there is illustrated a proportional pure fluid amplifier 50 of the stream interaction type. Amplifier 50 is formed in two or three flat plates 51, 52 and 53, or any other configuration for sealing the various passages, cavities and nozzles necessary for a fluid amplifier. Amplifier 50 includes a power nozzle 54 having a flow divider 55, substantially identical to flow divider 15 of amplifier 10 in FIGURE 1, positioned therein to define left and right power nozzles 57 and 59 with respective left and right sidewalls of nozzle 54. Power nozzles 57 and 59 are adapted to issue parallel pressurized streams of fluid into interaction region 61 from the upstream end thereof, the downstream end of divider 55 defining the upstream end of interaction region 61. The left and right sidewalls 63 and 65 of the interaction region 61 are curved away from the orifices of nozzles 57 and 59 so that no boundary layer effects will develop between the power stream and these walls. A pair of left control nozzles 67 and 69 and a pair of right control nozzles 71 and 73 are angularly disposed with respect to the power nozzles 57 and 59 for effecting displacement of the power stream issued therefrom upon application of a control signal to the control nozzle at a sufiicient pressure. Three output passages 75, 77 and 79 communicate from left to right respectively with the downstream end of interaction region 61. The downstream ends of recessed sidewalls 63 and 65 respectively communicate with respective vent passages 81 and 83 formed through plate 52 to provide ambient pressure within interaction region 61 and thereby assuring that boundary layer eflfects will not interfere with proportional operation of the amplifier 50.

As described previously in relation to flow divider 15 of amplifier 10, the presence of flow divider 55 in nozzle 54 produces a pair of parallel power streams, which, when issued into interaction region 61, evacuate fluid from the region therebetween immediately downstream of divider 55 and merge to form a single stable power stream directed centrally of interaction region 61 and towards output passage 77. As is well known in the fluid amplifier art, output passage 77 may either be vented or connected to a suitable utilization device; however, for purposes of the present discussion it will be assumed that output passage 77 is vented and that the differential pressure signal appearing across left and right output passages 75 and 79 is the output signal of interest. In addition, any of control nozzles 67, 69, 71, 73 may be connected to receive a respective input control signal for deflection of the merged power stream. However, for purposes of the present discussion it will be assumed that left control nozzle 69 and right control nozzle 73 are vented to improve the gain of amplifier 50 (as disclosed in US. Patent No. 3,275,013 to John R. Colston) and that appropriate input signals are applied to left control nozzle 67 and right control nozzle 71. In the absence of any differential pressure appearing across nozzles 67 and 71, the merged power stream issues from vent output passage 77. The position of the merged power stream is quite stable under these conditions, and, due to the forces which tend to draw the two individual streams issued from nozzles 57 and 59 together, the merged stream is relatively insensitive to environmental shock, vibration, and noise. Application of a control signal to control nozzle 67 acts to deflect the merged power stream towards output passage 79, the degree of deflection of the merged power stream depending upon the pressure level in the signal applied to control nozzle 67. Similarly a control signal applied to right control nozzle 71 acts to deflect the merged power stream as a function of the signal applied thereto. Thus the overall dilferential pressure applied across control nozzles 67 and 71 produces a resultant deflection of the merged power stream which is manifested by a pressure differential appearing across left and right output passages 75 and 79. In this respect the amplifier 50 operates in a manner quite analogous to prior art proportional fluid amplifiers such as that disclosed in the aforementioned Colston patent. The difference in this proportional amplifier 50, however, resides in the fact that the power stream is substantially more stable and less sensitive to incidental disturbances in its quiescent or undeflected position than is the case in prior art proportional fluid amplifiers. It is clear then that by utilizing the principles of the present invention a proportional pure fluid amplifier can be provided wherein the output signal reflects a function of the input signal with a high degree of accuracy because of the minimization of internally generated noise.

It is to be understood that the configurations illustrated in FIGURES 1 and 2, namely amplifiers 10 and 50, respectively are simply illustrative of the principle underlying the present invention; namely the utilization of a pair of parallel adjacent power streams to form a single stable power stream. Thus the use of a flow divider positioned within a nozzle is not to be construed as limiting since it is evident that a pair of completely independent adjacent power nozzles may be utilized to issue two parallel power streams which merge to form a single stable stream. The advantage of placing the flow divider centrally in nozzle resides in the fact that application of equal pressures to both adjacent nozzles is assured and therefore the single power stream can readily be issued centrally of an interaction region. However, for some applications it may be desirable to have independent nozzles and further, it may be desirable to produce a stable power stream position other than centrally of the interaction region of the amplifier. The latter feature, of course, may be achieved not only through utilization of independent nozzles, but also through positioning a flow divider in a nozzle such that adjacent nozzles of unequal cross-section are formed, whereby the stream issued from the nozzle of larger cross-section tends to draw the other stream towards it rather than itself being drawn towards the stream issued from the smaller nozzle. By this technique it may be seen that the resultant merged stream may be issued in a stable configuration other than centrally of the interaction region.

In addition to the various configurations of the adjacent nozzles described in the preceding paragraph it is also important to understand that the present invention is not limited to a tri-stable or proportional fluid amplifier as specifically illustrated in the drawings. For example, amplifier 10 of FIGURE 1 may have one of its sidewalls, for example left sidewall 23, recessed to eliminate boundary layer effects whereby the only two stable states for amplifier 10 would correspond to the power stream being directed toward right output passage 39 and central output passage 37 respectively. Likewise boundary layer effects may be entirely dispensed with, as in the case of amplifier 50 of FIGURE 2, and the left and right output passages vented so that only variations of the power stream from its central position are monitored at output passage 77. Further, both amplifier 10 and amplifier 50 may have their central output passages 37 and 77, respectively, removed and only a single flow divider or flow splitter provided between the left and right output passages such that the centrally stable position of the power stream provides equal flow to the left and right output passages. Of course, variations of this two output passage device are conceivable in accordance with the present invention.

Still further, it is to be recognized that the two merging streams provided in accordance with the present invention need not be precisely parallel. More particularly, it is possible to produce an evacuated region between the two streams when they are arranged at some small angle relative to one another. Such streams would then be substantially parallel for purposes of the present invention.

The angle between the streams however should not be large enough to permit deflection of either stream due to momentum interchange; that is, the primary mechanism by which the two streams merge to form a single stream should be the mutual entrainment between the streams.

While I have described and illustrated one specific embodiment of my invention, it will be clear that variation of the details of construction which are specifically illustrated and described may be resorted to without departing from the spirit and scope of the invention.

What is claimed is:

1. A pure fluid amplifier having an interaction region, means for establishing a power stream of fluid directed across said interaction region, at least one output passage communicating with the downstream end of said interaction region for selectively receiving said power stream, and means for selectively deflecting said power stream in said interaction region relative to said output passage, said amplifier being characterized in that said means for establishing a power stream comprises means for issuing two substantially parallel fluid streams into the upstream end of said interaction region, said streams being located such as to define an evacuated region between said streams to cause said streams to be deflected toward one another and merge downstream of said evacuated region to form a single stable power stream.

2. A pure fluid amplifier according to claim 1 wherein said means for issuing comprises a pair of nozzles, each nozzle having an egress orifice communicating with the upstream end of said interaction region, said egress orifices being separated by a substantially blunt surface.

3. The combination according to claim 2 wherein said pair of nozzles are formed from a single nozzle having a throat with a flow divider disposed therein.

4. The pure fluid amplifier according to claim 1 wherein said amplifier is a tri-stable pure fluid device, said interaction region being defined by a pair of sidewalls which are sufliciently close to said single stable power stream to produce boundary layer elfects between said sidewalls and said power stream, said at least one output passage being disposed to receive said single stable power stream when undeflected, and further comprising two additional output passages disposed respectively to receive said single power stream when the latter is attached to respective ones of said sidewalls.

5. A pure fluid amplifier according to claim 4 wherein said means for issuing comprises a pair of nozzles, each nozzle having an egress orifice communicating with the upstream end of said interaction region, said egress orifices being separated by a substantially blunt surface.

6. The combination according to claim 5 wherein said pair of nozzles are formed from a single nozzle having a throat with a flow divider disposed therein.

7. The combination according to claim 6 wherein said flow divider has an apex at its upstream end and converges in a downstream direction.

8. The combination according to claim 6 wherein said pair of nozzles have equal cross-sectional areas.

9. The combination according to claim 1 wherein said pure fluid amplifier is a proportional amplifier in which said interaction region has sidewalls sufliciently displaced from said single stable power stream to prevent boundary layer effects from deflecting said single stable power stream toward said sidewalls, whereby said single stable power stream is stable only in its undeflected position.

10. The combination according to claim 9 wherein is further provided a second output passage, said at least one and said second output passages being disposed to provide a differential pressure output signal as a function of the deflection of said power stream.

11. The combination according to claim 1 wherein is further provided a second output passage, said at least one and said second output passages being disposed to provide a differential pressure output signal as a function of the deflection of said power stream.

12. A pure fluid amplifier having an interaction region with an upstream end and a downstream end, at least one outlet passage communicating with said interaction region at said downstream end, source means for issuing a pair of substantially parallel fluid streams into said interaction region at said upstream end, said fluid streams being sufficiently proximate one another to define a low pressure region therebetween from which both streams entrain fluid and toward which both streams are deflected sufficiently to merge into a single deflectable power stream, the proximity of said streams being sufliciently close to maintain said fluid streams so merged for any and all deflected positions of said power stream.

13. The pure fluid amplifier according to claim 12 wherein said source means comprises a pair of spaced nozzles arranged to issue said fluid streams into said upstream end, said nozzles being separated by a blunt sur face defining the upstream boundary of said low pressure region.

14. The pure fluid amplifier according to claim 13 wherein said interaction region includes opposite sidewalls which are sufficiently displaced from said power stream to prevent boundary layer eflects between said power stream and sidewalls from deflecting said power stream toward said sidewalls.

15. The pure fluid amplifier according to claim 13 wherein said interaction region includes at least one sidewall positioned sufficiently proximate said power stream to cause boundary layer effects between said power stream and at least one sidewall to enhance any deflection of said power stream toward said one sidewall.

References Cited UNITED STATES PATENTS 3,080,886 3/1963 Severson 13781.5 3,181,545 5/1965 Murphy 13781.5 3,366,131 1/1968 Swartz 137-81.5 3,413,994 12/1968 Sowers 137-815 3,416,487 12/1968 Greene -137 81.5X

M. CARY NELSON, Primary Examiner WILLIAM CLINE, Assistant Examiner

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