US 3761657 A
A sensing device for a switch activated by fluid flow through a pipe. The flowing fluid exerts a force on the device which in turn activates the switch. The device in its preferred form includes a paddle with symmetrically placed apertures which cover substantially the entire effective surface and to allow flow through the body of the paddle to prevent cavitation and turbulence in the fluid. Reduction or elimination of these flow disturbances extends the service life of the paddle and its connection to the flow switch.
Claims available in
Description (OCR text may contain errors)
United States Patent [191 Miller FLOW SWITCH VANE WITH APERTURES COVERING SUBSTANTIALLY THE ENTIRE SURFACE AREA TO MINIMIZE TURBULENCE  Inventor: Leonidas C. Miller, 1321 Sombrero Dr., Monterey Pk., Calif. 91754  Filed: Apr. 14, 1972  Appl. No.: 243,934
 11.8. CI. ZOO/81.9 R, 73/228, 340/239 R  Int. Cl. HOlh 35/40  Field of Search 200/8l.9 R, 81.9 M;
73/228; 116/117 R; 340/239 R, 239 F  References Cited UNITED STATES PATENTS 2,421,768 6/1947 Voliazzo et a1. ZOO/81.9 R X 3,387,489 6/1968 Young 340/239 R X 2,789,175 4/1957 Mahr ZOO/81.9 R 2,347,830 5/1944 Kiburz et a1. ZOO/81.9 R X 3,535,479 10/1970 Smyers Jr. et al 200/83 T FOREIGN PATENTS OR APPLICATIONS 53,637 7/1942 Netherlands 340/239 Sept. 25, 1973 OTHER PUBLICATIONS IBM Technical Disclosure; Vol. 12, No. 8, P. 1195; Flow Switch For Low-Volume Fluid Flow, by J. G. Boles; Jan., 1970 Primary Examiner-J-Ierman J. Hohauser Assistant Examiner-Robert A. Vanderhye Attorney-Charles G. Lyon et a1.
[5 7] ABSTRACT 5 Claims, 7 Drawing Figures BACKGROUND OF THE INVENTION Paddles and other similar devices have been in use for sensing flow in pipes for some time. The paddle is rigidly connected to a switch which is normally located outside and above the pipe. When flow occursin the pipe, a dynamic head develops against the paddle and thereby activates the switch.
To obtain an accurate indication of flow through a pipe using such a paddle, the paddle must be of lightweight construction, provide a substantial frontal area to the flow and extend into the fluid stream. The lightweight construction is required in order that the unit may have low inertia and thus be more responsive and require less force to swing the paddle. In most applications, the paddle should extend across the diameter of the pipe carrying the fluid stream to insure operation with the pipe, only partially full or experiencing an anomalous flow situation. Finally the paddle must be of sufficient frontal area to provide an operative force for the switch under anticipated low velocity flow conditions.
This standard configuration has proven sufficient under normal operating conditions. However, if the paddle is placed near an elbow, bend or pump, the flow takes on nonuniform characteristics and very high flow rates are produced in certain portions of the flow stream. This nonuniform flow has resulted in turbulence and cavitation around the flow switch paddle. The rapidly changing forces on the paddle have caused high loads and severe vibration of the paddle, resulting in erratic action, rapid switching and sometimes early fatigue and loss of the paddle into the system.
SUMMARY OF THE INVENTION The improved sensing device of this invention in its several configurations provides an increased surface area parallel to the direction of flow and a body which is pervious to the passage of fluid. The device acts to sense the flow using boththe dynamic head of the flow and the drag of the fluid passing an increased surface area parallel to the direction of flow. At the same time, the pervious nature of the paddle prevents cavitation and helps to normalize the paddle movement. As a result, the operating life of the unit near an elbow, bend or pump is greatly increased and is comparable to the standard paddle configuration in a region of uniform flow.
The pervious nature of the novel paddle may be realized by any one of a multitude of configurations. The most basic of the designs uses a standard paddle which has had an extensive pattern of holes extending through the paddle in the direction of flow. The holes are kept relatively small to insure a large amount of drag from the fluid passing therethrough. By covering, the entire surface of the paddle with holes, the possibility of flow about the paddle creating cavitation and extreme turbulence is greatly reduced. Other configurations including a rigid screen mesh or a brush supported by a thin rigid back also provide a high amount of drag and a uniform pervious nature.
In summary, a paddle type sensing device for a flow switch is here disclosed. The paddle is rigid, perforated, creates a great deal of drag on the passing fluid and is pervious to the flowing fluid. Several configurations employing these characteristics are available.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view, partly in section, showing a sensing paddle assembled with a flow switch, and constituting a preferred embodiment of this invention.
FIG. 2 is a transverse sectional'view taken along lines 2-2 of FIG. 1.
FIG. 3 is a cross sectional view of the paddle configuration of FIG. 2 taken along lines 13-13 of FIG. 2.
FIG. 4 :is a front view showing a modification.
FIG. 5 is a front view of a second modification.
FIG. SA is a fragmentary view of the device of FIG. 5, with the parts shown in a different position.
FIG. 6 is a front view of another modification.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning now to the drawings, specifically FIGS. 1, 2 and 3, the flow sensing means 10 is shown as a paddle formed from a sheet of metal. The exterior dimensions of the paddle conform to present practice. The paddle 10 is given a slight curvature as shown in FIG. 3 to increase its strength and rigidity for better withstanding the forces associated with the flowing fluid. Many small holes 12 extend through the paddle 10 so as to cover its forward surface. The holes 12 extend through parallel to the direction of the flow to create the pervious condition, required for the reduction of cavitation and turbulence. The possibility that partial vacuum may build up and flow separation may occur behind the paddle 10 is greatly reduced by the presence of the pattem of holes extending across the total operative area. All portions of the paddle which form an obstruction to flow are immediately adjacent to at least one of the holes 12. A small area of the flow sensing means 10 about its point of attachment to the flow switch arm remains imperforate. This gives added strength to the paddle 10 around the point of attachment to the remainder of the system.
The holes 12 are shown as being relatively small. The use of small rather than large holes 12 in the flow sensing means 10 is beneficial because a greater amount of drag is created. The substantial drag created by the fluid passing through the small holes 12 adds to the force created by the dynamic head on the flow sensing means 10 to create greater sensitivity of the overall system. It has been found that holes having a diameter of one-eighth inch anda diagonal distance between centers of three-sixteenth inch provide sufficient drag on the fluid and yet provide sufficient flow through the body to reduce cavitation and turbulence. Naturally, the density and speed of the fluid and the thickness of the flow sensing means may require selection of a different configuration.
The paddle 10 is held to the extended arm 14 of the switch 16 by two screws 18. A flat surface 20 is machined on the arm 14 to accommodate the end of the paddle 10. A pipe 22 is illustrated to show placement of the device. A portion of an elbow 24 is shown to emphasize that the maximum benefit from this pervious sensing device is realized in disturbed flow conditions. An access pipe 26 with a mounting flange 28 is provided for mounting of the unit. Sufficient room is provided in the access pipe 26 to provide for the maximum travel of the switch arm 14. The switch 16 is normally a mechanical action switch that closes or opens an electrical circuit.
FIG. 4 illustrates an alternate configuration for the flow sensing device. A rigid wire mesh or screen 30 is shown in place of the perforated metal sheet 10. The screen 30 provides sufficient area and resistance to flow required by the flow switch 16. The screen 30 is also pervious and will prevent the. build-up of vacuum and excessive turbulence behind the sensing device. A- solid metal sheet 32 is provided for the coupling of the flow sensing device to the lever 14. Holes 34 are positioned to accept screws 18.
FIGS. and 5A illustrate another configuration which uses a disk 40 which is centered in pipe 22. The pervious nature of this configuration may be altered by slightly realigning backup plate 42 so that holes 44 on plate 40 and holes 46 on plate 42 are partially misaligned. When very light flow is anticipated, the holes 44 may be blocked completely. Switch arm 48 extends past the center line of disks 40 and 42 and is adjacent to plate 42 on the downstream side. A central machine screw 50 supports plates 40 and 42 and permits angular adjustment between them.
FIG. 6 shows yet another configuration of the paddle. Bristles 36 are positioned in a plane perpendicular to the direction of flow and are held in place by a conventional twisted wire backing 38. The bristles 36 mustbe of sufficient strength to remain relatively perpendicular to the direction of flow for sufficient drag. Again the bristles are pervious to the passage of fluid which inhibits the formation of a partial vacuum or extreme turbulence on the downstream side of the flow sensing device 10. A threaded coupling 39 is provided to connect the bristle paddle to the flow switch.
Having fully described my invention, it is to be understood that I am not to be limited to the details herein set forth but that my invention is of the full scope of the appended claims.
1. A flow switch having a means for sensing flow in a pipe, wherein said sensing means is pervious to fluids, said pervious sensing means comprising a brush having bristles and a thin rigid base.
2. A flow switch device for sensing flow in a pipe, said device having a sensor member extending into the path of the flow to be sensed, said sensor member having symmetrically placed apertures which cover substantially the entire effective surface of said member in order to minimize turbulence.
3. The device of claim 2 in which the sensor member comprises a rigid screen.
4. The device of claim 2 wherein the sensor member is curved transversely to enhance structural rigidity.
5. The device of claim 2 wherein the sensor member comprises a plurality of apertured plates, one of the plates being movable relative to another of the plates to vary the degree of alignment of the apertures in the plates.