US 3163229 A
Description (OCR text may contain errors)
Dec. 29, 1964 c. A. SALISBURY 3,163,229
PLASTIC SCREEN FOR WATER wm. FooT VALVES Filed June 25, 1962 TUE-4 @L 'Arroz His United States Patent O 3,163,229 PLASTIC SCREEN FR WATER WELL FOOT VALVES Clifford A. Salisbury, Box '716, Tonlrawa, Okla. Filed June 25, 1962, Ser. No. 204,782 6 Claims. (Cl. M6-234) The present invention relates to Huid strainers and more particularly, but not by way of limitation, relates to an improved screen for the foot valve located on the end of a tubing string in a water or other fluid well.
As is well known in the art, after a water well is drilled from the surface into a water bearing stratum, the upperV strata are sealed off by a string of pipe known as the casing. The lower end of the well bore adjacent the water bearing sands is usually left open or the casing is provided with large perforations to permit the water to seep into the casing or well bore, as the case may be. In any event, relatively large foreign particles such as chips of shale from the subsurface formation, rocks, leaves and other trash from the surface frequently find their way to the bottom of the well bore. When a second string of smaller diameter pipe, known as the tubing string, is lowered through the casing string to the water standing in the lower portion of the well bore, in order to withdraw the water, these foreign particles may enter the tubing string and clog the pumping mechanism unless a suitable Screening device covers the lower end of the conduit.
Screens heretofore provided in the art for the lower end of the tubing string have been fabricated of a metal, such as brass, and usually have been attached to the conventional foot valve or check valve provided at the lower end Vof the tubing string for maintaining the tubing string full of water so that a pump located at the surface will be primed and ready for instant production. These screening devices have in most cases been made integral with the foot valve and perform the added functionof protecting the downwardly projecting valve body guide stem of the foot valve. In any event, the metallic screens, even though fabricated from brass, are subject to relatively rapid corrosion in many localities. The rigid metallic screens quite frequently are bunged-up as the tubing is lowered through the casing. Further, should the tubing string inadvertently be dropped or otherwise lowered so far as to contact the bottom of the well bore, the screen will usually be damaged to such an extent that the valve guide stem of the foot valve associated with Vthe screen will be bent and prevent operation of the foot valve. In more recent times, the now common use of plastic hose for tubing has created a situation in which virtually none of the brass screens ever reach the bottom of the well bore without suffering damage. This is due to the fact that the plastic tubing is wound on a spool for storage and transport. 'When the tubing is unwound from the spool, the plastic tubing will invariably have a kink or sharp curvature at the lowerV end which will direct the lower end of the rigid metallic screen against the wall of the casing as the tubing is lowered into the well. The lower end of the screen then strikes each gap formed between the adjacent ends of each two joints of casing and is jammed, bent and quite frequently torn from the foot valve which it is designed to protect.
Therefore, it is a primary object of the present invention to provide a highly flexible screen for connection to the foot valve or lower end of the tubing string which is virtually indestructible under normal usage and will withstand forces applied either laterally or axially along the screen. The novel screen structure comprises, in general, a cup shaped body of resilient plastic material having an annular rim portion at the upper end for connection around the end of a foot valve, a plurality of generally ICC longitudinally extending ribs connected to the rim portion and extending downwardly, and a capvportion connected to the lower end of the ribs.
Another very important object of the present invention is to provide a screen of the type described which is highly resistant to corrosion encountered in water wells and the like.
Yet another object of the present invention is to provide a screen of the type described which has virtually no resistance to fluid flow therethrough and which thereby permits high efficiency of a suction type water pump located at a surface.
Still another object of this invention is to provide a screen of the type described and a foot valve, orother conduit, such that the screen may be connected very quickly and easily to the foot valve and remain attached even when subjected to severe forces tending to tear the screen from the foot valve.
Many additional objects and advantages of the present invention will be evident to those skilled in the art from the following detailed description and drawings, wherein:
FIG. 1 is a side elevation, partially in section, of a screen constructed in accordance with the present invention, the screen being shown in combination with a foot valve for a water well which has been modified in accordance with the present invention;
FIG. 2 is an enlarged view of a portion of the cutaway View of FIG. l and better illustrates the details of construction of the screen and the foot valve to which the screen is attached;
FIG. 3 is a vertical sectional view of a string of casing showing the improved screen in operative position on the lower end of a plastic tubing string as the tubing string is lowered into a string of casing; and,
FIG. 4 is a vertical sectional view of the lower end of a well bore showing the novel screen attached tothe lower end of a metallic tubing string with the weight of the tubing string resting on the screen which is inY contact with the bottom of the well bore.
Referring now to the drawings, and more particularly to FIG. 1, a screen constructed in accordance with the present invention is indicated generally by the reference numeral 10. The screen 10 comprises a generally cup shaped body of resilient plastic material having an annular rim portion 12, a plurality of ribs 14, and a cap portion 16. The entire cup shaped body may be molded as a single unit from any tough, resilient plastic material which has appropriate corrosion resistant properties in the pal'- ticular fluid in which the screen is to be immersed and operated. However it is within the purview of this invention to utilize polyethylene which has been found to be especially suitable for molding the screen 10.
The screen l0 is illustrated in combination with the tubular body 18 of a foot valve assembly which may be attached to the lower end of the tubing string of a Water well, as hereafter described in greater detail. The'foot valve should be of the type having no parts projecting below the lower end of the body 18, such as the foot valve described in my copending application Serial No. 204,783 entitled Check Valve, tiled on luneY 25, 1962. The lower end 20 of the valve body 18 has a cylindrical outer lower surface 22 in which an annular groove 24 is machined. The annular groove 24 preferably has a rectangular cross section, as best seen in FIG. 2, so that the lower shoulder 26, in particular, as well as the upper shoulder 27 will lie in a plane substantially perpendicular to the axis of the tubular body 18. The rim portion 12 of the screen 10 is sized to lit snugly around the cylindrical outer surface 22 of the valve body 18 and is provided with an annular, inwardly projecting shoulder 28 which extends, into the annular groove 24. The inwardly pro- Patented Dec. 29, i964` p r Y a Y jecting shoulder 28 may be rounded to provide a cross section, substantially as shown in FIG. 2, to increase the ease with which the screen may be telescoped over theV end ofthe foot valve. Even so, when the rounded annular shoulder 28 is insertedrin the square annular groove 24, the rim 12 will function as a stout, resilient vband tending to hold the shoulder 28 in place. Since the lower shoulder 26 of the groove 24 is perpendicular to the axis of the body 1S, the screen 10 cannot be pulled from the end of the body 18 because no inclined surface is present to'exert a wedging force to expand the rim 12 and permit the shoulder 28 to leave the groove 24. For the Ysame reasons, the rim portion 12 cannot be forced further onto the cylindrical surface 22 because ofthe square upper shoulder 27 of the annular groove 24.
' The ribs 14 are, preferably, approximately the same width as they are thick so as to have a generally square cross section. 'Ihis permits the ribs to flex in' all direc tions with approximately equal ease andtends to maintain the ribs equally spaced regardless of the direction from which a distorting'force is applied to the screen.
cally =replaced and are considered expendable afterV one` use.
Referring now to FIG. 3, the screen 10 is shown attachedto the foot valve body 18 which in turn is connected to the lower end of a flexible plastic hose 4t), as-
previously mentioned, which is frequently used as the tubing string in shallow water wells. Two joints 42 and 44 of Va casing string disposed in a well bore are interconnected by a conventional threaded collar 46, resulting inan annular gap 48 between the ends of the two joints of pipe 42 and 44. The plastic hose 4G is shown as having a curl or kink at the lower end thereof as a result of storage on a conventional spool. As the plastic hose 40 is unreeled from the spool and lowered through the casing, the foot valve body 18 and in particular the screen 10 connected thereto will be directed against one wall of the casing. The lower end of the screen 1t) will thereby Also, the longitudinally extending spaces 3l) formed be- Y tween each adjacent pair of ribs V14 are preferably of ap-v proximately the same width as each of the ribs 14.V In order for the arca of the fluid passageway throughV the screen to be equal to the area of the passageway through the tubular body 1S, the ribs should then be at least as long as the radius of the iiuid'passageway. However, in order to provide the desired degree of liexibility, the ribs 14 are preferably made approximately as long as the diame'ter of the rim portion 12. This will normally be approximately three timesl as-great as the inside diameter of the tubing string so that the total cross sectional area of fluid passageways through the screen 10 will be atleast twice as great as the cross sectional area of the .fluid passageways through the tubing, and in most cases be tween three and four times as great, so as to oler very little comparative resistance to fluid liow and a corresponding low pressure drop `across the screen.
The cap portion 16 is preferably provided with a convex lower surface 32. In order to increase the flexibility of the cap portion and reduce the quantity of plastic material used, the Vcap portion 16 may be concavo-convex, substantially as shown in FIG.,1, and have a constant thickness preferably corresponding to the thickness of the ribs 14 and the'rim portion 12.V The cap portion 16, as mentioned, is connected to the lower endV of the ribs 14, and maintains the Vribs in spaced,rsubstantially parallel re-Y lationship, However, the cap portion 16 preferably has a slightly smaller diameter than the rim portion 12 so that the entire screen 10-has a slight downward taper. Thus it will be noted that any two ribs 14 ytaken in conibination with the interconnecting portions of the rim portion 12 and the capvportion 16 will approximate a parallelogram which contributes substantially to the flexibility and functionality of the/screen as hereafter described in greater detail.
In operation the screen 10 is connected to the lowerr end of the tubing string, such'as tothe body of the footV valve 18, merely by slipping the rim portion 12 over the lower end 20 of the body 18. Even though the rim portion 12 may be of slightly less diameter than the lower .end 20, the resilient plastic material from which the screen 10 is molded will expand su'iciently for'the rounded shoulder 23 to slipj over the end 20 and still provide a tight fit around the cylindrical surface 22. when the annular shoulder 28fseats in the annularV groove-24. Once the annular shoulder 28 is in position in the annular groove 24, the square lower and upper shoulders 26 and 27 will prevent the annular shoulder 28 and the rim portion 12 from sliding longitudinally along the end 20 of the foot valve body 18 as previously described. Thus the be deformed substantially as illustrated inFlG. 3 due to contact of the cap portion 16 with the wall of the joints screen 10 cannot be pulled from the foot valve body 18 or will not be jammed upwardly until a knife blade or the like is inserted under the rim portion 12 and the an- 42 and 44. The screen 10 is readily deformable in the manner illustrated because of the flexibility of fthe plastic material from which' the screen is molded and because of the fact that the ribs 14 in conjunction with the rim portion 12 andthe cap portion 16 form a number of parallelograms as previously described, which, as it is well known, are stable geometric figures. However, since the ends of the ribs 14 are rigidly connected to the rim portion 12 and to the cap portion 16, ythe ribs 14 will actually assume a slight S-shaped configuration substantially as illustrated in FIG. 3. It will be noted that the plane of the upper edge of the cap portion 16 remains substantiallyV parallel to the plane of the rim portion 12 such that a line tangent to the convex curvature 32 of the cap portion 16 is vertical and coincides with the wall of the casing pipe. Therefore the rounded cap portion 16 of the screen 10 will easily slide past the gap 48 without dangerof damaging the screen. Even though the screen 10 will probably be pressed against the side of the casing after it reaches the lower part of the well, untilthe weight of the foot valve body 18 straightens the plastic hose 40, and the area of the elongated slots 30 is somewhat reduced'by the distortion, the total area of the openings will still be substantially greater than the cross sectional area of the hose 40 and fluid will still easily pass through the screen 10 with very little pressure drop. 1
FIG. 4 illustrates how the screen 10 collapses when a metal tubingl string is inadvertently dropped against the bottom of awell bore 50 to prevent destruction. In FIG. 4 the foot valve body 18 to which the screen 10 is connected is illustrated as threaded onto the lower end of conventional metal tubing pipe 52 which of course has a substantial weight. In the event the tubing 52 is inadvertently dropped or otherwise bumped against the bottom of the well bore 50, thescreen 10 will assume'the position indicated. The convex'curvature 32 of the cap portion 16 will readily permit the cap portion 16 to rotate or spin about the vertically disposed longitudinal axis as it contacts the bottom 50 of the well bore so that the ribs 14 become twisted in an S-shaped configuration until the en-Y tire cup shaped' screen V10 is collapsed. If the external diameter of the cap portion 16 is slightly smaller than the internal diameter of the rim portion 12, the ribs 14 and the cap portion-16 may be forced partially into the interior of the foot valve body 18 such Vthat the likelihood of cut'- ting the ribs 14 will usually be reduced. However, the cap portion'16 should not be made appreciably less than the diameter of the passageway throughithe foot valve A will resume its original shape after a very short period of time.
In the event the screen 1? should become clogged with material such as leaves or paper, suction acting on the clogging material may tend to collapse the ribs 14 inwardly so long as suction is maintained by a surface pump. However, as soon as the pump is stopped to equalize the pressure, the resilient ribs 14 will spring back to their original positions and tend to dislodge the leaves or other clogging material which might otherwise cling to and permanently clog a conventional rigid screen. Therefore, the screen is to a very large degree self cleaning.
It will be obvious to those skilled in the art that the screen 10 can be very economically molded as an integral unit in a conventional single step injection mold process so as to produce an exceedingly economical screen. Further, the screen lll may be securely connected to a suitable` foot valve body 18, or any other suitably adapted conduit, merely by telescoping the rim portion 12 over the grooved end of the tubular body 18. Experience has shown that the screen 10 will absorb compression from virtually any angle Without signiiicant harm and, in most cases, with no appreciable decrease in screening eciency. Further, even when compressed and distorted completely out of shape, in most instances the screening device will still provide total fluid passageways at least as great as the uid passageways of the tubular conduits to which Vthe device is attached.
Having thus described a preferred embodiment of the present invention, it is to be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invenftion as dened by the appended claims.
1. A screen for a foot valve having a tubular body with a uid passageway therethrough, the screen comprising a generally cup shaped, axially collapsible body of resilient plastic material having an 'annular rim portion sized to fit tightly over the end of the tubular body; a plurality of flexible ribs connected at one of the ends thereof to the rim portion, the unexed ribs extending in a generally parallel relationship and being spaced apart to form elongated slots between adjacent ribs, and a circular, convexly curved cap portion connected to the other of the ends of the ribs, the ribs being Vconnected to the periphery of the cap portion.
2. A screen for a foot valve having a tubular body with a Huid passageway therethrough as deined in claim l further characterized by an inwardly projecting annular shoulder within the rim portion for securing the rim portion on the tubular body. Y
3; A screen for a foot valve having a tubular body. with a iiuid passageway therethrough as defined in claim 1 wherein the ribs have substantially a square cross section.
4. A screen for a foot valve having a tubular body with a iluid passageway therethrough as defined in claim 1 wherein the length of the ribs is approximately equal to the diameter of the rim portion.
5. A screen for a foot valve having a tubular body with a iluid passageway therethrough as defined in claim 4 wherein the cap portion has a diameter less than thediameter of the rim portion.
6. A screen for a foot valve of the type having a tubular body with :a'uid passageway therethrough, said screen comprising an Vaxially collapsible, generally cup shaped body of resilient plastic material, said cup shaped body having anannular rim portion dimensioned to f rictionally surround said tubular body;
a plurality of exible, resilient elongated ribs of substantially square cross-section each connected at one of their ends to said rim portion in circumferentially `spaced rel-ation therearound, said ribs being spacedy vapart to form elongated slots between adjacent ribs;
and a circulan'convexly curved cap portion of smaller diameter than said annular rim portion connected at its periphery to the other ends of Vsaid ribs with said ribs Vbeing connected to said cap portion lin circumfereutially spaced relation around the periphery thereof.
References Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTS 724,368 8/42 Germany.
BENJAMIN HERSH, Primary Examiner.