US 2990017 A
Description (OCR text may contain errors)
June 27, 1961 J. P. POWERS 2,990,017
WELLPOINT Filed June 24, 1958 T11:1.1./ A Z H 40 JT; "WW U -n TU PM v INVENTOR (fOSEP/l PPoWz-PS ATTORN 52 United States Patent Ofiice 2,990,017. Patented June 27, 1961 2,990,017 WELLPOINT Joseph P. Powers, Boonton, N.J., assignor to Moretrench Corporation, Rockaway, NJ., a corporation of New Jersey Filed June 24, 1958, Ser. No. 744,210 (Ilaims. (Cl. 166157) This invention relates to wellpoints; and more particularly to improved screen cylinders for use in wellpoints.
A wellpoint is a pipe device which is inserted into the ground in order to dewater the soil about it. Such devices are normally used where an excavation is to be made and the water level of the soil is above the elevation of the bottom of the area to be excavated.
A wellpoint consists of a center pipe with a coupling at its upper end to which a riser pipe is attached. A jetting tip is fitted to the bottom end of the center pipe and an open mesh screen cylinder which surrounds the center pipe, is positioned between the coupling and the jetting tip.
A wellpoint is sunk into the ground by connecting the riser to a pressurized source of water. A stream of water is forced through the riser pipe and into the wellpoint. In a wellpoint of typical construction, the water then flows into the center pipe, through a ball valve and then out through the jetting tip in the form of a jet stream. As the water leaves the jetting tip it erodes the soil about it, thus providing a hole beneath the wellpoint into which the device sinks. This is continued until the desired depth is reached, 'at which point the supply of jetting water is shut oii.
The riser pipe is then connected to a header pipe which in turn is connected to a suction pump and a suction is set up within the wellpoint. A combination of the ball valves buoyancy and the suction causes the ball valve to close the passageway through the jetting tip. With the jetting tip closed, the suction pulls the water which is in the soil surrounding the wellpoint through the screen cylinder, into the center pipe, and into the riser and header from which it is discharged.
The purpose of the screen cylinder is to furnish a large open area for the water in the soil surrounding the wellpoint to flow through. This screen also acts as a filter and prevents particles of soil from being drawn through the wellpoint during the dewatering operations. Prior to the present invention various types of screen cylinder construction were used. Some of these screens were so fragile that special external protection, such as a cage of bars, was necessary to protect them. Other screens required a layer of strong and coarse mesh or a perforated metal sheet to be wrapped around the fine mesh of the screen cylinder in order to protect it. These prior devices have suffered from many shortcomings, not the least of which was that the effective open area through the screen cylinder was generally the equivalent of only a small percentage of the actual surface area of the screen cylinder.
Accordingly, it is an object of the present invention to provide a strong and yet eflicient screen cylinder for wellpoints. It is another object to provide such a screen cylinder which does not require the use of any external protection, so that it has full unobstructed contact with the surrounding soil. It is a further object to provide a screen cylinder which is not only strong and unobstructed but one which also has a large effective open area therethrough. It is still another object to provide a screen cylinder which is woven of warp and fill Wires so that the fill wires extend axially of the wellpoint, permitting the wellpoint to be inserted into the ground with a minimum of friction between the screen cylinder and the soil, and a minimum hazard of damage to the screen.
In the specification and the accompanying drawings a preferred embodiment of the present invention in wellpoints is shown and described. It is to be understood that this is not intended to be exhaustive nor a limiting of the invention, but on the contrary, is given for the purposes of illustration in order that others skilled in the art may fully understand the invention, its principles and the manner of carrying it out.
In the drawings:
FIGURE 1 is an elevational view of a wellpoint;
FIGURE 2 is a fragmentary view of the wellpoint partially in vertical section along the line 2-2 of FIGURE 1;
FIGURE 3 is a plan view of a flattened portion of the internal support cylinder for the woven wire screen cylinder FIGURE 4 is a fragmentary plan view of a portion of the screen cylinder showing the type of weave used;
FIGURE 5- is a sectional view of the screen cylinder of FIGURE 4 taken along the line 55 of FIGURE 4;
FIGURE 6 is a sectional view of the screen cylinder of FIGURE 4 taken along the line P6 of FIGURE 4; and
FIGURE 7 is a perspective view showing the intersection of two fill Wires and one warp wire with the elfective area of one of the openings through the scren indicated by shading.
Referring to FIGURE 1, a complete wellpoint 10 is shown which is connected to a riser pipe 12. The components of this wellpoint 10 are the jetting tip 14, the screen cylinder 16, and the upper coupling 18, and as shown in FIGURE 2, a center pipe 20, a screen supporting cylinder 22, a ball valve assembly 24 and a ring valve 26.
The ball valve assembly 24 shown in FIGURE 2 comprises a ball valve 28, a support basket 30, and a valve seat 32. The support basket 30 has a series of arms 34 which help to hold the valve seat 32 in position by spring action. The operation and advantages of basket 30 are described in more detail in the copending application of the present inventor, Serial No. 720,287, filed March 10, 1958.
The ball valve 28 has a wooden center which gives it buoyancy in Water while assuring a true spherical shape. If desired, this ball valve 28 may be covered with an elastic coating which protects the ball from wear and tear and helps to achieve a close fit between ball valve 28 and the valve seat 32.
The valve seat 32 is a flat disc which abuts a cylindrical shoulder ring 36. This valve seat 32 has a central opening 38 therein which is of a smaller diameter than the diameter of the ball valve 28. When suction is applied to the center pipe 20 the ball valve 28 is pulled into this opening 38, thus closing olf the lower portion of the jetting tip 14 from the center pipe 20. When jetting water is forced through the center pipe 20, the ball valve 28 rests in the support basket 30, which prevents the ball valve from being pulled through the jetting tip with a stream of jetting water. The shoulder ring 36 is set against the lower portions of a series of vertical ribs 42 which are attached to and longitudinally spaced about the center pipe 20 and which are also attached to the upper inner portion of the jetting tip 14.
When jetting water is being pumped through the center pipe 20 and out the jetting tip 14, it is desirable to have most of this water flow through the jetting tip 14; to accomplish this, a flat ring valve 26 is provided on top of the valve seat 32. As jetting water passes through the opening 38 in the valve seat 32, a slight turbulence or backwash is created in that area since the diameter of opening 38 is slightly less than the inside diameter of center pipe 20. This turbulence and backwash lift up the ring valve 26 and hold it against the bottom of the spacer ribs 42, thus almost completely sealing off the annular is 3 space between the outer wall of the center pipe 20 and the inner wall of the cylindrical shoulder ring 36. Therefore, most of the jetting water is confined within the jetting tip 14 and forced out of the tip in'the form of a jet stream. However, due to the loose fit of the ring valve 26 Within the shoulder ring 36, a small volume of the jetting water fiows upwardly between the ribs 42 and out through the screen cylinder 16. This slight backwash has a beneficial effect in that it helps to keep the screen 16 clear while sinking thewellpoint into the ground.
When the well point is sunk to the proper elevation, the jetting water is turned 011 and the ring valve 26 drops back onto the valve seat 32. Water in the soil causes the ball valve 28 to float upwardly against the valve seat 32 and close the opening 38 therein. When suction is applied, the ball valve 28 is sucked even more tightly against the valve seat 32. This suction causes water in the soil surrounding the wellpoint 10 to be pulled through this screen cylinder 16, through the perforated supporting cylinder 22, between the ribs 42 and into the center pipe 20. From there it passes into the riser pipe 12 and then into a header from which it is dicharged.
To strengthen the screen 16 during the wellpoint pumping operations (that is when water is being withdrawn from the soil surrounding the welpoint) and also to Withstand abuse during handling and installation, a perforated support cylinder 22, as shown in greater detail in FIGURES 2 and 3, has a series of elongated slots 40 therein which are so positioned that they do not interfere with the passage of Water through the cylinder screen 16 and the flow into the center pipe 20.
The eifectiveness of a Well point is determined by the amount of water which may be efficiently withdrawn from the soil surrounding the device. This efliciency of operation is dependent upon the amount of effective open area in the screen cylinder 16.
As shown in FIGURES 4, 5 and 6 in particular, the screen cylinder 16 in the present invention is comprised of a Weave of warp wires 44 and fill wires 46 which have carefully selected diameters. The relationship of these wires is such that the diameter of the warp wires 44 is substantially greater than the diameter of the fill wires 46. In an actual embodiment of the present invention it was found that warp wires with a diameter of about .028 inch and fill wires with a diameter of about .016 inch when Woven together provided a screen cylinder which gives excellent results. The diameter of the warp wires is thus approximately 75% greater than the diameter of the fill wires. In the particular weave illustrated, which is known in the trade as a plain Dutch weave or corduroy weave, the fill wires 46 pass over one warp wire 44, under the next succeeding warp wire, then over the following warp wire, and so on. The adjacent fill wires 46 at either side of their neighboring fill wires extend on the opposite sides of each of these warp wires.
It has been found that improved soil penetration is obtained with a screen cylinder having the above described weave when the fill Wires 46 are run in a direction which is substantially parallel to the vertical axis of the wellpoint. With the fill wires so oriented the screen cylinder 16 meets less resistance from the soil about it when the wellpoint is sunk into the ground. This ease of penetration is due to the fact that the fill wires 46 are outermost on the screen cylinder 16 and aligned in the direction in which the wellpoint 10 is being sunk. Therefore, less resistance is encountered than is the case when the fill wires are aligned circumferentially about the wellpoint, and there is less hazard of damage to the wires.
wires and sixty-eight fill wires are provided in each square inch of screen area (a 12 x 68 mesh). With this weave the effective open area through the screen is almost 50% of the total surface area of the screen. This will be demonstrated below. 7
Heretofore, the screening materials commonly used in the wellpoint industry have been flat rectangular meshes, 40 x wires, to the inch, .010 inch diameter, or x wires to the inch, .010 inch diameter. These rectangular meshes have open areas in the range of 25 to 35 percent of the total surface area of the screen.
Until the present invention, a Dutch weave screening material has not been used in the wellpoint industry. Dutch weave screening is used in filtration systems in the various process industries, but the type of Dutch weave used therein is fundamentally diiferent from the weave of the present invention. In the conventional Dutch weave used in the process industries, the warp wire has a .023 inch diameter and the fill wire has a .0165 inch diameter. In such a weave, the minimum size opening, in other words the point at which a filtered particle is retained, is shown by the shaded area 50 in FIGURE 7. However, in the weave of the present invention, the warp wire has a .028 inch diameter (which is larger than heretofore) while the fill wire has .0165 inch diameter (the same as the conventional process industry weave.) In this weave the shaded area 50 (shown in FIGURE 7) is enlarged, so that it is no longer the minimum size. As a result of this enlarging of area 50 the controlling minimum size opening as shown in FIGURES 4 and 5 is the shaded area indicated at 51, which is between alternate fill wires 46.
In the weaving of tight meshes it is the practice to crush the filled wires together to a very slight degree so that the actual diameter of the wires at the point of crushing is slightly reduced. As a result of this crushing effect a mesh of .028 inch warp wires and .016 inch having 68 strands of the .016 inch Wire may be provided in one inch. This is accomplished in the mesh weaving process wherein the .028 inch warp wires are first set up in loom, and then the shuttle draws the .016 inch fill wires back and forth to complete the woven mesh. In order to achieve a tight sturdy uniform mesh, the shuttle tension is adjusted to draw each fill wire tightly against its adjoining fill wire during the weaving process. This tight adjustment results in a slight crushing of the fill wires at the points of contact between the adjacent fill wires. As a result of this slight crushing 68 wires of .016 inch diameter may be woven into a total space of one inch. Because of the slight crushing of the fill wires the additional .088 inch of length over one inch, which would be expected with the 68 wires of .016 inch diameter, is reduced by the crushing. Thus, a tightly woven and exceptionally strong weave is obtained.
However, the direction of the fill wires relative to the 7 By shifting the minimum size opening to the area 51, the effective open area of the Dutch weave is increased to almost fifty percent, at the critical point Where filtered particles are retained. This is of particular advantage in the wellpointi ndustry, as'will be shown by a comparison of wellpoint operation with conventional filtration.
The water removal and pumping operation of a wellpoint is considerably difierent from the operation of a normal chemical filter. Generally a chemical filter acts to pass the filtrate while retaining all particles above a given size. Gradually the open area of the filter screen becomes blocked with retained particles and, thus, the pressure drop across the filter screen exceeds a reasonable value. When this occurs the filter must be shut donw and backwashed to clear it of the retained particles which create the blockage. However, the action of a wellpoint is quite different. As soon as a wellpoint is installed and the removal of water by pumping is begun, soil particles collect at the surface of thescreen 16, eifectively blocking much of the screens open area. The only entrance for the water is through that portion of the screen opening that is not obstructed by soil particles. Thus, the wellpoint screen, unlike a conventional filter screen, is always partially obstructed by particles, instead of operating on a cycle. The wellpoint screen cannot be effectively backwashed to clear it of the collected particles inasmuch as the particles would remain adjacent to the screen and return thereto as soon as the pumping operations were started again. Therefore, a wellpoint screen must be provided which will retain soil particles and, yet, provide a sufiicient open area therethrough so that enough water may be withdrawn from the surrounding soil to make the wellpoint pumping operation efiicient and practical. A mesh screen in accordance with the present invention permits this to be accomplished more efficiently than with any mesh heretofore devised.
By shifting the minimum size opening from the area 50 of FIGURE 7 to the area 51 of FIGURES 4 and 5, the open area of the mesh at the critical point, that is, where particles are retained, is increased to almost 50 percent. In a mesh in accordance with the present invention, a particle passing area 51, will also pass through area 50 and entirely through the mesh screen 16, and up the center tube 20 to be discharged. Thus, the intricate and restricted internal passages through the mesh screen 16 are kept free of obstructing sand particles. Instead these obstructing sand particles are retained at the shaded area 51, where because of the large, effective open area, which is about 50 percent of the total surface area, the restriction of water flowing through the screen 16 is held to a minimum.
The inherent advantages of a preferred mesh of the present invention were demonstrated in laboratory tests. This mesh, in contact with any soil of given grain size and degree of compaction, yielded more water per square inch of screen, per inch of applied vacuum, than the 40 x 45 rectangular mesh tested.
It would be expected that enlarging the minimum size opening of the mesh as described above would enable soil particles of larger size to pass through the mesh. In dry sieving such, is the case. However, in well point pumping the reverse is true.
In an actual laboratory test, it was found that a 12 x 68 mesh weave in accordance with the present invention passed less weight of any given soil than the old type 40 x 45 mesh passed, although the effective dry particle opening through the new 12 x 68 mesh is about 0.42 mm., as compared with an opening of about 0.31 mm. for 40 x 45 mesh. The reasons for the improved filtering operation of the enlarged openings is not fully understood. It is believed that there is a buildup of larger size soil particles around the 1-2 x 68 weave of the present invention than there is with the 40 x 45 weave and that this buildup of larger particles holds back some of the material that the 40 x 45 mesh passes.
From the foregoing description it will appreciated that the present invention provides a practical wellpoint cylinder screen which insures improved dewatering and increased efiiciency. It will thus be appreciated that the present invention accomplishes the aforementioned and other advantageous objects. However, it should also be emphasized that the foregoing description of the particular embodiment of the present invention which is shown in the accompanying drawings is intended to be merely illustrative of the invention and not restrictive of the scope of the invention which is defined in the following claims:
1. In a wellpoint a single layer of perforated screen of the type described comprised of a tight Dutch weave of warp and fill wires, adjacent fill wires crossing by each other and being in tight contact with each other at the point where they cross, said screen having a series of interior openings therein of greater size than a series of respective openings on the surface of said screen which communicate with said interior openings whereby material passed through said surface openings will pass through said interior openings maintaining said interior openings free of obstruction.
2. In a wellpoint a single layer of perforated screen of the type described comprised of a tight Dutch weave of warp and fill wires as defined in claim 1 wherein said fill wires are directed substantially parallel to the longitudinal axis of the wellpoint.
3. A wellpoint screen cylinder comprised of a tight weave of warp and fill wires wherein the diameter of each of the warp wires is approximately .028 inch and the diameter of each of the fill wires is approximately .016 inch, the tight weave having approximately twelve warp wires and sixty-eight fill wires to each square inch of woven surface, said fill wires being positioned in close fitting contact with each adjacent fill wire being slightly crushed at the point of contact with the adjoining fill wires whereby sixty-eight fill wires are compacted into each inch of width of screen transverse to the direction of the fill wires.
4. A wellpoint screen cylinder comprised of a tight weave of warp and fill wires as defined in claim 3 wherein said fill wires are directed substantially parallel to the longitudinal axis of the wellpoint.
5. In a wellpoint a perforated single layer of screen of the type described comprised of a tight Dutch weave of warp and fill wires, adjacent fill wires crossing by each other and being in tight contact with each other at the point where they cross, said screen having a series of interior openings therein of greater size than a series of respective openings on the surface of said screen and which communicate with said interior openings whereby material passed through said surface openings will pass through said interior openings maintaining said interior openings free of obstruction, said warp and fill wires having diameters in the ratio .of about 7:4 respectively.
References Cited in the file of this patent UNITED STATES PATENTS 208,619 Ludlow Oct. 1, 1878 2,088,499 Specht July 27, 1937 2,148,001 Vultorius Feb. 21, 1939 2,858,894 Akeyson Nov. 4, 1958