US1591511A - Well tool - Google Patents

Description

0. A. CAVINS WELL TOOL Y Filed March 10, 1925 :5 Sheets-Sheet 1 Hal/1 V ZKQZIZZVENTOR .OMAR-A.CAVINS..

BY 6 g m k ATTORNEYS.

a July 6 1926. 1,591,511 o. A. cAvlNs WELL TOOL Filed March 10, 1925 3 Sheets-Sheet 2 FIG. 3

INVENTOR. OMAR F\.CAv|Ns.

Ax- W Q ATTORNEYS.

July 6 1926.

Q. A. CAVINS WELL TOOL Filed March 10,- 1925 3 Sheets-Sheet 5 TT II'\\ l- INVENTOR ARH HVIN x, 1

ATTORNEYS H M K 0 M 60mm 4 J Mm Patented July 6, 1926.

UNITED STATES PATENT OFFICE,

0mm A. oavms, or LABEDO, TEXAS.

WELL TOOL.

Application filed um]; 10, 1925. Serial No. 14,415.

spect, my method and the bailer form a.

radical departure from the ordinary manner of operation and the ordinary bailers. These are generally of the ordinary gravity filling type, bailers with a special shoe or base, to agitate the compacted material by dropping or spudding the bailer into the sand or other material in the bore hole.

'Another type is known as pump bailers.

In drilling deep wells, such as oil wells.-

' met with in which they are absolutely useless. In such extremity, drilling tools must be rigged up and used to loosen the compacted material, so that it may be handled by the known bailers. In the present procedure of cleaning out producing wells, the casing is frequently injured so as to permanently damage the well andrequire re-drill- 111 Ily my improved method'and the bailer, I can take u material, witliout previous agitation. This is due "to the utilization of the difl'erence of pressure inside my bailing apparatus and the outside pressure due to the depth of the well, and the head of oil and sand contained in the well. This difference of pressure Icause to function to force the sand or other consolidated material into' a bailer chamber at the base of the bailer, and it may then be removed by withdrawing the bailer.

My method and bailer may be broadly described as follows:

A long bailer tube has several compartments comprising a pressure tank which is filled with air at the surface of, the well, preferably at atmospheric pressure, an oil chamber ispositioned below the pressure tank and connected thereto b a series of valves, and below this oil cham er is a bailer valve.

compacted sand and similar or load compartment, which communicates with the bottom of the bailer by a special A separating piston divides the oil chamber from the load compartment, and when the appliance, after being lowered in the well, strikes the sand, the series of valves between the oil chamber and the compression tank are opened so that the excess of pressure outside the bailer forces the oil into the compression tank, causes the separating piston to rise and the sand to be forced through the special valve, into the load compartment. 1

A number of specific features which are embodied in my bailer include the followmg:

A system of valves by which the high air pressure in the pressure tank is used to aid the clearing of the load chamber at the top of the well, if this is necessary. I also include a safety valve to allow the air to escape at certain designated pressures. The system of valves connectingv the oil chamber .and the pressure tank are'caused to operate by the bailer striking the compacted material and in connection therewith I have a control dash-pot of a novel type. This dashpot is arranged to operate at a certain rate so as to control the opening of the main valve between the oil chamber and the air tank to allow the flow of oil through such valve in accordance with the mathematical. formula of the flow of'fluids through orifices under varying hydrostatic heads.

A novel valve is employed at the base of the load compartment which may be bodily dropped to allow discharge of the load. For use in wells having a crushed or crooked casing with a passage too small for the bailer, a. small bore bailer tube" may be attached in the lace of the valve. I also employ a new eature in a pressure equalizing valve in the wall ofthe oil chamber to communicate between the load com artment and the well after the separating piston has risen above this equalizing valve. A number of novel features beyond those above mentioned will .be apparent from the descri tion and claims.

l\ y invention will be more clearly understood as to method and improved bailer from the follo'win description, taken in con-' nection with the awings, in.which:--

Figure 1 is a vertical section of the upper portion of my bailer, showing the part containing the air tank, the main valve system, the control dashpot and part of the oil chamber.

Figure 1 is a vertical section of the lower part of the bailer, this part being connected immediately below that shown in Figure 1.

This figure illustrates part of the oil chamber, the load compartment, the separating piston therebetween, the pressure equalizing valve and the special discharge valve atthe bottom of the load compartment. v

Figure 2 is a vertical section at right angles to Figure 1 showing the details of the slide valve assembly and part of the main valve system. This is a section on the line 22 of Figure 4 in the direction of the arrow.

Figure 3 is a partial section similar to Figure 1 with the slide valve lowered and the dashpot piston in its lowest position.

Figure 4 is a horizontal section of Figure 1 on the line 4-4 in the direction of the arrows, illustrating part of the main valve assembly.

Figure 5 is a horizontal section of Figure 1 on the line 5-5 in the direction of the arrows, showing part of the valve containing block.

Figure 6 is a horizontal section through Figure 1 or 2 on the line 6-6 looking upward in the direction of the arrows.

Figure 7 is a horizontal section of Figure 1 on the line 7-7 in the direction of the arrows, showing a cross section of the dashpot chamber.

Figure 8 is a horizontal section of F igure 1 on the line 88 in the diiection of the arrows, or of Figure 9 on the line 8-8 in the direction of the arrows.

Figure 9 is a section in a vertical direction'similar to Figure- 1 of the lower end of the load compartment, showing the loading valve in its lowered, that is its discharged position. I

Figure 10 shows a vertical section of the pressure equalizing valve, showing it in open position, this being an enlargement of the valve as shown in Figure 1 in which it is closed.

Figure 11 is an elevation of the pressure equalizing valve in the direction. of the arrow 11, Figures 10 and 1'.

Figure 12 is a plan of a clamp used to hold the pressure equalizing valve closed while the bailer is being discharged at the top of the well.

Figure 13 is an elevation of a small bore tube which may be attached to the lower end of the load compartment, replacing the loading valve for use in collapsed casings.

Figure 14 is a modified form of loading valves to that shown at the lower part of Figures 1 and 9 in the same direction, and operates to agitate the material by its passage through the valve.

. ton 10.

. charging the oil chamber with oil.

Figure 15 is a bottom Viewv of Figure 14 in the direction of the arrow 15.

Referring first particularly to Figures 1, 1 2 and 3, the bailer comprises a cap section 1 which forms a housing 2 for a safety valve and stop cook, a tank section 3 forming the pressure tank 4, a valve-containing block 5, the upper section 6 of the oil chamber, the foot section 7 containing the lower part of the oil chamber 8 and the load compartment 9, separated by the separating pis- The base of the foot section is closed by the loading valve 11. The housing 2 contains the combined air charging valve 12 and stop cock, having the tube 13 leading through a head block 14 into the pressure tank 4. An aperture 15 is left in the cap section 1 to introduce an air hose to the tube 13, and is closed by a plug 16. An

allows operating the stop cock with a wrench. This is closed by a plug 18.

The pressure tankhas a relief or safety valve 19 threaded into the head block 14 and discharging into the housing 2. The cap section 1 and tank section 3 have a screw threaded connection 20 with gaskets 21 and. 22 between these sections and the head block 14. A valve rod 23 extends through the cap section 1 and in its passage through the air tank is contained within a valve rod tube 24. This rod has an upper section 25 connected thereto by a screw threaded coupling 26. Valve rod 23 extends through cap 1 to form a lifting stem 27 having an eye 28. The lifting stem is screw threaded as shown at 29 and has threaded thereon a nut 30 and lock-nut 31, there being a shoulder 32 on the lock-nut, with a compression spring 33 hearing there-against andagainst the top 34 of the cap.

The tube 24 forms an air and oil tight engagement with the head block 14 having a gasket 24 and contains a stufling box 35 through which the valve rod 23 may reciprocate. The lower end of the tank section 3 is connected to the "alve-containing block 5 by a screw threaded connection 36, and the valve at the upper end of the valve-containing block is in the form of a plate valve 37 in which the seating block -38 is brazed or otherwise secured to the block 5. Apertures 39 lead from the pressure tank 4 into the passages 40 in the block 5. A sliding plate 41 closes the aperture and is held in place by a compression spring 42, which is given the proper compression by means of a coll'ar 43, adjustable on the tube 24 and secured by a set screw 44.

A bore 45 leads downwardly from the passages 40 into the base of block 5, and

has a port' 46 leading to a slide valve 47. A

filling aperture 48 closed by a plug 49 leads into the bore 45', and is for the purpose. of The bore is closed at the bottom by a plu 50.

The slide valve 47 is guided between s 'des 51, and is held on the reduced lower end 52 of the valve rod 23, by means of a nut and lock-nut 53, screw threaded on the end 52. The valve is held tight against its seat by the spring 54 shown fastened by a screw 55 to the lower face of the block 5.

The dashpot 56 for controlling the open ing of the slide valve has a cylindrical bore 57 with a series of slots 58 cut in the wall at the upper end, andalongitudinal curved slot 59 at one side in the lower part. A piston 60 is adjustably mounted on the threaded end 52 of the valve rod, and is adjusted thereon by a pair of nuts 61 hearing on each side of the piston. The dashpot is secured in proper relation to the valve block 5 by screws 62 through the upper section 6 of the oil chamber.

The object of the slots 58 is to allow the oil in the cylindrical bore 57 to by-pass around the piston 60 in the operation of the dashpot and the object of the curved slot 59 at the base of the bore is to control the bypassing of the oil around the piston in conformity with the flow of oil through the port 46.

The quantity of liquid passing through a port or an orifice is expressed by the formula:

Where 9 is the quantity of liquid, 0 is a constant de ending on the viscosity of the li uid and t e nature of the orifice or port, a is the area of the port, 9 is the acceleration due to gravity and k is the head of liquid.

There will be a certain quantity 9 of oil passing through the port 46, for which the well tool is most eifective, and as the operative head depends upon the difi'erence between the pressure in the pressure tank and that in the well bore, as will be hereafter described, it is necessary to progressivel increase the amount of the opening 0 the port, that is of-the area a, to compensate for the decrease in It so as to maintain the q, that is quantity, at the most efficient amount, Following the above formula, the curved slot 59 is formed having areas for byassing the oil around the piston 60 in con ormity with the results worked out by the above formula "for different openings of the. port 46 and difi'erent hydrostatic heads.

- The return oil valve, to pass the oil from the pressure tank back to the oil chamber when the bailer is being unloaded at the top of the well, is formed as follows :-The valve containing block 5- has a duct 63 leading tion 65, the tube leading to a sto cook 66, having flanges 67 by which it is bo ted to the upper section, 6 ofthe oil chamber; the stop of the bailer as shown in Figures 1, 2, 3 and the various cross sections thereof. The details ofthe oil chamber and the load compartment with their immediate operative mechanism is as follows, having reference particularly to Figures 1", 9, 10 and 11, and

the several cross sections. The oil chamber 8 is contained in that part of the upper section 6 of the oil chamber, below the valve block 5, as shown in Figure 1, and the upper part of the foot section 7 above the separating piston 10. The upper and lower sections 6 and 7 are secured together by a screw threaded connection 71.

The piston 10 comprises a plate 72, packing cups 73, cup plates 74, a bolt 75 and securing nuts 76. The piston is free to move up and down in the oil chamber 8, and load compartment 9, as will be hereafter described, between thelimits of the upper stop bar 77 and the lower stop bar 78.

The pressure equalizing valve 79, shown in Figures 1 10 and 11, is positioned in the foot section 7, so as to be above the separating piston when the oil compartment is filled, and to be below the piston in the load compartment, when the bailer is lifting a load of sand. It is preferably situated slightly below the upper stop bar 77. A slot or groove 80 is cut in the face of the foot section 7, and at the mid section of this groove there is formed a circular valve seat 81, leading to a port 82 into the interior of the oil chamber 8. The valve is a circular disc 83, rigidly connected at its center to a stifi flat spring 84, which has a pair of thereby closes the port, and as the bailer is lowered in a well, the excess pressure outside closes the port 82 more tightly. The short slots 85 allow suflicient movement of the spring to open the port.

The clamp to hold the equalizing valve 79 closed, when the bailer is being discharged at the top of the well, is shown in Figure 12. It comprises two segmental sections 87 and 88, joined by a hinge 89 and a fastening clamp 90 which may be of any suitable design. A set screw 91 bears upon the disc 83 and may be tightened by i a wrench. The clampis of course removed before the bailer is lowered into the well.

The loading valve 11 is constructed as follows, having reference particu ar y to F ig-' ures 1 8 and 9. A heavy valve seat 92 has a tight fit in the bottom 93 of the foot section 7 and has a pair of stirrups 94 secured to each side of the valve seat and forming a segment 95 curved around the inside of the foot section 7. Each stirrup has a longitudinal slot 96, and engages two heavy pins 97 and 98 which are secured in apertures 99 and 100 in the wall of the section 7. The aperture 100 is screw threaded and each pin has a recess 101 to fit a suitable wrench. The pins are thus insertable and removable. As shown in Figure 1 the pins hold the valve 11 in fixed position while the bailer is being lowered and raised with a load, but when the upper pin 97 is removed, the valve drops onto the lower pin for discharging the load as shown in Figure 9. Any suitable valve may be used to co-operate with the valve seat 92, that shown in Figures 1 and 9 is of the type known as a dart valve, having a partly spherical valve head 102, a stem 103 depending therefrom, and a ball weight 104 projecting slightly below the lower end of the bailer.

In Figures 14' and 15 I show an alternative form of valve which operates to agitate the material by its passage through the valve. This is constructed with a bracket 105 secured to the stirrups and forming a guide through an aperture 106 for the upper stem 107 of the valve 102. The lower stem 103 pas'ses'through an aperture 108 in the bar 109 secured by screws or the like 110 to the valve seat 92. The churning weight 111 has a series of blades 112 formed on a bevel from top to bottom so that as the sand and oil in the bottom of the well is forced by the excess pressure in the well through the .valve, it will rotate the blades, thus causing a churning action. Some of the blades may be provided with lugs 113, and the center with a projecting point 114.

In order to bail sand in a partially collapsed casing or in other circumstances,

where the bailer is too large in diameter'to be lowered, a smll bore tube may be at tached to the load compartment as shown in Figure 13. In this case an annular ring 115 replaces the valve 11 and may be secured on the pins 97 and 98 by means of a stirrup 116, which in this case, is shown without a slot. A small bore tube 117 has a screw threaded connection 118 with the annular ring, and at its lower end is provided with a cutting point 119 and a suitable dart valve 120; a valve similar to that shown in Figures 14 and 15 made on the proper scale may be used. lVith this construction, the small bore tube 117 may carry the whole of the load depending on the length of the tube.

The manner of operation of my bailer and the method in detail is as follows When the bailer is at the top of the well,.

it is held supported by the ring 28, which by means of the valve rod 23 holds the sliding valve 47 upwardly and closes the port 46. The pressure tank 4 is filled with air through the air charging valve 12 and tube 13 to any desired pressure, in accordance with that found desirable for different hydrostatic heads in the well at the location of the bailing operation. It will be usual to fill the pressure tank with air at atmospheric pressure which merely means opening the stop cook 12. The safety valve 19 may be set at any desired blow off pressure, depending on the hydrostatic head at the point of bailing and the strength of the bailer, and is preferably set at such an amount that the transfer of oil of the oil chamber to the pressure tank will be retarded. The pressure tank 4 is considerably larger in volume than the oil chamber 8 so that there will always be a residue amount of air in the pressure tank even after the safety valve has been caused to blow off by the excess pressure in the well.

To fill the oil chamber 8, the slide Valve 47 is lowered, opening the port 46, the plug 49 is removed and oil poured through the filling aperture 48. The load of oil causes the separating piston 10 to descend to the stop bar 78. During this filling operation it is preferable to clamp the pressure equahzing valve 79 with the clamp of Figure 12 although the spring 84 is of suilicient strength to prevent much leakage of oil from the oil chamber 8. When plug 48 is replaced, and cock 66, air valve 12 and apertures 15 and 17 are closed, the bailer is ready for operation, it being preferable to fill the cap section with clean oil, since if the cap section were merely filled with air, the pressure at the foot of'the well would force oil, water and sand into the interior of the cap section, which would foul the valves and other elements. It will be understood that there will be sufficient looseness in the bearing of the lifting stem 27 in the cap 1 to allow passage of oil and of the air blown off from the safety valve.

The bailer is lowered in the well by a cable attached to the eye 28, and as above de scribed, this holds the valve rod 23 and the sliding valve 47 in its upper position, thereby closing the port 46. When the bailer strikes the bottom of the well, or the material to be removed, there is no tension on the cable and hence the compression spring 33 is free to function. This spring presses downwardly on the shoulder 32 of the lock-nut 31, thereby depressing the valve rod 23 and the sliding valve 47. The rate at which this may descend and open the port 46 is governed by the tension put into the spring and the rate at which dashpot 56 operates. The manner in which the piston 60, of the dashpot, desgends in the cylindrical bore 57 is de cribed a. we.

As the port 46 opens, the excess pressure outside the bailer in the well, forces the sand and consolidated material through the valve 11 into the load compartment 9. This compartment is, of course, full of air as it descends in the well and the separating piston 10 is forced upward by the excess pressure causing the oil in the chamber 8 to flow in the port 46, up through the bore 45 and the passages 40 and the valve containing block 5, then through the apertures 39 in the seating block 38, lifting the plate 41 and flowing into the pressure tank 4.

Presuming the air in the pressure tank is at atmospheric pressure before the bailer is lowered into the well, and that the safety valve 19 is set at 1000 pounds er square inch, then, as the oil flows upward from the oil chamber 8 to the pressure tank, the air becomes compressed until it reaches the pressure of the liquid at the-point of bailing. As before mentioned,the pressure tank is of considerably larger volume than the oil chamber, so that when all of the oil has passed into the pressure tank there will still remain space for the compressed air. It is manifest that as the separating piston is forced upward, and the oilin the oil chamber flows upward, that the load compartment will become filled with the material being bailed.

The equalizing valve 79 functions during the lifting of the bailer with its load. As above described, the separating piston is stopped in its upward motion by the upper stop bar 77, which will leave the equalizing valve below the piston, and in the load compartment. The pressure therefor, in the load compartment will be the same as that at the place of operation in the well,- and may be in ordinary operation up to 2,000 pounds per square inch.

When the bailer is lifted, the ressure in the load chamber equalizes with t e decreasing pressure outside the bailer through the equalizing valve 79. During this lifting operation the downward passage of oil or clean liquid from the ressure tank is revented by the late 41 an stop-cock 66. he pressure in t 8 pressure tank, when it emerges at the surface of the liquid in the hole, will be the pressure for which the safety valve is set, or the pressure of the bottom of the hole if the safety valve is set for a ressure in exfesis of the pressure of the ottom of the On drawing the bailer above the derrick floor, the clamp of Figure 12 is placed on the equalizing valve and to dischar e the load, the upper pin 97 is removed, a lowing the valve 11 to drop as shown in Figure 9. In order to positively force the load out of the load compartment 9, the stop cook 66 is opened by turning the valve 68 b a wrench through the aperture 69. This all ows the oil in the pressure tank to pass through the duct 63 and tube 64, and the outlet port 70 into the oil chamber. The high pressure of the air in the pressure tank aids this operation.

opening the air charging valve 12,,highpressure air could be used to completely clear all the oil out of the pressure tank.

WVith the air tank again charged at the desired air pressure, and the various valves set in their normal operating position, the bailer is ready for another bailing operation.

The method of operation and the structure of the bailer may be considerably modified and further changes could be made to suit special circumstances or conditions without departing from the spirit of my invention. It is to be understood that my bailer could be used for bailing sand in a water well and it may also be utilized to bail sand and water from the bottom of an oil-well; moreoverI can use a clean liquid such as water in the so-called clean oil chamber.

Itmay be further stated in regard to the safety valve that aftenit is set (say for one thousand pounds per square inch), nothing happens which effects the operation of filling the tool at the bottom of the hole. When the valve 47 is opened the pressure in the bottom of the hole rushes into the tool and compresses the air in the pressure tank against the head 14 until it is equal to the pressure in the bottom of the hole. If this pressure is in excess of the amount, (say for one thousand pounds per square inch) for which the safety valve was set, then this excess will be discharged as the tool is withdrawn from,

the hole when and only when the tool reaches the level, in the liquid in the hole, where the hydrostatic head equals the excess of the pressure in the pressure tank over that for which the safety valve is set. In the above example if the pressure in the bottom of the hole was fifteen hundred pounds per square inch, then the safety valve would begin discharging when the well tool reached the level, upon being withdrawn from the well, where the hydrostatic pressure is 500 pounds per square inch. From that level the safety valve would continue to discharge, as the bailer continued to be hoisted, until at the surface of the liquid the pressure inside the pressure tank would be reduced to the value for which the safety valve was set.

Having described my invention, what I claim is 1. A well bailer comprising a load chamber and an oil chamber, and means for varying the size of said chambers, said-means being responsive to the difi'erence of pressure between said chambers.

2. A well bailer comprising a load chamber adapted to receive material to be bailed, an oil chamber positioned above said load chamber, and a movable member between said chambers and adapted to move in response to a difference of pressure between said chambers.

3. An oil bailer comprising in combination a cylinder containing an air tank, an oil chamber and a load compartment, a valve between the air tank and the 'oil chamber, means for closing said valve, and means for opening said valve when the bailer reaches the point of bailing, whereby the excess pressure in thewell over that of the air in the air tank compresses the air and forces sand into the load compartment.

4. An oil bailer comprising in combination aholder containing an alr tank, a load compartment, a valve forming an operative connection between the air tank and the load compartment, a lifting stem to hold said tank and fills the load compartment with sand in proportion to the decreased volume of air.

5. An oil bailer comprising in combination a holder containing an air tank, an oil chamber and a load compartment, a valve between the air tank and the oil chamber, means to hold the valve closed, and means to open the valve when the bailer strikes an accumulation of sand, whereby the excess pressure in the well displaces oil in the oil chamber into the air tank, and forcessand into the load compartment.

6. An oil bailer as claimed in claim 5 having a separating piston between the oil chamber and the load compartment.

7. An oil bailer as claimed in claim 5 having in addition means to regulate the rate of. opening of the valve.

8. An oil bailer as specified in claim 5, having in addition a valve control device consisting of a dashpot, a piston operatively mounted in said dashpot, and a rod connecting said valve and said piston.

9. An oil bailer comprising in combination an air tank, an oil chamber, a load compartment, a valve between the air tank and the oil chamber, a separating piston between the oil chamber and the load compartment, a lifting stem connected to the valve, adapted to hold the-valve closed while the bailer is being lowered, and a spring to open the valve when the bailer strikes accumulated sand.

10. An oil bailer as claimed in claim 9, having in addition a plate valve forming an inlet to the air tank, and retaining the oil .bailer, means to open the valve to discharge the load and means to pass oil from the air tank into the oil chamber, and thereby force the separating piston downwardly.

12. An oil bailer comprising in combination a shell, a separating piston slidable in the shell, and dividing the shell into a load compartment and an oil chamber, means to allow displacement of oil in the oil chamber upward in the shell, and thereby allow sand to be forced into the lower end of the shell.

13. An oil bailer as claimed in claim 12, having in addition a valve at the lower end of the shell forming with the separating piston, a closed load compartment when the bailer is loaded, and an equalizing valve to relieve excess pressure in the load compartment, as the bailer is removed from the well through the liquid therein.

14. In a well bailer, a shell, an equalizing valve comprising a port through the shell, a valve to close said port and a spring to normally retain the valve against the valve seat.

15. In a well bailer, a shell, an equalizing valve in the shell, comprising a slot in the shell, an aperture from the slot to the interior of the shell, forming a port, a valve in the form of a disc, a valve seat surrounding the port and a flat spring secured in the slot adapted to hold the valve against the valve seat.

16. In a well bailer, a shell, a load compartment, a valve at the base of the shell having a removable valve seat, vertical supporting members connected to the valve seat, a pin removably secured through the shell, and in operative connection with the supporting members, adapted to hold the valve seat up thereby closing the load compartment, or in lowered position, thereby opening the load compartment.

17. In a well bailer, a shell, a load compartment, a valve at the base of the shell forming a closure for the load compartment, a removable valve seat forming part of the valve, stirrups extending upwardly from the valve seat, contiguous to the shell, a slot in the stirrups and a pair of pins through the shell, and engaging in the said slot, the upper of said pins being removable to drop the valve seat below the end of the shell.

18. A well bailer comprising a pressure tank, an oil chamber, and a load chamber, means for admitting material under pressure into said load chamber, and means actuated by said material to force oil from said oil chamber into said pressure tank.

19. A well bailer comprising a pressure tank, an oil chamber and a load chamber,

means for admitting material under pressure into said load chamber, a piston mounted between said load chamber and said oil chamber and adapted to be moved upwardly by the pressure of said material, whereby oil will be forced from the oil chamber to the pressure tank until the pressures in the pressure tank, the oil chamber and the load chamber become equal.

20. In a well bailer having two compartments, a passage between said compartments, a valve to close said passage, a dashpot having a piston operatively connected to said valve and a cylindrical member to receive said piston, said cylindrical member having a longitudinal slot on its inner surface to form a passage whereby a liquid may pass from one face of the piston to another.

21. A well bailer as specified in claim a tank adapted to contain oil above the load compartment, and a duct having a valve leading from the tank, said valve being manually operatable to open the duct, and pass the oil downwardly and thereby displace the load in the load compartment in a dumping operation.

23. A well bailer as specified in claim' drical shell, means to close the ends of said shell, the interior of said shell being divided into a plurality of chambers, said chambers including an upper chamber having an outlet whereby the pressure in said upper chamber will be maintained equal to the pressure outside said shell, a pressure tank adapted to receive air under pressure, an oil chamber, and a load chamber adapted to receive material to be bailed, a safety valve between said upper chamber and said pressure tank, a

sliding valve between said pressure tank and i said oil chamber, and a sliding piston between said oil chamber and said load chamber.

In testimony whereof I aflix my signature.

OMAR A. GAVIN S.

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