US1607239A - Method of and apparatus for pumping an oil well - Google Patents

Description

Nov. 16 1926A` 1,607,239

W. H. CLAPP METHOD 0F AND APPARATUS FOR PUMPING AN OIL WELL Filed Oct. AS51I 1925 6 Sheets-Sheet l www Wwf/TOR; M/ML /vf CLA/DP, 5y

MA Aagf/EK Nov. 16 1926.

W. H. CLAPP METHOD 0F AND APPARATUS FOR PUMPING AN OIL WELL Filed oct. l51, 1925 6 Sheets-Sheet 2 A TMB/V214 Nov. 16 1926.

1,607,239 w. H. -cLAPP METHOD 0F AND APPARATUS FOR PUMPING AN OIL WELL n.5: Ltg-4 Filed Ootf 31, 1 925 6 Sheets-Sheet 5 n Figc/ff.

Nov. 16 1926. 1,607,239

w. H. cLAPP l METHOD OF AND APPARATUS FOR PUMPING AN OIL WELL A Filed Oct. 51, v153,255 6 Sheets-Sheet 4 i M//LL H (2A/2p,

Nov. 1'6 1926 w. 'H. cLAPP METHOD OF' AND APPARATUS FOR PUMPING AN OIL WELL Filed Oct. 3ll 1925 6 Sheets-Sheet 5 CRA/w( a P/rMA/v Cum/E A Cum/E5 fDEAL M//v/MUM 5 71e E66 TIME //V SECO/V05 UP DOW/V x D/SPLA EME/v T /N FEET Nov. 16 1926.

` w. H. CLAF'F` METHOD 0F AND APPARATUS FOR PUMPING AN OIL WELL Filed oct. s1, 1925 s sheets-shewr e ffy: 16-

L# y. wl' @W Mw Ma w M MH W m fu /A A .o ,m y E Lwmlfw H 5 E. 1w @l M L 5, W A @t f .LNVAIwSLILImIJA upon the maximum stress, maximum stress Patented Nov. 16, 1926.

raras WILL H. CLAPP, PASADENA, CALIFORNIA.

Application led October 31, 1925. Serial No. 6,111.

My invention relates to the oil producing industry, and'it relates inl particular to oil Well pumping equipment.

A common forni of pumping used for taking oil from the ground has a pump barrel which is placed near the bottom of a well and which isI attached to the lower end. of a pump tubing. The pump tubing-extends into the well from the surface of the ground. Adapted to reciprocate in the pump barrelis a pump plunger which is attached to the lower end of a string of sucker rods. The string of sucker rods ex` tends through the pump tubing and a stuffing box secured at the upper end of the pump tubing, and is connected to one endof a D a walking beaml pivoted on a Samson post which is placed on the floor of the derrickv of the well. The walking beam is oscillated by a walking beam crank whichis secured to the shaft of a band wheel, the walking beam crank being connected to the end of a walking beam opposite to thev string of sucker rods by means of a pitinan.- When the walking beam is-in operation the pump plunger is reciprocated `(through the inter-connect-- ing mechanism), thus pumping oil to the surface of the ground through the pump tubing.

One of the foremost deficiencies in this type of pumping equipment is the breakage of the string of sucker rods. This type of breakage of the string of sucker rods, subjected to variable stresses, is what is known as fatigue failure or progressive fracture. which occurs as follows:l Under the stresses of a varying load some 'part of the rod where there is a local weakness (as a kink or a scratch on the metal surface which brings about a localized stress of high intensity) will start to fail. This failure will consist in a crystals age planes. This fracture sets up a stress of high intensity in lan adjacent crystal which in turn will fail, and so on until the metal severs at this place. l

It has been demonstrated that -this character of failure is greatly effected in three different manners by the stresses placed on,

first, it depends the string'of Vsucker rods;

the higher the ltake place; second, it is a function of the equipment.

fracture of oneof the minute-j of the metal along one of its cleav`Y the sooner. the break Will-- range of stress, the greater the di'erence between the maximum and minimum stresses,

the sooner the failure will occur; third, it

is dependent upon the abruptness withwhich the loadis givento and taken from the sucker rod string'. It is demoiistratable that a load instantly applied will' produce twice as great a stress as though it had been appliedgradually. Of course, failure also depends on repetition of Variable loading.

The forces which make up the Variable load on the upper end ofthe strii'ig`of suck# er rods consist of (l) the weight of the sucker rods and the plunger mechanism, (2) the weight of the column of oil being lifted, (3) frictional resistances, and (4) inertia .forces whose value depends on the weight being lifted and the character of the'motion of the pump plunger and string of sucker rods. There is only one of these four forces which can be modified to obtain more ideal stress conditions, and this is the inertia force whose value can be changed b modifying the character of themotion o the stringg of sucker rods and pump plunger.

The motion of the string of sucker rods s y and pump plunger in` an ordinary crank mechanism is identical in character with that of an engine cross'head in which thev strokes are the same in length and number per minute, and in whichthe ratio of the connecting rod length'to the crank length is the same as the ratio of the pitman length to the walking beam crank length. The pump, therefore, starts its stroke at. zero velocity, accelerates to maximum at the midzero at the end of the' stroke. Since the inertia force varies directly proportionally to acceleration, then the inertia vforce of such a motion of the pump will cause a high maximum load, a large range of maxi-` also willl t stress placed 'on the sucker rods will be lower and the range of maximumV and minimum loads will be less than in the ordinary pumping equipment. f

It is another object of this invention .to provide an apparatus oftlis` characterin dl'e' of the stroke. and decelerates again to which there will be no abrupt change in loads placed on the string of sucker rods. It is a further object of this invention .to provide an operating apparatus of this chara'cte'r having a piston which is connected directly to the walking beam.

It is also an object of this invention to provide -a pump operating apparatus in which the piston is operated by compressed l0 air which is admitted during .a greater part of its down stroke. The piston is n accelerated while the air is :admitted and decelerat'es while air expands after the supply of air to the cylinder has been discontinued.

It is a further object of my invention td provide a pump operating apparatus of this` character in which the piston is allowed to rise by releasing air from thecylinder.

p "2" It is a still further object of this invention to provide a pump operating ap-partus in which the piston compresses the air in the cylinder during the later portion of its up stroke, being thereby adually decelerated. It is an additional o ject of this invention tol provide a pump operating apparatus in which compressed air may be admitted to the cylinder as the piston nears the upper end of the stroke, thereby completing the gradual ydecelerationl of the piston to zero velocity and then reversing its direction of motion. l It is a further object of the invention to provide a .pump o eratin apparatus of this character in whic the a mittance to and the exit of air from the cylinder is controlled by a slide valve, which slide valveis oper- -ated -by means associated with the piston. It is another objectof this invention to provide apump operating means of the character mentioned in Vwhich a means for operating the slidev valve is adjustable so that satisfactory periods of acceleration and deceleration of the piston may be acquired, so that the plunger of the p-ump being operated may have a desired motion.

lt is-a still further object of this invention to provide a` pump operating mechanism which will have a high mechanical e`ciency 59 as compared with the ordinary drive. An additional object of this invention is to provide a pump operating apparatus which will be comparatively cheap to op-y erate.

5f y It is an ddaiahai Object O'f the invention to provide a pump' operating mechanism of the character mentioned having a piston of variable stroke and speed under direct control of the operator, the length of the stroke being governed by the cut-off and the speedv by the adjustment of the pressure regulating valve. i v l I t is a still further object of the invention to provide a pumpoperatin mechanism of the character mentioned rom which an indicator card may be made which will inform the `operator of certain conditions in the well.

4Other objectsl and advantages of this in- Xf'entionwvill be made-evident hereinafter. Referrringto the six drawings in which I illustrate a'preferred form of my invention: p Fig. l is a diagrammatic View illustrating all of the parts of my invention and illustrating the utility thereof.

Fig. 2 is an lelevational View of a pump operating mechanism of my invention.

Fig. 3 is an elevational sectional view taken as indicated by the line 3--3 of Fig. 2. Fig. 4 is a section taken; as indicated by the line 4 4 of'Fig. 3.

Fig..5 is a partial plan view of Fig. 3. Fig. 6 is a section taken on the line 6-6 of Fig. 3.

Fig. 7 showing clearly the slide valvev arrangmentand operating mechanism therefor,`which comprises an important part of my invention.

Fig. 8 is a section of the valve and its control mechanism taken substantially at right angles to Fig. 7.

Fig., 9 is a diagrammatic view illustratingthe positionsof the various parts of my sinvention at the start of the down stroke.

Fig. 10 is a diagram illustrating the positions of the'parts at the. end of the maxi- .mum acceleration of the down stroke of the pump operating mechanism.

Fig. 11 shows the positions of the parts at t-he bottom of the down stroke.

Fig. 12 shows the vpositions of the parts at the end of the' acceleration of the up stroke of the mechanism. f

Fig. 13 shows the positions of the parts near the end of the .up stroke.

Figs. 14, 15, 16 and 17 are graphic diagrams illustrating the results of' my inven' tion as compared with ,present pumping equipment.' f

The essen-tial parts of the pump operating mechanism of-my invention are shown in Figs. v2 to 8 inclusive. With 'reference particularly to these figures, my invention provides a base 20 which is supported on a foundation 21. The) base 20 consists of a lower casting 22 tod which a vert-ical housing 23 is secured. The housing 23 has an upper casting 24 secured thereto. The casting 24 has a central cylindrical opening 25 through whicha lower extending lip 27 of the cylindrical lcasting 28 extends. The 'cylindrical casting 28 is secured to the upper casting 24 of the base 20 by means of bolts 29 which are secured to the casting 24 and extend through a flange 30 provided by the cylindrical casting 28. The cylindrical casting 28 provides a cylinder 32 and a valve chamber 33 which is' positioned directly is an enlarged sectioned detail cylinder 32 is a p1ston'38.

adjacent to the upper end of the cylinder' 32. The upper end of the casting 28 has a cap 34 secured thereto by suitable `bolts 35, this cap 34 closing the upper end of the cylinder 32 and the Valve chamber 33.

Adapted to reciprocate vertically in the A piston rod in the form of a tubular member 39 is secured t0 a lower-'face of the 'piston 38 by a flange 40, this flange 40 being secured in place by cap screws 41.

placed inside the base is secured *to the lower end of the piston rod 39 by meansof a lower flange 44. Thev crosshead 43 has arms 46 in which bearings 47 are provided' through which vertical guides 48 extend. rlhe lower ends of the vertical guides 48 are rigidly secured in the foundation 21. The

upper ends of the guides 48 extend through projections 49 formed at the lower end of the cylinder casting 28 and have. nuts 50 `secured to the upper end thereof. Rubber `strike in event bumpers 51 are provided around the guides 48 just below the upper casting 24, against which upper faces of the bearings 47 may that the piston 38'should move above its normal stroke. Similar rubber bumpers 52 are provided around` the guides 48 just above the base casting 22, against which' lower faces of the bearing portions 47 of the crosshead 43 lmay strike in event that the piston 38 should move below its normal stroke. Y

Bearing pins 53 are secured-to the outer ends of the arms 46, these'bearing pins having lower ends 54 of vertical reins 55 pivoted thereon. These reins 55 extend up'- ward and outward from the base 20 through openings 56 formed in the upper casting 24. The upper ends of the re-ins 55 are secured by nuts 58 to a suitable construction 59, by means of which the reins may be connected to ay walking beam .60 of a dei-rick 'equipment. `The construction 59 may Abe provided with vertical arms 61 which are secured to a shaft 61a which is supported at one end of the walking beam 60.

fAs clearly shown in Figs. 3, 7 and 8, a sleeve 62 is'secured in the upper-portion of the vvalve chamber 33. Openings 63 through this sleeve 62 connect the interior thereof with the passage 64 and the port 65 in the upper end of the cylinder 32. A slide valve 66 is adapted to operate in the valve chamber 33. This slide valve 66 is provided in the form of a shellr`67 havingjupper andl y of the chamber 33, respectively, which ends vses 68 are connected by a neck"69 which is of smaller diameter than the portions.,68. The

arms 70 which exshell 67 is supported by v -This arrangement tend inward to hubs 71.

provides a passage 72 whi'ch'extends entirely through the slide valve 66. The -hubs A cross head 43 the block 75.

71 are secured by nuts 74 on avvalve rod 73 'which extends through the chai/uber 33.

provided with a block 75 having a pair of lower shoulders 76 land a pair of upper shoulders77 as shown in Fig. 7. A pair of vertically extending'tappet rods 80 are securedvto an arm 81 of the cross `head 43. These tappet rods extend through openings 82 formed inthe upper casting 24 and they extend adjacent to and at each side of v the valve rod 73."'Adjustably secured to the tappet rods 80 are a pair of lower or deceleration tappets 84 and a pair of upper or/ up stroke tappets 85. These lower and upper tappets 84 and 85 are adjustably secured to the tappet rods 80 so that certain adjustments in theoperation of the apparat-us may be made. described later.

Secured to an upper face of the upper casting 24. is a bracket 87 which supports pins 88 on which dogs 89 are pivotally secured. These dogs 89, as shown in Fig. 7, are substantially the reverse of S shape.

The upper ends 900i'A the dogs 89 are positioned so that they are capable of engaging the lower andvupper shoulders 7 6 land 7 7 of'A The lower arms 91 are positioned so that they-may be engaged by inner faces92 and 93 of the lower and upper tappets 84 and 85, respectively. y

Compressed air is supplied to the central part of the valve chamber 33 surrounding the neck 69 of the valve 66 by means of a pipe 95, and air is taken from the valve chamber 33 near the lower part thereof by a pipe 96. The upper end of the valve rod 73 extends through an opening at the upper end of' the valve"cha1nber 33 This, however, will be 98 formed and has a lift plunger 99 attached thereto. l

This lift plunger 99 operates in a cylinder 100 provided by a member 101..,w'hich is cured tothe cap 34 by suitable cap screws 102.

A hole 106 is formed through the wall of the member 101 at a point opposite the position occupied by the lower end of the plunger' 99 when valve 66 covers and-closes the openings 63. A-small hole 107 through the wall of the member 101 communicates the lower end of the cylinder V100 with the atmosphere. The valve rod 73 has a sleeve 104 secured thereto by a nut 105 at the place where it extends through the opening" 98 at the upper end of the valve chamber 33. A pipe 108 is connected to the valve chamberI 33 adja-i cent to the air inlet 95. A branch 109 of this pipe 108 connects with the upper part of the opening 98. The branch 109 is provided with a valve 112 having a lever 113 which is adapted to be vengaged and operthe upper end 68 ofthe y ated by a lift tappet 115 whichis secured near the upper part of one of the tappet rods 80. This lift tappet 115'is adapted to engage the lever 113 and open the valve 112 when it moves upward past the level' 113 and close the valve 112 when it moves downward past the lever 113. The ope-ration of the valve is effective in supplying air to the cylinder 100 below the lift plunger 99.

The pipe 108 as shown in'F ig. 3 connects with the upper end of the cylinder 32 through the cap 34. The pipe 108 has a valve 117 placed near the end which connects with the cylinder 32 which may be operated to supply compressed air to the upper end of the cylinder`32 in case the piston has moved beyond its upper limit. This will be explained later.

I he pump operating mechanism, )ust described, 1s connected to o1l well equipment as 1 shown in Fig. 1. The walking beam 60 is pivoted on the upper end of a Samson post- 130 which is a part of standard equipment V'ot' a derrick 131. AThe end ofthe walking beam 60, opposite from that end to' which the reins 55 arenattached, has a polish rod vstantially as follows 132 attached thereto. This polish rod 132 passes through a stuiling box 133 and extends into the upper end of a pump tubing 134. The polish rod 132 has a stringof sucker rods 135 connected thereto" which extends downwardly through the pump tubing 134v to theplunger, not shown, of 'an oil well pump 136, placed at the bottom of a well 137. The inlet pipe 95 which suppliescolnpressed air to the valve chamber 33v extends from a compressed air reservoir 139 which is supplied with compressed air by means of a compresser141, the pipe'95 having a regulating valve 140. The compressor 141 is connected to the reservoir 139 by a pipe 142 having a relief valve 143. The compressor 141 is preferably operated by av gas driven engine or Diesel engine 144. The air outlet 96 extends to a low pressure air receiver 145, and the low pressure air receiver 145 is conneeted to the compressor 141 by means of a pipe 147.

The operation of my invention is sub- In Figs. 2, 3, 7, 8 and 9 I show the' position of the various parts of the pump-operating mechanism at the beginning 'of the down stroke. The slide valve 66 is positioned (in these figures) so that the port is in communication with the air inlet pipe 95. Compressed air passes through the pipe 95, the adjacent portion of the valve chamber -33 and through the port 65 into the updogs 89. These dogs 89 are at this time in engagement with the lower shoulders 76 of .the block which is secured at the lower end of the valve rod 73. The compressed air, being admitted to the upper end of the cylinder 32, forces the piston 38 and its asoccupy the positions as .shown diagrammatically in Fig. 10. This motion of the piston 38 eomprisesethe period of maximum acceleration of the down stroke thereof.

When the `piston arrives at the position shown in Fig. 10, the lower valve tappets 84 secured to the rods 80 will have moved finto such ositions as to engage the lower arms 91 of the dogs 89. The dogs 89 are swung by the lower tappet 84, causing the upper arms 90 of these dogs to disengage the lower shoulder 76 of the block T5. This disengagement allows the slide Valve 66 to move downward under force of gravity and the additional downward force duc to thel fact that the lower Aenlarged end 68 of the valve 66 is larger than the upper enlarged end 68 thereof, so that the pressure in the space surrounding the neck 69 exerts an unbalanced downwardl force on the valve 66.

As the ,tapp'ets 84 move past the dogs 89,

the cylinder 32.' The upper enlarged por-- tion 68 of the valve shell 67 closes this port 65. This position of the valve stops the suply of air to the cylinder 32. The air which has already been supplied to the cylinder 32 .sociated parts downward until these parts willexpand and the piston will move to the lower end of its downward stroke, this .position being shown in Fig. 11. The movement of the piston during the expansion of the air in the cylinder 32 comprises the period of maximum deceleration of the down stroke of the piston 38.

When the piston 38 has reached its lowv ermost position, the upper tappets 85 will have moved into such a osition as to engage the lower arms -91 o the dogs 89. and

vto swing them out of engagement with the upper faces 77 of the block-7 5. Thls allows' .the block 75 to move downward so that the inner faces of the upper arms 90 of the dogs 89 will rest on faces 150 yof the block75. This disengagement of the dogs 89 permits the slide valve 66 to move into its lowermost position so that the upper end thereof is below the port 65. The port 65 is thus communicated with the air outlet pipe 96 by means of the passage 72 through the valve 66.' As the air passes from the cylinder 32 the piston 38 will move upward. u

From an inspection of Fig. 1, it'wlll be seen that during a down stroke of the piston 38 theplunger of the pum 136 ismoving through its up stroke and t at during an upv stroke of the piston 38 the pump plunger is moving through a down stroke.

Therefore the weight of the pump plunger pulls upward on the piston 38 and causes it to move upward when the air outlet pipe 96 is connected with the upper end of the cylinder 32.

rlhe piston, with its associated parts,

moves upwardly until it reaches a position,

`valve 112. High pressure air immediately flows through the pipe 109 into lthe opening 98 and thelcylinder v100. The pressure. thus b uilt'up in the cylinder 100 raises the plunger 99 and the associated valve parts, as shown in Fig. 12. s'soon asfthe upper end 68 lof the4 valve 66 has closedV the openings 63 connecting with the port 65, the upper end of the sleeve 104 moves past the pipe 109 and cuts off the supply of air to the cylinder Y100. The compressed air in the cylinder 100 eXpanids, forcing the plunger 99 further upward until the lower edge thereof uncovers the hole 106 and releases the air to atmosphere. At this point the upper shoulders 77 of the block 75 are in a position slightly above the ends of the armsv l90 of the dogs 89 so that the latter move -into position below these shoulders 77. rlhe air in the cylinder. escapes through the hole 106 and the small hole 107 to atmosphere',

v reducing the upward pressure on the plunger 99 and permitting the valve to settle until 'the shoulders 77v rest on the dogs 89, as shown in Fig. 10. ln thisposition the upper end 68 of the valve 66 cuts off the cylinder 32 from the valve chamber 33u, so that, as the piston 38 continues itsupward movement, the air in the cylinder 32 is com-4 pressed and resists with increasing forcel the motion of the piston 38, graduallydecelerating it.

As the piston 38 approaches the end ofv the up stroke, a dash pot 156 mounted on v the arm 81 of the cross .head 43 engages the lowerend of the valve rod 73 and raises it and the 'vaive 66, as shown in Fig; 13, admitting high pressure air from the valve chamber to the cylinder 32 above the piston 38. This high pressure acting upon the piston 38 completes the gradual deceleration 'to zero and reversal in direction thereof, as

indicated in Fig. 9.

As the piston 38 reaches the end ofthe up stroke the dash pot 156e carries thef valve rod 73 upward to a position in which'the shoulders 76 of the block 75 are slightly above the ends of the arms 90 of the dogs 89, so that the latter drop into position beneath the shoulders 76. When the piston reverses direction and starts on its down' stroke the dash pot 156 ceases to support the valve rod 73, with the result that the valve assembly moves downward until the shoulders 76 rest on the dogs 89, as shown in Figs. 2, 3, 7, 8' and 9. In this position the apparatus is in position to start anew the cycle just described.

By making the lower tappets 84 adjustable it is possible to change the time at Whichthe valve 66 will close the port 65 and thus change the period of accelerationl of the downstroke of the piston 38. By making the uppertappets 85 adjustable in position it is possible to varyv the time at which the air is exhausted from the cylinder 32, thus changing the position at which the piston starts on its up stroke. In this manner the length of stroke of the pump may be changed. Likewise, the position of the 4tappet 115 may be changed in order to change the time at Which the port is again closed and the compression begins to decelerate the piston. v'llhe relation of the dash pot 156 and valve rod 73 is not adjustable; in service it'Will generally be most desirable to set the tappet 115 so that the compression will begin at such a point in the stroke that the pressure at the end of the stroke will be substantially equal to the admission pressure. rlhis is advan tageous from the standpoint of greater thermal eiiiciency and gradual change of decelerative force, and reduces the function of the dash pot 156 to opening the valve to L admission at the end of the stroke.

lf, however, through improper adjustment 'of the lift tappet 115 or failure of the lift plunger 99 to function properly, the port 65 should not be closed soon enough yfor a compression to be built up to a suf. ficient magnitude to stop the piston 38 at its normal uppermost position` the dash pot 156 will lift-the valve 66 and open the port 65 to admission pressure. This permits the cylinder 32 above the piston 38 to fill with air at admission pressure, providing a large butnot violently applied deselerating force. rlhis force may be suiiicient to stop the piston 38 before it reaches the port 65; if not, the piston 38 may cover and close the latter. llnA this case, further movement ofthe piston 3 8r'apidly increases the compression to such .a point that it is quickly brought to rest. rl`hus,in this extremecase, the dash pot 156 serves as an` emergency means for openingtlle port'65 to provide a cushion of high pressure air, lduring the further compressing ofl lwhich the lpiston 38 is stopped.l

Sometimes, during preliminary adjustments of themechanism, the piston 38 will overrun the 'port 65 as outlined in the previous paragraph. ln any case, when the pis:v

lll() rae ton 38 is at rest in a position above the port 65, it is only necessary to operate the valve 117 to supply air to the extreme upper end of the cylinder 32 so that the piston 38 may be returned and the port 65 opened.

Y In order to have a clear understanding of the advantages of'my invention it is necesment and the character of t-he results of the )lunger when it is operated by my invention. lhe steps taken to arrive at the motion produced by my invention should also be understood. For this purpose and for the purpose of comparing the results of my invention with results of present equipment, recourse is had to Figs. 14 to 17 of the drawings.

Let 'us firstconsider the ordinary crank and pitman arrangement. In Figs..14,'15

. sible to reduce I1.

and 16 I show curves illustrating how the forces on the upper end of th-e string of sucker rodsvary during the up and down strokeot` the-pump. There are four forces which make up the resultant force vP which stresses the rod at 'any instant. These forces `are Wr which is the weight of the sucker rod and plunger mechanism, Wo which is the Weight of the column of oil that has been lifted, F1 and F2 which are frictional resistances on the up `stroke or down stroke, respectively, and I which is the inertia force whose value depends upon the weight being lifted and the character of the motion of the plunger.

i -In the diagram of Fig. 16, P1 re resents the force acting upon the upperen' of 'the sucker rod when the pump begins its iup stroke, P2 represents the force at the end ofQ the up stroke, P3 represents the force at the beginning of the down stroke and P4L represents the `force at the time of the down stroke. P represents the force acting upon the upper sucker rodat any position of the stroke. Under the stresses produced by the variable force, P, which in this case Varies from a maximum of 10,210 pounds plus frictional resistances to a minimumof 2,690 pounds minus the frictional resistances, with an abrupt change in the load at the end of each stroke, the stresses on the sucker rods .which tend to produce fracture thereof are large.

veg ext, let us'referto Fig. 17 which is a P step in arriving at the form of motion ofmy invention. Since it ispo'ssible only to alter the inertia forceI by a modificationl of motion in the lunger it will vbe seen that P1 can be reduced in the same amount that it is pos- The inertia force I `varies directly withfthe acceleration and in4 fact Weight is to be raised through a distance S, f

Fig. 16, in a given time T the acceleration will be least When it is maintained at a constant amount throughout the interval, but in, this case the body would notl be brought to rest but would be traveling at-its highest speed at the end of the stroke. If the acceleration is maintained constant to mid-stroke an. equal deceleration will be required to bring the body to Irest. In Fig. 17 I show a diagram of forces acting on the rod when thev accelerating force is carried somewhat beyond mid-stroke. The same weights and time of raising are assumed as in Fig. 16. By carrying the acceleration beyond midstroke the inertia force I1 is reduced materially While I2 is increased in amount. Thus it will -be seen that the maximum stress'on the rod may be reduced and the range between the maximum and minimum lstress of the rod may also be reduced. If the return stroke is made in the same time and in the same manner We see that I3 bears the same relation to I1 as the weight Wr being lowered does to the weights 'Wr Aand, Wo being raised which, for the particular case We are considering makes I3 equal to 4/7 of I1. Simi-v larly, IA1 equals 4/7 of I1. The result of this change in. character of motion is to decrease "both the maximum load P1 and the rangeoi load P1-`P3, and it will be apparent that this improvement will be further promoted by using a still smaller acceleration on the up stroke and continuing it for a longer porvtion S1 of the stroke, carrying'this outuntil the final force P2 becomes equal to P8. To go further isto make P2 less than Ps and this Will'increase the range of stress due to the ditte-rence between maximum and -minimum loads.

P1 still further but at the expense of P3 but,

if one also continues to keep P2 equal to P3 by still further increasing the ratio` of S1/S2 equals S8/S4), the effect is to increase P1'as 1 decreases. Such increase can be carried out advantageously until P4 equals P1. Now;v these are the relationships which should exist in order to have the least maximum load and the least range of load onthe e sucker rod,viz, P1 equals P,1 and P2 equals curvemin whichP1 equals P1 and (P1 equals P Yisshown at C in Fig. 14.-. By assuming this curveC it will be seen-that the load changes abruptly near each end of the stroke .and it is known that abrupt changes of loadingincrease the liabilit to breakage of sucker rods; .A final modi cation of thel curve is brought about by increasing very slightly ythe actuating force and the added acceleration thus obtained permits the gradual change from a maximum to a minimum load such as shown by the curve B in Fig. 14. The data for these tWo curves shown in Figs. 14 to 17 inclusive, are taken from ah example in which the number of cycles 16-2/3 per minute, this time being taken for convenience of plotting the curves since onel degree `of band-Wheel rotition is then equivalent to 1/100 of a secon The curve indicated by B in Fig. 14 represents the motion Which is produced by the apparatus of my invention. The periods of acceleration and deceleration may be very accurately arranged to agree With what is considered the most desirable mo-tion of the pump plunger. Comparing the'cur've A. of

ig. 14, Which is for the ordinary crank and pitman, with the curve B, which is the -motion produced by my invention, it Will be seen that there quite a reduction in maximum stress and quite a reduction in range of stresses, and that there is no abrupt change in loading on the sucker rod. The maximum.

load in curve A is 10,21() pounds, Whereas the maximum load of the curve B of my inven-` tion is only 8,127 pounds. rlhe maximum range of' load for curve A is 7,520 pounds, Whereas for curve B of my invention it is only 5,144 pounds. The stroke of the maximum load of my invention covers substantially seven-tenths of the time period of the up stroke as illustrated by the curve Bof Fig. 14.""1`he1stroke of mini/mum load, also shown by curve B, covers substantially the same portion of the time period of the down stroke. The curve B of Fig. 14 may be replotted to co-ordinates of force and displacement'i'nstead of force and time and tle results Will be as shown by the curve of Fig. 15 which is nothing more or less than an ordinary engine indicator card with a late cut-off. lnrother vvords, if an engine were designed to operate Without a Ifly-Wheel andA With a variable stroke and Were to be attached directly to the beam, as shown in Fig. 1, it would automatically bring about a motion of the rodsI which would be similar to that of this analysis. In the curve of Fig. 15 the expansion is not like that of an engine since the object of the curve is simply to bring about a gradual change of load. rllhe manner in' which this change occurs is not material. An indicator card in the formof Fig. `15 taken from the engine in actual service would be useful in determiningthe pumping conditions and the friction in the Well. i'

1 claim as Vmy invention:

' 1. A method of operating a `plunger of an oil Well pump thro-ugh a string of sucker rods in. order to reduce the maximum stress set up 1n the sucker rods and to reduce the the stroke is six feet and` yset up in the sucker range of stresses set up in the fsucker ,rods, said method' comprising: accelerating said sucker rods during the greater part of the up stroke thereof, thus causing the maximum tensile stress setI up,in said sucker rods to be of relatively low value; decelerating said sucker rods during the lesser'part of said up stroke; accelerating said sucker rods during the greater part of the down stroke thereof thus causing the minimum stress set up in said sucker rods to be of relatively highvalue; and decelerating said plunger during the lesser part of said down stroke.

2. A method of operating a plunger of an oil Well pump through a string of sucker rods in order to reduce the maximum stress set up in the sucker rodsl and to vreduce the range of stresses set up in the sucker rods, said method comprising: accelerating said sucker rods substantially uniformly during substantially seven-tenths of the time of the up stroke thereof, thus causing the maximum tensile stress set up in said sucker rods to be of relatively low value; decelerating said sucker rods during the lesser part of said up stroke; accelerating said sucker rods subst antially` uniformly during substantially seven-tenths of the time of the down stroke thereof thus causing the minimum stress set up in said sucker rods/to be of relatively highvalue; and decelerating said plunger during the lesser part of said down stroke.

3. method of operating a plunger of an oil Well pump through a string of sucker rods in order to reduce the maximum stress set up in the sucker rods and to reduce the range of stresses set up in the sucker rods, said method comprising: accelerating said sucker rods during the greater part of the up stroke thereof, thus causing the maximum tensile stress set up in said suckerrods to be of relatively loW value; decelerating said sucker rods during the lesser part of said up stroke at a rate which Will reduce the stress until at the end of the up stroke, it substantially equals the minimum stress set up in said sucker rods; accelerating said sucker rods during the greater part of the dovvnstroke thereof thus causing the minimum stress set up in said sucker rods to be of relatively high value;and de'celerating said plunger during the lesser part of said down stroke at a rate which Will increase the llt) stress until, at the end of the dovvn'stroke,

oil vmll pump tlrough a string of' sucker rods'inorder to reduce the maximum stress rods and to reduce the range ofi stresses set up in the suckerrods,

4` A method of operating .alplunger of an y said method comprising: accelerating said sucker rods substantially uniformly during substantially seven-tenths of the time/ofthe up "stroke thereof, thus causingthe maximum tensile stress -set up in said sucker rods to be ofy relatively low value; decelerating said sucker rods during the lesser part of said up stroke `rat a rate which will reduce the stress until atthe end'of the up stroke, it substantially lequals the minimum stress set up in said sucker rods; accelerating said sucker rods substantially uniformly during substantially seven-tenths of the time of .the down stroke thereof thuscausing the minimum stress set up in said sucker rods to be of relatively high value; and decelerating said plunger during the lesser part of said down stroke at a rate which Will `increase .the stress until, at the end of the down stroke, it substantially equals the maximum stress set up in said sucker rods..

5. A method of operating a plunger of an oil well pump through a string of sucker rods in order'to reduce` the maximum stress set up' in the sucker rods and to reduce the be set up in the initial portion of the down.

stroke; accelerating said sucker rods during the greater part of the down stroke thereofv thus `'causing the minimum stress set up. in said sucker rods-to be of relatively higli value; and decelerating said plunger during the lesser part of said down stroke at a rate which Will increase the stress until, at the end o'f the down stroke, it substantially equals the stress desired to be set up in said sucker rods in the initial portion of the up stroke.

6. An' apparatus of the class described comprising: a plunger adapted to reciprocate in a barrel; a string of sucker rods connected to said plunger; a Walking beam connected to said string of sucker rods; a piston connected to said Walking beam, said piston adapted to reciprocate in a cylinder; a valve adapted to control the admission of and emission of a gas from said cylinder; means for positionin said valve to admit gas to said cylinder or forcingsaid pistondovvnvvard;`means for positioning said valveto shut olf said gas, said gas in said cylinder expanding to move said piston to the lower .end of its stroke so that comprising: aplunger adapted to recipiocate iii a barrel; a string of sucker rods connected to said plunger; a Walking beam connected to saidstring of sucker rods; a piston connected to said walking beam, said piston adapted to reciprocate in a cylinder; a valve adapted to control the admission of and emission of a gas from said cylinder; y

means for positioning said valve to admit gas to said cylinder for forcing said piston downward; means for positioning said valve to shut ofi" said gas, said gas in said cylin- 'dcr expanding to move said piston to the lower end of its down stroke; means for positioning said valve to emit gas from said cylinder to 'permit `said piston to rise in saidcylinder; and means for positioning said valve to prevent further emission of gas, said last named means adapted to opcrate before said piston reaches the upper said piston will be decelerated.

8. A method as set forth in claim 1 in which the up stroke is given more time than the down stroke.

9. An apparatus of the class described poinprising: a plunger adapted a reciprocate in a barrel; a string of sucker rods connected to said plunger; a piston operatively connected with said string of sucker rods; a 'cylinder in which said piston is adapted to slide, there being a closed expansion chamber formed in said cylinder by said piston so thatfluid .admitted thereto under pressure' tends toraise 'said sucker i rods; valve means controlling an inlet into y said chamber and anoutlet from said chamber; a highpressure tank connected to said inlet; a low pressure tank connected to said outlet; and a vcompressor adapted to draw Huid from said low pressure` tank and force it into said high pressure tank,.the circuit of fluid between said chamber, said 10W pressure tank, said compressor, and said hi h pressure tank being normally closed to t e atmosphere. l I

In testimony whereof, I have hereunto set y hand' at Los Angeles, California, this 22nd day ofV October, 1925.

WILL I-I. CLAPP.

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