US2078301A - Exhaust control for a pump operating motor - Google Patents

Description

April 27, 1937. w. H. WINEMAN 2,078,301

EXHAUST CONTROL FOR A PUMP QPERATiNG MOTOR Filed July 21, 1955 3 Sheets-Sheet 1 A ril 27, 1937. w H. WINEMAN 2,073,301

EXHAUST CONTROL FOR A PUMP OPERATING MOTOR v Filed July 21, 1955 I s Sheets-Sheet 2 April 27, 1937. v w. H. WINEMAN EXHAUST CONTROL FOR A PUMP OPERATING MOTOR 5 SheetsSheet 3 Filed July v21, 1935 Patented Apr. 27, 1937 PATENT OFFICE EXHAUST CONTROL FOR A PUMP OPERAT- ING MOTOR Wade H. Wineinan, Michigan City, Ind., assignor to Sullivan Machinery Company, a corporation of Massachusetts Application July 21, 1933, Serial No. 681,544

'26 Claims.

My invention relates to pumping apparatus, and more particularly to pumping apparatus for use in connection with oil wells.

v In some oil fields there is a considerable quantity of oil available, but not at suflicient pressure to cause the oil to rise to the surface; and under such conditions devices for pumping the oil must be resorted to. A-satisfactory system includes a number of pumping units arranged within a reasonable area and comprising power-operated mechanisms supplied with air from a central air compressor having pipes leading therefrom to the pumping units. In a preferred formof such apparatus, the unit at each well includes a pump head in the form of an expansible chamber, single-acting motor to which preheated air is supplied at a. substantial pressure; and a back pressure is maintained on the pumping motor sulficient to control the rate of downward movement of the pump-rod line, pump plunger and motor piston when the pump plunger is in engagement with the oil in the pump'barrel. Sometimes the pump plunger rises at a. speed a little greater than the speed at which the oil will flow into the pump barrel, and the plunger therefore leaves the upper surface of the oil, and during the early part of the opposite stroke a portion of the retarding effect is not present, and therefore the pump-rod line, pump plunger, etc. attain a speed greater than is desirable, and there is a substantial shock when the pump plunger engages the oil which partially fills the barrel. Such a condition is known as pounding down. This leaving of the oil by the piston can not be 35 wholly avoided, because if the pump were slowed down in order to avoid this-condition it mightnot be possible to keep the oil level low enough to cause the necessary rate of flow to the pump.

On the other hand, unless some provision is made 40 to preclude the rapid drop of the pump plunger and pump-rod line, the column of -fiuid in the pump barrel is likely to be struck so hard by the plunger that the. tubing may be split from the pressure and shock produced by the blow.

It is an object of this invention to provide a mechanism for preventing the evil consequences of pounding down while still allowing a pump to be operated at such a rate as to keep the oil level low enough so that oil will be produced in 50 the necessary quantity to warrant operating the pump. It is another object of this invention to provide an improved device for retarding a desired portion of the stroke of a pumping motor and thereafter removing the retarding effect.- It is still another object of this invention 'to provide'an improved pumping motor having improved valve mechanism associated therewith for controlling a portion of thestroke thereof. It is still another object of this invention to provide an improved valve mechanism connectable-to a pumpof stand- 5 ard form and operative, without interfering with the normal operation of the :pump motor valve mechanism, to modify the movement of the pump piston. Other objects and advantages of this invention will subsequently appear. 10

In the accompanying drawings, in which for purposes of illustration I have shown two forms which my invention may'assume in practice- Fig.1 is a side elevation of a pumping system in which an illustrative form of my improved 15 control mechanism is incorporated.

Fig. 2 is a. larger view, with parts in vertical section through the pump motor, showing one of the illustrative forms of my improved control mechanism. 20

Figs. 3 and 4 are detailed views, respectively partially and wholly in section, showing detail sections of the pumping motor per se.

Fig. 5 is a view similar to Fig. 1, showing part of a pumpingsystem in which the other illustrative embodiment of my invention is incorporated.

Fig. 61s a central vertical section through the control mechanism shown in Fig. 5.

Referring to the drawings, and first particularly to Figs. 1 to 4, inclusive, it will be noted that a platform or derrick floor 1 has mounted upon it a suitable frame 2 of structural-steel or the like. This frame has a top 3 from which there is pivotally supported-at 4 a pumping motor 5. This pumping motor is provided with an admission valve mechanism 6 and an exhaust valve mechanism '1. Air from a central compressor (not shown) is supplied, say-at 240 pounds per square inch, througha line 8 toa preheater 9, thence through a pipe l0, throttle valve ll and pipe [2, 40 to the admission valve chest 13. Fluid admitted past an admission valve 14 enters a pump motor cylinder I5 and raises a piston l6 which is attached through a piston rod l6 and a pump-rod line Ifi with a lift-type pump (not shown), which discharges on its up stroke and which is put in the bottom of a well. During down strokes of the piston IS, the exhaust fluid is discharged past an exhaust valve ll, through one illustrative form of a connection l8 and through my improved auxiliary control'mechanism, generally designated i 9, to an exhaust line 20, which is maintained under a substantial back pressure, for example 80 pounds, and which is connected to the intake side of the central compressor.

The admission valve 14 is controlled by mechanism including connected pistons 25 and 2t and a spring 21; and suitable fiuid supply connections 28 and 29 lead from the pistons 25 and 26, respectively, to a port 38 relatively near the bottom of the motor cylinder and to: any one of a selected number of ports 3i (depending upon the amount of expansion of the working fluid desired) relatively well towards the top of the cylinder. Of course the ports 3| not in use are suitably plugged. The cross sectional area of the valve It may be equal to the sum ofthe effective areas of the upper surfaces of 25 and 26; the area of 23 may be one-half the eifective area of 25, and spring 2'! may exert, when the valve 14 is closed, a pressure equal to one-half the per-square-inch inlet pressure. During the up strokes of the piston, the port 3% is opened first, supplying pressure through connection 28 to act downwardly on the piston 25. Thereafter;

port 3| is opened and pressure acts, through connection 29, on the top of the piston 25. Pressure upon both surfaces, added to that of the spring 21, closes the inlet valve i l, and thereafter the piston moves upwardly, throughout the remainder of its stroke under the pressure of the working fluid expanding within the cylinder.

The exhaust valve H is also controlled by a double piston and spring mechanism, including a piston 33, another piston 34, and springs 35* and 35 The upper end of the piston 36 may be equal to one-half the upper surface area of 33, and the sumof these areas may be substantially equal to the area of the valve ll. The spring 35 may exert a pressure equal to onehalf the per-square-inch line pressure, and spring 35 a pressure of perhaps five per cent of the per-square-inch line pressure. The piston 33 may be subjected to pressures within the cylinder through a connection 36, and the piston 34 similarly subjected to pressures within the cylinder through aconnection 31. The connection 36 communicates with the bore of the cylinder at a point 38 therein, substantially above the point of communication 1%. Connection 3'5 communicates with the bore of the cylinder at a point 39, substantially above the points of communication 3l. During the up stroke of the piston I6 pressure is admitted first to the piston 33; and later, when the piston reaches approximately the top of its upward travel and passes above the point of connection 39, pressure is admitted to act upon the piston 34; and then the pistons 33, 34 and the spring 35 cooperate to open the exhaust valve l! against cylinder pressure and the pressure of spring 35 and the piston it is free to move downward, under the weight of the pump-rod line, pump plunger, and its own weight, at a rate determined by the rate of flow past the exhaust valve I1.

On the downward stroke of the piston Hi, the pistons upper surface first uncovers the point of connection 39, and allows communication of piston 34 with the space above the piston l6, which is vented through a vent 48. The downward movement of piston l6 next vents the space above the piston 26 to atmosphere, when the port or connection 3! is uncovered by the upper end of the piston. Then, when the connection 35 is opened to atmosphere by the upper end of the piston l6, pressure is relieved from piston 33, and the exhaust valve [1 closes. Finally, when the connection 36 is opened to atmosphere the pressure is relieved from piston 25 and the admis-' sion Valve 14 opens, and the piston repeats its cycle which has been described.

If it is desired to operate the motor with expansion or compression, the mechanism shown in Figs. 3 and 4 may be applied. The mechanism shown in Fig. 3 includes a valve element 44 having operating mechanism 45, and it will be noted that this valve mechanism. includes a pair of seats 47 and 48. When the valve 44 is on the seat 41, the connection 38 determines the moment of closure of the exhaust valve H, but when the valve M is seated upon the seat 48, the motor operates Without substantial compression, and the exhaust valve is not closed until the port 30 is uncovered by the upper end of the piston. In a similar manner the mechanism shown in Fig. 4.- and generally designated 50 is operable to determine whether the motor operates expansively or not. This mechanism contains a valve 51 havingmanual operating means 52. There are twovalve seats 53 and 54. When the valve 5! is on its upper seat, uncovering of the connection Si by the lower end of the piston determines the time of closure of the admission valve. Whenthe valve 5! is on the seat 54, the admission valve will not close until the lower end of the piston uncovers the connection 39. For further details, if desired, of the structure and operation of this mechanism, reference may be had to my copending application Serial No. 612,538, filed May 20, 1932, which has now matured into Patent No. 2,004,146, granted June 11, 1935, and which more fully describes the pumping motor per se. t

With this understanding of the pumping motors operation, the structure and mode of operation of this form of my improved auxiliary controlling means may be described and readily understood.

Obviously, with the construction so far described,

as soon as the exhaust valve 51 is opened (which occurs when the lower end of the piston I6 passes above the connection 39) the pressure within the lower end of the cylinder would almost immediately drop to pounds per square inch, if that were the constant back pressure maintained in the line 29, unless some other control were superimposed. Now, if the pressure of 80 pounds is suited to the control of the rate of lowering of the motor and pump pistons and the pump-rod line, when the pump plunger movement is controlled, somewhat like a dash-pot, by the oil beneath it in the pump cylinder, if there be no oil for the first 6 inches or foot below the pump plunger, the back pressure is going to be inadequate to prevent too rapid a drop of the pistons and pump line, and a severe pounding will result. To prevent this, I have provided the mechanism [9. This mechanism includes a valve body 59 having a connection 6i with pipe element l8 and a connection 62 with discharge line 20. The interior of the casing 60 is divided by a ported septum 63 providing a valve seat 64. The spaces at opposite sides of the valve seat are connectable through a bypass 65 having a valve 66 therein for controlling the rate of flow through the bypass. A plunger 61- is reciprocable in a cylinder 68 formed in the upper part of the casing 60, and is adapted to move a valve member 69 down upon the seat 64. Fluid is supplied to the upper end of the plunger 61 through a connection H3 which is connected to open into the motor cylinder at a point I I, which may be changed to meet different needs by the provision of a plurality of openings '12 along the wall of the cylinder, with plugs 13 in the openings not used. The mode of operation of this form of the invention will be very easily understood.

As soon as the piston I6 passes above the mouth of the connection 'II, live motive fluid will flow from the cylinder I6 through the connection to act on the top of the plunger 67 and close the valve 69. Of course, the valve I1 is closed at this time, so closing of the valve 69 is entirely without eifect on the operation of the pumping motor at the moment when it occurs. Further upward movement of the piston I5 will supply pressure through the connection 31, which creates the condition necessary to open the exhaust valve I7, and the exhaust valve will thereupon open. This, however, will not permit in a normal manner the flow of fluid to the exhaust line 26, for the valve 69 is still closed. Some fluid will, however, flow through the bypass 65 under control of the valve 66, and this valve will be opened to permit the fluid to discharge from beneath the piston at such a rate as to minimize delay while still preventing pounding. As soon as the piston I6 passes below the mouth of the connection II, fluid will be exhausted from above the plunger 67 and the exhaust pressure acting on the lower end of the valve 69 will unseat this valve and the exhaust will take place freely through the remainder of the downward stroke of the pump piston l6.

It will be evident that the mechanism which has just been described will operate to provide a controlled initial downward movement of the pump and motor pistons and of the pump-rod line, thereby preventing the dropping of a great weight solidly upon the oil column in a cylinder partially full of oil. 011 the other hand, as soon as contact between the pumping plunger and the oil has been effected, or, if desired, slightly before this occurs (so. slightly that no undesirable momentum of the downwardly moving parts can be built up before contact) the parts of the pump system are allowed to move in their normal manner, with a minimum loss of time and Without marked reduction in the frequency of the pumping strokes.

Now turning to the other species of the invention, and referring to Figs. 5 and 6, it will be noted that all the parts are the same except that a new valve mechanism l9 has been substituted for the mechanism I9, and that the connection 16 leading to a point relatively well up in the pump cylinder has been replaced by connection 16 leading to a point relatively far down in the pump cylinder. The valve casing 19 is connected at with connection I8 and at 76 with the exhaust line 20. A ported septum 11 divides the interior of the casing I9 into two chambers 18 and 19, which are connected by an opening 86 in the septum. A cylinder-forming and closure member 81 is mounted upon the upper end of the casing I9 and closes an opening 82 therein. Member 8-I contains a-cylinder or chamber 83 in which a piston 89 is reciprocable. A valve member 85 having a spool or flange portion 85 relatively closely fitting the opening 86, is mounted within the easing I9 and has a stem 87 engaged by the piston 84 and also has a lower head flange 88 adapted to seat upon a shoulder 89 when the valve member 85 is in its bottom position, at which time the flange 86 substantially closes the passage 88. A spring housing 96 is arranged in alinement with the cylinder 83 but at the lower side of the casing I9. This houses a spring 9|, which has an adjusting element 92, and which presses upon the lower end or head 88 of the valve member 85.

A connection or port 93 is arranged to transmit the pressure in the chamber 18 into the space be-' low the head 88. The connection I8, previously referred to, connects the space above the piston 84 in the cylinder 83 with the interior of the motor cylinder I5 at such a point that, until substantially after free exhaust is desired, the lower end of the piston I6 will not close the motorcylinder-end of the passage I9. A bypass 95, having a suitable control valve 96, connects the spaces 78 and 19. i

The mode of operation of this form of my invention will best be understood by assuming certain pressures and areas. Let it be assumed that a pressure of 200 pounds exists below the piston I6 at the end of the up stroke (assuming the motor has operated with some expansion), and that a differential in area between the piston 84 and the valve-flange 86,- of A; square inch exists, the piston being the larger. The area of the shoulder 89 may be made very small and may be made, by suitable notching or the like, if desired, practically negligible in its effect. If the exhaust pressure in line 26is 80 pounds, it will be found that there will be a net pressure, holding the valve element 85 in the position shown, equal to 50 pounds minus .20 pounds or 30 pounds. The spring 9| will be arranged to exert an upward pressure of approximately pounds on the valve stem; therefore there will be a net pressure maintaining the valve in the position shown, equal to 5 pounds, at the moment the piston I6 starts. its down movement. The bypass 95 will permit the piston I6 to move downward, and begin to equalize the pressures between the chambers 18 and I9.

When the air flowing through the bypass reduces the pressure in chamber 18 and beneath the piston I6 to 180 pounds, the differential piston and valve areas will result in an unbalanoed downward pressure of minus 20, or 25 pounds. This the spring 9i olfsets, and accordingly any further drop in pressure will result in opening of the valve 86 under the action of the spring, and in free discharge of the exhaust to theline 29. The adjustment of the bypass controlling valv 96 will be made so as to delay the reduction in pressure necessary to open the valve 85 long enough to permit the pump plunger substantially to engage the column of oil in the pump haust flow occurs. On the up stroke of the motor, the exhaust valve I1 is of course closed, and as soon as the lower side of the piston overruns the mouth of the connection 70', pressure will be supplied on the top of the piston 84 and move the valve 85 to a closed position, and the valve will remain closed until again opened by a similar sequence of events to that described during the next down stroke.

In this construction it will be observed that I have also provided an improved device for retarding the initial portion of the down stroke of the pumping-motor piston in such a manner as to avoid pounding. Inthis construction, variation in the point of connection of a pressure line to the cylinder is not in any way made use of in order to provide for different travels of the piston to accommodate different degrees of separation between the pump plunger and the column of oil in the pump barrel; instead, merely by controlling the rate of discharge through the bypass, different distances of travel of the motor piston, prior to the beginning of normal relatively-free downward travel thereof, can be secured. In .both forms of my invention it will barrel before free expiston therein,

be obvious that the harmful eifects of operation during pounding down, as it is called, will be effectively avoided, and pumping in such a manner as to maintain the necessary low oil level can be advantageously and effectively accomplished.

While I have in this application specifically described two forms which my invention may assume in practice, it will be understood that these forms are shown for purposes of illustration and that the invention may be further modified and embodied in various other forms without departing from its spirit or the scope of the appended claims.

What I claim as new Letters Patent is:-'

1. In combination, a motor cylinder, a motor piston therein, admission and exhaust valve mechanism therefor having controlling means for effecting admission, cut-off, release, and reclosure of the exhaust mechanism, in definite relation to the travel of the motor piston, and means for retarding the discharge of fluid after release to delay the initial portion of the travel of the motor piston in one direction, said means having provision for varying the period of delay.

2. In combination, a motor cylinder, a motor admission and exhaust valve mechanism therefor having controlling means for effecting admission, cut-off, release, and reclosure of the exhaust mechanism, in definite relation to the travel of the motor piston, and means for retarding the discharge of fluid after release to delay the initial portion of the travel of the motor piston in one direction, said means having provision for varying the period of delay including an adjustably controllable bypass.

3. In combination, a motor cylinder, a motor piston therein, admission and exhaust valve mechanism therefor having controlling means for eifecting admission, cut-off, release, and reclosure of the exhaust mechanism in definite relation to the travel of the motor piston, and means for retarding the discharge of fluid after release to delay the initial portion of the travel of the motor piston in one direction, said means having provision for varying the period of delay including an operating piston having a supply connection variably connectable with the bore of the motor cylinder.

l. In combination, a motor cylinder, a motor piston therein, admission and exhaust valve mechanism therefor having controlling means for effecting admission, cut-off, release, and reclosure of the exhaust mechanism, in definite relation to the travel of the motor piston, and means for retarding the discharge of fluid after release to delay the initial portion of the travel of the motor piston in one direction, said means having an adjustably controllable bypass and also including an operating piston having a supply connection connectable with the bore of the motor cylinder.

5. In combination, a motor cylinder, a motor piston therein, admission and exhaust valve mechanism therefor having controlling means for effecting admission, cut-off, release, and reclosure of the exhaust mechanism, in definite relation to the travel of the motor piston, and means for retarding the discharge of fluid after release to delay the initial portion of the travel of the motor piston in one direction, including a valve casing connected between said motor and exhaust line, a valve movable in said casing and controlling discharge of the exhaust fluid, a pisand desire to secure by ton for closing said valve, a connection between said piston and the motor cylinder, controllable by the motor piston, and means for variably controlling the flow of fluid past said last-mentioned valve when the latter is closed.

6. In combination, a motor including a cylinder, a piston rcciprocable therein, admission and discharge mechanism having controlling means for effecting admission, cut-off, release, and interruption of exhaust in desired relation to the travel of the piston, and means for controlling the discharge of fluid released on opening of said exhaust valve including a valve casing, a valve controlling flow through said casing, means associated with said valve for providing an unbalanced area subjected to pressure in said motor cylinder during release and providing a pressure varying with the exhaust pressure in the cylinder tending to maintain said valve closed, means exerting a constant pressure tending to open said valve and means for permitting a controlled reduction of the pressure within said cylinder at the moment of release to effect opening of said valve.

7. In an apparatus of the character described, a motor cylinder, a motor piston therein, and fluid distribution means for said motor, and an auxiliary exhaust control apparatus including a valve casing having a septum dividing the interior thereof into two chambers, valve means cooperating with said septum to control flow through said casing, a piston for moving said valve toward said septum, and means for subjecting said piston initially to the pressure within said motor cylinder at the moment of release and subsequently during the same stroke of the motor piston to a reduced pressure.

8. In an apparatus of the character described, a motor cylinder, a motor piston therein, and fluid distribution means for said motor, and an auxiliary exhaust control apparatus including a valve casing having a septum dividing the interior thereof into two chambers, valve means cooperating with said septum to control flow through said casing, a piston for moving said valve toward said septum, and means for subjecting said piston initially to the pressure within said motor cylinder at the moment of release and subsequently during the same stroke of the motor piston to a reduced pressure including means for adjustably bypassing said last mentioned valve.

9. In an apparatus of the character described, a valve casing having a perforated wall dividing the interior thereof into two chambers, a valve member movable to cooperate with said wall in effecting control of flow through said casing, a piston alined with said valve, means for subjecting said piston to an initial pressure and thereafter diminishing the same, and means for subjecting said valve to the same pressures.

10. In combination, a motor cylinder, a motor piston therein, admission and exhaust valve mechanism therefor having controlling means for effecting admission, cut-oif, release, and reclosure of the exhaust mechanism, in definite relation to the travel of the motor piston, and means for retarding the discharge of fluid after release to delay the initial portion of the travel of the motor piston in one direction including a fluid retarding valve controlled by the pressure in said cylinder, said means having provision for varying the period of delay including adjustable means separate from said fluid retarding valve.

11. In combination, a motor cylinder, one end 7 of said cylinder 'connected to atmosphere, a motor piston in said cylindenadmission and exhaust valve mechanism for" the opposite end of said cylinder having controlling means for effecting admission, cut-off, release and reclosure of the exhaust mechanism indefinite relation to the travel of the motor piston, and means for retarding the discharge of fluid after release to delay the initial portion of the travel of the motor pise ton in one direction and automatically rendered ineffective during later'portions of the travel the motor piston in that direction.

, 12. In combination, a motor cylinder, a motor piston therein, admission and exhaust valve mechanism therefor having controlling means for effecting. admission, cut-off, release and reclosure of the exhaust'mechanism, in definite relation to the travel of the motor piston, and means for retarding the discharge of fluid after release to delay the initial portion of the travel of the motor piston in one direction, said means having an adjustably controllable bypass and also including an operating piston having a supply connection variably connectable with the bore of the motor cylinder.

13. In combination, a motor cylinder, a motor piston therein, admission and exhaust valve mechanism therefor having controlling means for effecting admission, cut-ofi, release and re closure of the exhaust valve mechanism in definite relation to the travel of the motor piston, and means for retarding exhaust only during the initial portions thereof having automatic pressure fluid governed control rendering the same ineffective automatically during the later portions of exhaust. a

14. In combination, a motor cylinder, a motor piston therein, distributing means therefor controlling admission, cut-off, release and compression in definite timed relation to motor piston movement, and exhaust throttling means automatically controlled to provide an initially restricted exhaust and a later removal of said restriction during continued exhaust.

15. In combination, a motor cylinder, a motor piston therein, distributing means therefor controlling admission, cut-off, release and compression in definite timed relation to motor piston movement, and pressure fluid governed exhaust throttling means automatically controlledto provide an initially restricted exhaust and a later removal of said restriction during continued exhaust.

16. In combination, a motor cylinder, a motor piston therein, distributing means therefor controlling admission, cut-off, release and compression in definite timed relation to motor piston movement, and cylinder pressure governed exhaust throttling means automatically controlled to provide an initially restricted exhaust and a later removal of said restriction during continued exhaust.

1'7. In combination, a motor cylinder, a motor piston therein, distributing means therefor controlling admission, cut-ofi, release and compression in definite timed relation to motor piston .movement, and motor piston governed exhaust V throttling means automatically controlled to provide an initially restricted exhaust and a later removal of said restriction during continued exhaust.

18. In combination, a motor cylinder, a motor piston therein, distributing means therefor controlling admission, cut-ofi, release and compression in definite timed relation to motor piston movementj and differential piston exhaust throttling means automatically controlled to provide an initially restricted exhaust and a later removal of said restriction during continued exhaust.

19. In combination, a motor cylinder, a motor piston therein, fluid distributing means providing admission, cut-off, compression and release in timed relation to the travel of said piston, and valve means structurally distinct from said dis-' tributing means automatically providing throttling of motor exhaust, during each occurrence of the latter, during only the initial portions thereof.

20. 1 In combination, a motor cylinder, a motor piston therein, fluid distributing means providing admission, cut-off, compression andrelease in timed relation to the travel of'sa'id' piston, and valve means structurally distinct from said distributing means automatically providing throttling of motor exhaust, during each occurrence of the latter, during only the initial portions thereof, said valve means having an area subjected during motor exhaust to the back pressure against which the piston moves and having a controlling piston having a connection opening through the motor cylinder wall between the limits of piston travel.

21. In combination, a motor cylinder, 2. motor piston therein, fluid distributing means providing admission, cut-off, compression and release in timed relation to the travel of said piston,

and valve means structurally distinct from said distributing means automatically providing throttling of motor exhaust, during each occurrence of the latter, during only the initial portions thereof, said valve means having an area subjected during motor exhaust to the back pressure against which the piston moves and having a controlling piston subjected throughout said throttling also to such back pressure.

22. In combination, a motor cylinder, a motor piston therein, fluid distributing means providing admission, cut-ofi, compression and release in timed relation to the travel of said piston, and valve means structurally distinct from said distributing means automatically providing throttling of motor exhaust, during each occurrence of the latter, during only the initial portions thereof, said valve means having an area subjected during motor exhaust to the back pressure against which the motor piston moves and having a controlling piston subject successively to the back pressure against which the piston moves and to atmospheric pressure during each nonworking pass of the piston.

23. In combination, a motor cylinder, a motor piston therein, fluid distributing means providing admission, cut-off, compression and release in timed relation to the travel of said piston, and valve means structurally distinct from said distributing means automatically providing throttling of motor exhaust, during each occurrence of the latter, during only the initial portions thereof, said valve means having an area subjected during motor exhaust to the back pressure against which the motor piston moves and having a controlling piston subjected to cylinder working pressure prior to release and to atmospheric pressure prior to compression.

24. In combination, a motor cylinder, one end of said cylinder connected to atmosphere, a motor piston in said cylinder, admission and exhaust mechanism for the opposite end of said cylinder for effecting admission, cut-off, release and reclosure of the exhaust in definite relation 10 cylinder for effecting admission, cut-ofi, release and reclosure of the exhaust in definite relation to the travel of the motor piston, and means governed alternately by pressures at opposite sides of the piston for momentarily retarding 15 the discharge of fluid after release to delay the initial portion of the travel of the motor piston in one direction.

26. In combination, a motor cylinder, one end of said cylinder connected toatmosphere, a motor piston in said cylinder, said motor having a pumping load throughout its working stroke and making its opposite stroke during the initial portion thereof only against a gaseous fluid back pressure and the remaining portions thereof against both a gaseous fluid back pressure and a liquid resistance, and means for admitting fluid to the motor cylinder to efiect the Working stroke, for interrupting admission thereto adjacent the endof said Working stroke, and for automatically providing a restricted exhaust during said first mentioned portion of said opposite stroke and a materially less restricted exhaust during the remainder of said stroke.

WADE H. WINEMAN;

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